Retro « modelrail.otenko

27Sep/1612

Compaq Deskpro 386s/20n

I love old machinery. Apart from the physical presence and the sounds, there's no better reason to tinker with it other than to boot it up and play Railroad Tycoon Deluxe or A-Train. Therefore I purchased a dead Compaq 386 in order to revive it, install a sound card and listen to the beautiful adlib tunes of Railroad Tycoon's intro.

The machine

This poor thing hasn't seen much action for a while. There's dust caked everywhere and the outside of the case is grotty. It's actually a really nice design. Slim form factor with custom floppy drive. Well, not-that-custom... they've just taken the faceplate off and hidden it behind the front case panel. Obviously no room for a CD Drive, but I have a parallel-port model that should work perfectly.

Opening it up revealed just how custom and proprietary everything was. There was a non-standard power supply with a non-standard connector to the non-standard motherboard. Wait... it's not connected to the motherboard, it's connected to the vertical riser. That's not just for the ISA cards... it also routes power and data to both the HDD and floppy drive.

After a brief visual inspection, I performed the first test... apply power! I already knew it was dead, the seller told me so, so I didn't expect much. Hitting the power switch saw the fan twitch and the floppy drive light illuminate. It then repeated this at 1-second intervals. The power supply was trying to provide current but tripping straight away. No amount of unplugging peripherals would see it start.

Dead power supply

The first point about the power supply was that it wasn't a single removable unit. It's actually built into the case. There's a metal shield, holding the fan, that lifts off. The PCB is then bolted to the main chassis.

There were some telltale signs already: an odour of ozone and a large patch of fluid residue on the PCB and on the connector to the motherboard. That connector had me worried as well. It's the first time I've seen a direct connection, rather than a bunch of cabling and a plug, between the power supply and the motherboard. Once out, I looked more-closely at the power supply for any further defects.

Despite the residue, the capacitors actually looked in OK condition. There was no bulging or discolouration. Of course, looks can be deceiving! De-soldering them and looking at their butts showed a different story!

I thought to myself that this was now going to be an easy fix: just replace the damn things. Better point? I actually had replacement caps on hand. Unfortunately, after replacing all caps on the board with equivalent values I still had a dead power supply.

Replace more components, or buy a spare PSU?

Ok, here's the junction in the road... I mentioned above that the PSU was still dead... but in actual fact I had the HDD spin up for a brief moment! Something triggered the PSU to provide power, but this was short-lived. This could have been because it somehow saw 'load' on the pins, or because it momentarily chose to work. In my excitement, I put the motherboard back in and it all went dead again. Removing the motherboard didn't help; the HDD wouldn't spin up anymore. Still, the fact that the HDD was operational and the noise of that vintage drive spinning up was enough to keep me going.

From this, I could therefore point all fingers at the PSU. There was one on eBay, for over AUD$100, in the UK. That was an expensive gamble for, what could be, a very dead 386. Therefore, my first option should be to replace components in the PSU until it worked again. Looking at the board though, all 'areas of interest' were based around that nondescript Compaq integrated circuit. No amount of googling came up with any results!

The chip reads 114055-002/8072 (C) COMPAQ 1988 RAY H 9006. It's a 24-pin DIP and it's non-existent on the web. No real ability to replace this if I have no idea what it is! The other transformers seem to have dried fluid over them, but this actually seems to be from manufacture? There's a whole lot of power transistors of which look intact. Finding and replacing each one of them would total up to more than the other power supply on eBay is worth. Maybe I should just grab it? If I did then I could at least provide the pinout for this CPU for other users and maybe then repair this unit by working backwards from a functional one.

Further research revealed that the Compaq Deskpro 286N also uses the same PSU. The motherboard is just different, containing the 286 class CPU with all required components. Interesting to know that this 386 machine was built to use existing infrastructure from the previous CPU version. Either way, the googling amped up as I now had a wider scope of information to search for. Unfortunately there was still very little information on this PSU.

Decision to replace with an ATX supply

This was by freak chance. I went on lunch to find more capacitors for the PSU. I knew that these wouldn't help as they were only replacing caps that were actually obviously 100% OK. On the way to the electronics store, I passed a PC store that I've never really been in, as I thought it was all hoity-toity and full of brand new garbage. Turns out they had a random selection of secondhand gear out the back. I saw a tiny PSU (it would fit in the case!) that seemed to have one AT connector on it, labelled P10. Later googling told me that this was not an AT connector, but I got the PSU for AUD$20 when it had AUD$95 marked on it initially! Twas a sign... I purchased the header connectors as well as useless replacement caps.

There was work to be done to rewire the cable, but first we needed to know the pinout.

Determining the pinout

The power supply plugs into the vertical PCB. I don't know what you'd call this component? Maybe a distribution board? Junction board? Daughterboard? It's a vertical riser for the ISA slots, but it also has the plumbing from the disk controller. (Update: it's called a Backplane.) The best part is that the standard drive voltages flow through here. I therefore quickly determined the +12v, GND and +5v. These wires were often duplicated and comprised of the majority of the pins. In short time I had the first two columns of the table below.

Pin	Connection	ATX Colour	Comments
1	-12v	Blue	2nd pin, bottom row, MB socket 7th pin, bottom row, ISA socket I thought this was going to be a challenge... then I traced it to the ISA slot and found the connection.
2	-5v	White	5th pin, bottom row, ISA socket Thank you ISA slot.
3	+5v	Red	Traced to HDD power connector
4	+5v	Red	^^
5	+5v	Red	^^
6	+5v	Red	^^
7	GND	Black	These are grounded everywhere
8	GND	Black	^^
9	GND	Black	^^
10	GND	Black	^^
11	GND	Black	^^
12	+12v	Yellow	Traced to HDD power connector
13	Not Connected?		I attempted to pull up the plastic on the pin header to see if there were any traces connected. Can't see any!
14	Power Good?	Grey	5th pin, bottom row, MB socket Eep... buried in the motherboard... has to be Power Good?

From here, I had a problem... 2 of the wires fed into the dense motherboard socket. Tracing them further took a bit of work! Here I was assuming that the plug should be similar to a standard AT Power Supply Connector. Unfortunately not. It seems that Compaq (or Miniman) have decided to put a little more logic in the PSU than on the motherboard.

Further tracing saw wires heading to the ISA slots. This is perfect, as it's an industry standard and I could map them. I found -5v and -12v pretty quickly... the final pin went into the motherboard. Must be the Power Good signal.

Rewiring the ATX Power Supply

With the educated guess above on the 'Power Good' signal, I went ahead and wired up the ATX supply.

With the new cable on... I took baby steps towards testing. Firstly only the backplane with the HDD and floppy attached.

And then I plugged the motherboard and video card in.

Shittttt.... it woooorrrkkkeedd.... Before I switch to the software realm, I'll make this power supply more permanent.

Making the ATX supply fit

Fortunately this power supply was already tiny. Anything of normal size would not fit in the area provided and it didn't help that the original shielding was slanted. The fan was also mounted on the inside of the shield leaving little room for anything underneath.

I dismantled the new supply, destroying the leg on a component that was soldered directly onto the back of the power plug. I'd have to transfer these over to the old plug as I couldn't get it out of the case without a lot of extra work. Fortunately, the old power supply had the same component, so I stole one from there.

I soldered up the old plug as per the new plug's wiring. I then wired up the existing power switch. The old AT power switches had the entire 240v fed through them, and so are quite solid. I cut the plug off and used one pole to switch the green soft power from the ATX to ground. Worked perfectly!

I desoldered all the cables that I wouldn't need from the PSU. This was quite easy as they're fed in there in clusters! Mounting the fan wasn't fun... but it fit OK up the back on one of the screws that held the shield on. The shield then happily sat on top... a few millimetres higher than it usually would be.

Quick update: the fan mount was terrible. So I went and purchased a smaller 60mm fan and cable-tied it to the power supply PCB. It actually holds the PCB tighter and in place.

I previously stenciled out where I'd mount the fan, but now there's no need. Either way, check out the aftermath... here's the debris from the entire operation:

Motherboard Capacitors

Except for the self-test, I held myself back from booting the machine any further. I'd noticed that the rectangular capacitors on the motherboard were corroding and loose. Well, not all of them... 7 to start with, and after a plea for help on the electro-tech-online forums, it turns out I had the relevant 10uf 16v electrolytics in my arsenal.

Here's a good forum thread at Vogons where people are sharing similar experiences.

With these replaced, I attempted to boot the machine.

CMOS/BIOS issues

Of course, the hardware was never going to be the only problem. On the photo above, you can see the BIOS errors reported on first boot. The configuration data is held by a battery which as long-since expired. Back in the 386 days it wasn't a simple coin-cell either... but I'll talk about that later. Regardless of the battery state, I should have still been able to configure the machine.

Unfortunately, it seems that there is actual no BIOS configuration utility to 'enter' and so Compaq provided disks that loaded into diagnostic and configuration programs. Fortunately, other people on the net have also had to search for them and there were enough results on google. Download the self-extracting archive here. To use this, you'll need a double-density floppy disk. Turns out you'll also need an old machine! The EXE wont run on Windows 10. Virtual Box just threw errors with my real floppy drive and Windows 98 and so I built a brand new Windows 98SE install on VMWare Desktop. That burnt the floppy disk... but the disk then didn't work... it complained that it was the wrong version?

The screens above are as follows:

SETUP.EXE telling me I have the wrong machine.
TEST.COM telling me I have the wrong machine and to find a newer version of the software?
TEST.COM starting... nice logo!
TEST.COM initial diagnostics list
TEST.COM further machine detail

I tried a few other boot disks... All gathered from AllBootDisks. Starting the machine with DOS 5.0 and then running setup gave me: Packed file is corrupt. This is utter poop, as the same SETUP runs fine when booted by itself.

I then tried a DOS 3.3 bootdisk and it gave me the same errors as above: wrong machine, etc... So it turns out the DOS version determines how well the SETUP program runs. Maybe all these disks are crap because they were burnt via a virtual PC?

There's an entire list of the softpaqs available here. Searching gave me other possibilities, such as Compaq System Configuration Utility v2.58 Rev A SP19624 (actually, that's in Japanese), SP19619 (English), etc... But they're not matching my model. Actually, that index is for much more recent machines. I'd need something from this folder, but the index is incomplete.

But wait, thanks to the wayback machine, we have Compaq's support file listing from 1996. It's all close-but-no-cigar... there's a few interesting 'Rompaqs' in there. They seem to be the flashable ROM BIOS? Maybe there's a version specifically for the 386s/20n.

Hold the phone... the PDF here for the 386N shows my machine in the picture. The PDF here for the 386s/20n shows the 386/20. Were Compaq just lazy and pasted the wrong image? Further digging shows this awesome magazine advertisement from InfoWorld, 1991 (scroll up a little) where it shows my machine with the correct label... lucky... I didn't want a frankenstein.

Meanwhile.. the article here on the 386N indicates that the 'ROM Resident' setup utility (standard for machines of the day?) can be disabled via a dip switch. Well, I know of the switch, but I didn't know how to get into the BIOS. Someone here mentions F10 (find link), but then that is quickly dismissed as Compaq's needed diag disks. Maybe mine doesn't?

Well .. that couldn't be funnier. Indeed my machine just needs the correct keypress at the correct time.

See that shitty little block in the top-right corner? As soon as you see that, hit F10.

Man, we're in... time to configure disks. Wait. It isn't... we won't be saving anything until we fix the CMOS battery.

CMOS Battery

The motherboard has a DS1287 Dallas Chip for the clock/oscillator and battery backup. This unit is sealed. To get to the battery you literally have to hack it apart.

Fortunately, people have already done this. I've just bought the components to do this hack myself... so, let's spin up the power tools!

I half killed it. Be REALLY careful when grinding away at it. Either way, my configuration now saves! I even fluked it by getting a battery that has "Lithium Battery" on it in Katakana!

Disk Drives

So, we're booting and we can save CMOS configuration. The clock can't handle the year 2016, so let's pretend it's the year 1991. Due to this machine's vintage, the hard disk configuration in the BIOS is limited. Back then, there was a set table of known disk configurations. Each configuration specified the number of heads, cylinders and sectors which, when calculated together, provided the size of the disk. This machine was meant to come with a 120mb drive... this is option '50' in the BIOS, so I set that.

Reboot and I'm presented with 1782 - Disk Controller Failure. That's a really scary message... I would've preferred something worded with 'drive' rather than controller! What disk do we have in this machine anyway?

What on earth is a PlusImpulse? It looks like a Quantum... oh.. it is... tiny writing under the main brand name. Here's the specifications of the drive. No mention of the matching BIOS HDD table 'number'. Turns out that there isn't one. I found out the hard way by scrolling through the entire 60-odd options.

Quickly checked if the disk worked in my main PC via a USB-IDE adapter. Nothing! Dead drive! Turns out I have a 500GB (yes, gigabyte) IDE drive hanging around. So I tested that on the USB-IDE first and it worked. I then plugged it in to the Compaq and restarted. Same controller error! Quick inspection of the drive: it's in slave mode! Switched to master and there's no more controller error. YES!

That photo above still makes me chuckle. Who would've thought you'd ever see a 500GB drive in a 386? I slapped in a random Compaq FASTART DOS 3.1 boot disk and let it attempt to partition the drive. It really had no chance and kept failing miserably. I really didn't know what to expect when something this large was plugged in.

I tried another 200gb IDE drive which I had lying around. Configured as master, the BIOS then started throwing 1790 - Disk 0 Error. Putting the 500gb back presented the same error? Uh oh. Am I destroying the bus by putting these huge drives on that were never meant to be in 386s? I slapped the original 52mb drive back in and still had the error. Damn.

In the BIOS, to get rid of this error, I was about to set no HDD. Instead, for some reason, I chose a size that was just slightly smaller than the 52mb. On reboot, no error! I still had the DOS 6.22 boot disk in there and, as that I wasn't paying attention, it booted up. There was a different screen up... indicating that installing would overwrite the pre-existing system? What's going on here. I exited and checked out FDISK.

Hah. Wut? It has somehow found a partition. This disk didn't work on the IDE-USB cable... but now it's working here? Have I just, by complete chance, chosen the 'correct' BIOS setting that the previous owner used when setting up this drive? Actually, can you use any disk configuration as long as it is within the bounds of the disks parameters?

Either way, I let it reboot... but it still came up with non-system disk? It definitely tried to access the HD though! I rebooted into the MS-DOS floppy and then ran a benign SYS C:. I could see that all the other files were there, so it may have just needed the minor DOS boot files. Upon reboot... we got to a bloody C:\ prompt!

AUTOEXEC.BAT pointed to BASEPAGE which no longer existed, hence the errors. There's also a PRINCE folder... no idea. The obvious thing to test was Windows, which booted fine... Paint Brush worked a treat! IT'S ALIVE!... That's enough for tonight... I have more plans for it (hints in the next picture), but this article has gone on long enough!

This has been a blast.

12 Comments

15Sep/162

Amiga 1200: PCMCIA Wireless Networking

Who would've thought you'd be able to get a machine this old onto a WPA2 network? Not I. Either way, it's totally doable and makes getting files onto the system a LOT easier!

Requirements

You'll need a 16-bit Wireless PCMCIA card that's supported. You'll usually find one around the Amibay forums or on eBay. 16-Bit PCMCIA cards are recognisable via their difference in connector to newer PCMCIA cards.

As you can see, the little line of plastic that guides the card into the slot is thinner on the 16-bit card. This guiding line is on the right in the picture above. It's twice as high on the 32-bit card. Make sure that your cards are 16-bit and never try to force them into the slot!

Instructions

There's a great video How to set up a PCMCIA wifi card on a standard Amiga 1200 over at Daily Motion. Watch that, or follow the steps here.

First thing to install is the wireless driver. My cards are based on the Prism Chipset and therefore the Prism2v2 driver over on aminet is the best choice. The 'v2' version supports WPA (as long as your card does!) and is very easy to install. Click through the steps and configure your card. Make sure you have a 2.4ghz network available as, chances are, your card wont be doing 5ghz any time soon!

Once configured, the wirelessmanager will have been added to your user-startup. Restart your Amiga and watch the blinkenlights on your card to see if it associates. I'd recommend checking your router also, to see if your card is listed as a connected device. It won't have an IP yet, but the MAC address should be recognisable.

From here, you might need to install CardPatch and/or CardReset. These are useful if you have trouble restarting your Amiga with an active PCMCIA card installed.

TCP/IP

I've recently learnt that the Amiga OS 3.9 CD comes with TCP stacks included... but I haven't tested them. Instead I went ahead and used MiamiDX. Make sure you have MUI installed first and then go ahead and install MiamiDX and it's MUI support library. Throw it in the System or Utilities folder on your main drive.

Reboot your Amiga and then open up the folder where you installed it. Run MiamiInit. We're going to install a SANA-II driver and manually enter prism.device. Note that this is prism2.device and not prism2v2.device. Although we're using the v2 driver, the filename is actually just prism2.device.

Once added, tick through and make sure that DHCP is configured. Save the configuration as default.

Now go back to the folder where MiamiDX was installed and run MiamiDX itself. From the menus, choose to import a MiamiInit profile. This should then populate MiamiDX with all of your hardware configuration. Go to the Ethernet tab, highlight your device and hit 'Online'... within a few seconds your device should be ready to go! Finally, choose Save as Default from the same menu... then you wont have to go importing every time you open up MiamiDX.

Browsing the Web

You pretty much only have a choice between only two browsers. AWeb and IBrowse. I tried AWeb and was impressed. But it doesn't do SSL. Note that the installer mentiosn that you'll need ClassAct2 installed. DO NOT INSTALL CLASSACT2 on Amiga OS 3.9! It'll trash your 'classes' files and prevent even simple dialogs from appearing. Someone else learned the hard way here and had to re-install OS 3.9. AWeb will run fine on OS 3.9 as-is.

Here's an animation of AWeb trying to load Aminet. It actually loads the site 3 times before finally settling and loading images.

IBrowse has addons for SSL and Flash! The basic version installed perfectly well and loaded aminet a lot quicker than AWeb.

I'll try the add-ons shortly!

2 Comments

14Sep/160

Amiga 1200: System Sounds are Mono!

Working on vintage hardware, with a vintage set of speakers (yes, yes... wrong brand.. I know...) can cause no end of stress. Recently I set up the Amiga 1200 on my desk and used my trusty old AppleDesign Powered Speakers. I'd had issues with these in the past: One channel was soft and the balance was even at 75% left. After opening them up, I re-soldered a few dry joints and all worked well again!

I was nothing short of horrified when I heard the first beep from the Amiga. It only came through one channel. I checked the cables, the balance and jiggled everything... but to no avail. Further system sounds also failed to be broadcast over stereo.

Well... it turns out that system sounds are mono! Don't ever expect the base Amiga OS 3.9 to send sounds over both channels... as much as you mash the keyboard to make the actual beep occur!

Hippo Player came to my salvation and happily played Action on a street in full 2-channel glory!

It also turns out that I'm not the only person who has noticed this.

No Comments

13Sep/161

Amiga 1200: Installing OS 3.9 from USB

Not having had an Amiga when younger, I'm completely foreign to the basics. Due to this, I've managed to make a dog's breakfast of the main hard disk on my Amiga 1200. I had installed software from left, right and center and have started to have random issues. It got to the point where AmiDock couldn't find a correctly versioned library and AWeb just wouldn't load.

Due to all of the above, and my new understanding of the directory structure and basic OS layout, my weekend task was to completely rebuild the Amiga 1200's CF HD from scratch. I didn't want to cheat either... so I attempted to do it without using WinUAE to build the base image.

TL;DR: For those of you who just want to get something done... scroll down to the Amiga 911 Maker section. The first two sections are just me ranting and learning and breaking things. In the end, if I'd just used the Maker and built the disk I would've had the system up an running in an hour!

Bootdisk required - Amiga911

I needed USB to be available when my Amiga booted, the CD-ROM drive that I had was an external IDE boxed unit and I'd previously installed Poseidon with my Rapid Road USB card. After a little searching, I came across the Amiga911 Emergency Boot Disks. Unfortunately, the chicken-vs-egg scenario occurs straight away as I needed a bootable Amiga to be able to write a bootable floppy image! Fortunately, I did still have a bootable Amiga and managed to get to a shell to burn ADF images.

Glancing over the Amiga911 site, I chose the first basic disk image which included the Poseidon USB stack. Writing it to a spare DD floppy using adf2disk was easy enough. Unfortunately, upon boot I was presented with Software Failure; ramlib - Program failed (error #80000004). Wait for disk activity to finish.

I've dealt with this before: the reason for this error is that I have Kickstart 3.X ROMs from Cloanto and these need a specific library to be installed on the boot partition library folder. Instead of obtaining the library, I switched to a spare set of Kickstart 3.1 ROMs and managed to get further. Before I continue the saga, a quick note on ROMs: stock 3.1 ROMs are 1 pin shorter than the Cloanto versions. These need to be aligned to the RIGHT of the socket. ROM 2 is at the top, ROM 1 underneath. It is a fatal mistake to left-align them! i.e. make sure there is a spare pin on the left-hand side of the socket, as per below.

Where was I?... Oh yeah, I could now boot into the Amiga911 Emergency Disk! Progress was halted as I was quickly warned that I needed a real Workbench disk to proceed. I didn't have one in the flesh, so I had to revert back to my main partition to create one. Of course, the main partition would no longer boot as it seemed to expect the 3.X Kickstart ROM. I swapped them back in ... bending pins and putting them in the wrong order. Finally... after 3 failed boots (black screens) I was back at my crappy workbench. I wrote the Workbench disk to a spare DD floppy.

At this point I decided to actually copy the 3.X ROM libraries required to the Amiga911 Emergency Boot Disk so it would boot... that way I wouldn't have to swap the ROMs again. The library in question was workbench.library as mentioned on Cloanto's Site. Whilst trying to copy this over to the Amiga911 disk, I initially thought I was in trouble... the only file showing on the burnt floppy was an Activate Amiga911 executable. My brain then thought magic happened on boot and that everything was in compressed archives that got decompressed during startup. This actually is the case, but there are still base system files that need to be executed first. Of course, I wasn't showing all files and initially couldn't see them. After this I managed to find the Libs folder and copied the relevant workbench.library to it.

It then booted! A few presses of enter got me to a prompt asking for the workbench disk. I swapped to the disk I'd burnt earlier (note that this is the wbench image, not the install image) and ... upon 'press any key' it told me it wasn't a proper workbench disk. On second try, it worked. Seems I hadn't waited long enough the the disk poller to unmount the boot disk and mount the workbench disk.

Amiga911 then copied a whole bunch of files off the workbench disk and asked me to put the Amiga911 disk back in... making sure it was write enabled. I did as asked, this time with an obligatory 5 second pause between removal/insertion/keypress. The installation process then stripped hunks... I giggled. It seemed to be building a compressed system image on the floppy. The compression process then failed with a crappy write error (you could hear it coming by the repetitive noises the floppy drive was making)... I wonder if this was because I put a library on the disk that took up too much space? Funny thing was that the Amiga911 script considered the process a success... I don't think it correctly read the return code from the LZX utliity!

Either way, I let it finish and the rebooted the machine... it seemed to get quite a way but then bombed out with just a Workbench Screen title bar and no disk activity. So. Back to the start. I went through the process again with a newer DD floppy (yes, I managed to acquire a fresh box of floppies!) and it all worked. The disk was written. I then copied the workbench.library from my OS 3.9 partition to the floppy and restarted.

I was presented with an invalid library message and a hung screen.... no workbench! Yey. I attempted to use AmiKick to get the workbench.library from my 3.1 KickStart ROM, but this didn't help either. So... back to kickstart 3.1. The boot disk is built from Workbench 3.1, so using the 3.9 library was (in hindsight) an obvious mistake. It turns out that you can get the relevant 3.1 disks from Cloanto if you have a valid serial number and you register... I've since done this and might try this method again later just for shits and giggles!

Back to the main task, I chose to downgrade back to 3.1 to be able to continue. After another dangerous ROM swap, I had the Amiga911 disk booting. Turns out the base Amiga911 disk doesn't contain the drivers for my USB card though! I searched my OS3.9 disk and copied the rapidroadrcusb driver to the floppy. I also then removed the drivers that I didn't need. At this point, I was really starting to wonder if all of this effort was going to pay off! Upon reboot, I manually started the USB Stack (check the Tools menu in Workbench) and my USB Key appeared on the desktop. Ok... nearly there... I would also have to install AmiCDFS at this point.

And so I did that... I dropped the files from AmiCDFS (there's no installer) into the relevant locations on the floppy disk... watching it fill up... I think I had around 40kb free in the end. After another reboot, and a manual USB stack start, I had a frozen workbench. Oh joy.

This has to be the equivalent of DLL-hell in windows. I am sure all of these 40-something versions on libraries mean something... I mean... they could be decades apart and completely incompatible. At this point I'd realised I made a stupid executive decision when installing AmiCDFS: there was already a CD0 on the Amiga911 disk in Devs/DOSDrivers and I left it there... for some reason I thought it would be ok. I checked the files again and realised that the CD0 icon on the floppy was the old driver from the floppy, not the driver from the AmiCDFS archive. I re-copied this into Devs/DOSDrivers from the AmiCDFS archive and rebooted. After a reboot, I heard the CD spin up... but no icon on the workbench. I unplugged and re-plugged the CD Drive and ... SUCCESS!

So, at that point I had a USB stack running from this disk... from there I needed to actually install Amiga OS 3.9. Before doing so, I used SFSFormat and wiped the main OS partition that had supported me up to this point... no turning back now!

I had booted off the floppy, so the OS disk wasn't needed and the format went fine. Trying to then run the OS 3.9 Installer off the CD presented me with "Could not load required libraries." What the hell? All this way just to realise that the boot disk doesn't have the right files to allow the OS 3.9 Installer to function? I suppose that's why there is another disk available called the OS 3.9 Emergency Disk II? I seem to have gotten this far, on my own, but for no apparent point as there's another ready-to-roll disk that'll work better.

(Hindsight: That "Could not load required libraries." error was actually because of the Kickstart 3.X ROM!)

Using the Emergency Boot Disk II

Back to square one, I wrote the ADF for this disk to a new floppy. After a reboot it told me that the disk needed to be activated and that this had to be done from a standard boot and not whilst booting this emergency disk. So, back to the Amiga911 with USB floppy that I'd built above.

I swapped the new disk back in and then ran the activation program. It brought up the familiar console screen and told me to make sure that I had an Amiga OS 3.9 CD mounted. This was the case, so I whacked enter. I was then presented with errors...

Turns out that the keyfile for LZX is not on the Amiga911 boot disk. Fortunately, LZX has been freeware for a long time and you can get the licence file from here. Once back in Workbench, I copied it to the Ramdisk:System/System/L directory. Trying again... the disk built! Of course... it had the wrong USB drivers. I did the same steps as above and put the correct drivers in and AmiCDFS. On a reboot, the machine actually booted! Now, this was built off an OS3.9 boot image, so I swapped my Kickstart 3.X ROMs back in. Why not? OS3.9 is correctly supported!

After a reboot, I actually successfully installed Amiga OS 3.9 on my main CF card. It rebooted and all was OK! I then tried to install Boing Bag 1 and got all sorts of errors. Initially it was due to "failed execution 3" and then "Could not load workbench details". Both of these errors indicated a broken "installer". I replaced it with Installer-43_3 and then InstallerNG, but nothing worked... I couldn't complete the installation of Boing Bag 1.

After a little more searching, I realised that I'd put in all this effort for nothing. Amiga 911 actually comes with an Amiga911 Maker which will allow you to configure your boot disk parameters and then write a totally targeted boot disk for your machine!

Amiga 911 Maker

This application is very easy to use and provides a step-by-step GUI for building your boot disk. I had troubles using it with the Kickstart 3.X ROMs, but that could have been due to a broken base OS install. I do admit though, with the same install but with Kickstart 3.1 ROMs, the application worked flawlessly. I'm still trying to work out why that occurs!

Anyway, step through the application and configure your disk. The questions are all self-explanatory and the processes are numbered. You will need the Amiga OS 3.9 CD mounted to build a boot disk. At the end, slap in a blank or erasable DD floppy and write your disk.

After configuring, I rebooted my machine with the new disk and everything loaded flawlessly! A little painful after the effort spent above, but hey, we're getting somewhere. OS 3.9 installed perfectly and then all Boing Bag's (nearly) worked a treat! I haven't tried to switch back to the 3.X ROMs yet.

A quick note on Boing Bag 3&4

After finally getting 1 and 2 installed, I ran into an error with the combined 3&4 package. If I selected the A1200 as the model, I was presented with an error indicating that No help text specified in line 835. I extracted and re-extracted using both LHA and UNARC, but to no avail... the error kept appearing.

I dug into the files and realised that the Install file was nothing more than a script. The language was actually quite clean and tidy, based on indentation and parenthesis. I scrolled down to 835 and saw an askchoice which was meant to present a prompt on whether or not I wanted to update scsi.device. The askchoice above had an extra line in the definition providing the 'help' text whereas this one didn't. I therefore tried to add it via the ed command. Scrolling down to the line took a while, adding the line was easy, so was saving... but then I got weirder errors from the installer. It seems that ED truncates lines that are too long and does damage to the file! Instead I cheated and edited the file on Notepad++ on windows.

Fixing this line allowed me to install the Boing Bag!

Further software to install

I want to try ClassicWB. There's a specific distro for the A1200 running OS3.9. I assume this installs updated icons... if not, then maybe NewIcons or something similar.

1 Comment

1Sep/160

Amiga 1200: Rapid Road USB

After cross-grading from the ACA1220 to the ACA1221, I'd decided that USB would be an easier transfer mechanism over PCMCIA to CF cards. USB would also allow more peripheral options, as opposed to PCMCIA ethernet cards and CDROM drives.

Whilst purchasing the ACA1221, I also purchased the Rapid Road USB interface. This kit comes with all you need to add two USB ports to an Amiga 1200. It's all been sitting in a box for quite a while as I've been distracted by other tasks.

Hardware Installation

The Rapid Road slots on nicely to the ACA1221. As that the ACA1221 is a smaller size, there is ample room and, once on, the whole kit takes up the previous size of standard accelerators. I did find that the unit didn't seem to plug all the way on. It definitely makes contact though. It might be advisable to somehow provide a backing support beam to keep the Rapid Road in place.

You need to connect power from the Rapid Road to the ACA1221 and then the ground wire to the chassis. The floppy drive screw provides a good location for this. There is no need for any other cabling, apart from the USB plugs themselves!

Some might call it butchering... I call it creative-license. Yes, I didn't really measure or calculate a precise entry for my grinder, but in the end, the USB sockets are firmly installed. I used M4 screws that I had lying around and drilled them into the rubber of the plugs.

Everything fit back together nicely. The trapdoor cover is now an essential part of this Amiga 1200!

Software Installation

The USB stack used is known as Poseidon. You can find the links on the Icomp.de Rapid Road Wiki Page. Once downloaded, get the LHA to the Amiga. Of course, you can't do this via USB yet!

Installation was very next-next-finish. The default options put everything in the correct locations. Once the installer finishes, the USB stack is actually loaded! I had already put my USB key into the slot and the bloody thing showed up on the desktop. It also made a really funky space-ship sounding noise... turns out this happens upon device insertion.

At this point, I thought I was done. I rebooted the Amiga after playing with files on the USB key. Upon reboot, I got an error from the startup script: PsdStackDLoader not found. Turns out that this script is created once you've gone through the configuration. This is done via the Trident Prefs file which you'll find on the drive you installed Poseidon to.

Run through this, it's all pretty self-explanatory. As long as you chose the correct driver during install then it'll be selectable. It should come 'online' after configuration. Make sure you save all your changes at the end. I didn't configure any further classes or devices.

On the next reboot... my USB Mass Storage Device was mounted again.

USB CD-ROM Drive

I have an external drive and tried it... unfortunately it needs more power than the USB ports put out. I'll be finding a powered hub shortly and will test this again.

The hub in the middle didn't help... it just chewed more power as I didn't have an adapter for it! Turns out that buying a powered hub didn't help either... I needed a specific cable that provided two-ports-worth of amperes to power the CD unit.

Ok, we're now recognised... I can see the CD drive in the Trident prefs tool... but we don't have a CD mounted on the desktop? What gives?

Ahhh... big hint there. I needed to download and install AmiCDFS. After doing so, and rebooting, I had a CD mounted on the desktop! I got lazy whilst installing AmiCDFS and just dragged the C, L and LIBS folder to OS:. I expected this would merge the folders, and it did, but it also overwrote the icons! Must be stored in folder metadata somewhere.

A quick check of what was on the CD...

...and then a great time was had by all destroying the landscape!

No Comments

17Aug/160

Atari 2600 jr: Controller Maintenance

I'd purchased two controllers from Holland (Game Over? in Amsterdam) and had received two more when I picked up this Atari from the rubbish dump. I have finally gotten a game worth playing and thought I'd test them all out.

The game is Bezerk.. and it literally is just that. Think of a 'top-down' Space Invaders. You're a human, you're in a maze and there's robots who want to shoot you. If they (or you) touch a wall then you're dead. Your goal is to knock them all off and enter the next room. It's really quite challenging for such a simple concept.

This game is only playable if your controller works! It turns out that only one of mine had problems. This specific controller would not happily move left/right. Up/down and the buttons worked... but I couldn't get my guy out of the way reliably on the X axis. A little more testing realised a cable fault! If I put pressure on the cable, right where it enters the controller, then I could move in all directions... the cable must be internally fractured.

Pulling it open, you can see the cable come in from the top. It then slaloms through the plastic pins to keep any unwanted pressure/tension off the solder joints on the PCBs. Too much flexing, over time, has ruined the cable. The only method was to cut it and shorten the cable.

The cutting, pairing and soldering was quite painless. I unsoldered an existing wire and then soldered on the new wire, matching colour-for-colour. The end result was a perfectly working controller! It turns out you can even shoot diagonally in Bezerk!

Two of the four controllers I've acquired used to have the screw-in joyticks. One of the other two actually still had the joystick in place! For the ones that have been snapped off, I grabbed a screwdriver and applied enough pressure to have the phillips-head torque the plastic left-over out of the thread.

Now to find a suitable replacement screw-in joystick!

No Comments

11Aug/169

Toshiba T2000SX

It's a hard fact that one can fail when restoring old hardware. This ancient laptop was purchased from an auction house and has lived in my old university school bag, in the back of the parents shed, for a few decades. It booted, back in the day, and I vaguely remember installing Windows 3.x on it. After that... you couldn't really do much other than play Railroad Tycoon Deluxe.

Seriously heavy, this thing is built to withstand nuclear fallouts; although it turns out it couldn't handle being in the shed. Turning it on again after so many years presented a hard drive exhibiting that charming click-of-death tune. The screen worked fine, the keyboard accepted commands and the floppy even seemed to function. After counting its on-board RAM, extended RAM and then extra ram (if you had the PCMCIA-like card installed (which this came with.)), the BIOS would ask you to insert a floppy disk.

As that the hard disk was dead, I'd decided to replace it with a compact-flash card. Other people online had successfully done this and so I thought I'd give it a go. The installed Toshiba BIOS wont recognise anything other than a Conner 'IDE' 20/40mb drive that usually comes with such a laptop and so I had to improvise. One user online pointed out that Anydrive would fix this. It's a tiny application which slaps an assembler JMP in the MBR to lie to the BIOS when it goes looking for the specifics. From here you can mimic the drive/partition information that the BIOS wants to see... you can't override the 'device ID' though.

Installing the CF card was easy enough... The CF-IDE adapter just plugs everything together and has the appropriate pin missing to guide the correct connection. At this point I actually used VirtualBox (with a hack to allow direct disk access) to install Anydrive onto the disk. I used the parameters from the Conner: Quick Reference Guide For Disk Drive Products (Cylinders 980, Heads 5, Sectors 17) with anydrive, inside VirtualBox, and it installed. This way I didn't need the floppy disk. I then tried to format the drive, but nothing worked... it kept failing. I therefore went ahead and installed it into the laptop so I could use the floppy drive there.

The machine booted up and the Anydrive message actually appeared! The bios actually read from the harddisk and then failed... the harddisk wasn't partitioned, so I had to use a DOS bootable floppy to continue. I downloaded an appropriate DOS 5 boodisk from allbootdisks and threw it in. Nothing... it just repeatedly asked for the disk. You could hear it sort-of read the disk... but it didn't get anywhere.

First step... try the disk cleaner... didn't work. Second step... rip it open. Not an easy task. The main chassis is a single block of metal. The top circuit board must be lifted. To do so, you need to disconnect all the flimsy ribbon wires.

Wait... what's that... oh great... the remnants of the drive belt. And it's not a happy elastic-band. It's a very proprietary, very flat, very thin ribbon belt. Screw it... let's try a rubber band anyway!

Did it work? No... it took out the read head. Game over. Drive finished! A quick google proved no quick answers to finding a replacement drive.

Do I care about a crappy 386 laptop at this point? No. I put the majority of the system back together to check if I could still use the HDD. No go there either... the HDD (well, CF card) was no longer being found and the Anydrive boot message was not displaying! No more disk input... stuff it. Here's the aftermath... it then all got shoved as-is back into the school bag.

It's currently sitting next to the bin and I'm finding it hard to take the final step and listen to it bounce down the garbage chute. I've failed you, you poor old thing.

9 Comments

10Aug/162

Atari 2600 jr: Composite Video Output + Audio

There seem to be a lot of options (and sites with comparisons of the options) available when adding composite video to the Atari 2600. Some require removing parts and disabling the RF output whereas others just hitch onto components and allow both signals to be produced. Here's a brief list of places to find information:

There's also hardware that you can purchase to make the job a lot easier:

Doing it yourself

I chose the mod available at Lynx's 0,68 Euro ATARI 2600 Junior Composite Mod (German). This mod offered a good balance of circuit complexity and as little atari-destruction as possible. All parts were purchased from the local Jaycar, except for the 330ohm resistor. They were out of stock and so I combined a 300ohm+33ohm.

Here's the final parts list:

1 x 330 Ohm 0.25w Resistor
2 x 1K0 0.25w Resistors
1 x 2K2 0.25w Resistor
1 x 3K3 0.25w Resistor
1 x 100p Ceramic Capacitor
2 x RCA sockets

Construction was very straight-forward... I soldered straight onto the pins and scratched a pad for ground on the nearest plane. I then quickly wired up an RCA plug. I knew I'd need to de-solder it again to mount it into the case, so I didn't over-do the soldering.

Great picture! This is the start screen for the 4-in-1 cartridge. All good... now for audio.

Above you can see two wires heading to the required spot at the base of the resistor. One is folded up... I intend on doing the stereo mod next, so that's there for future-proofing. Currently mono audio is output via the white RCA socket.

UPDATE: My 'future-proofing' was useless... the PAL version of the Atari 2600 jr DOES NOT support stereo sound. So just connect the red plug to the white plug internally!

Now... to play games...

2 Comments

9Aug/160

Atari 2600 jr: Introduction

This was an unexpected surprise. Canberra has a rubbish tip; well, a few, actually. At these tips, back in the day, the dumpers used to drive their cars/trailers/trucks right up to the wall'o'rubbish and offload. Whilst the father was scraping all the rubbish out and launching the bags onto the mountain of junk, the children would be scavenging through other people's discards.

I found many a thing there: old computers (286/386, at that time), model railway paraphernalia, misc. electronics, etc... After a while, too many dead bodies were being found and so they closed the dumping area off to the public. Instead, they built a concrete shed with a big mechanical compactor. Everyone's rubbish was thrown in a corridor and compacted. A truck would then drive it up to the real landfill area.

The public could no longer freely recycle other people's rubbish. It was lost once it went over the wall. An uprising occurred when an entrepreneur decided that he could form an organisation that worked at the tip under appropriate licensing (oh, I love democracy) and legally scavenge the rubbish. This was no good, unless they could actually sell it... so a 'shop' was set up at the rubbish dump. Can you believe this? We have to buy our rubbish back?

Either way... last Sunday... after 2 separate (and dismal) trash and treasure markets, I ended up at the Green Shed. I was initially looking for a bootable DOS disk... not finding much, I was disheartened and about to leave. As you exit the building, you pass the cash register, which is actually a large glass display cabinet. In it was a lost treasure. The attendant had me made: he knew I wanted it and happily quoted a price which would've doubled the takings for the day of the entire shop... but, for the unit, was half the going rate on eBay... as long as it worked!

My first Atari

Last year, I read the book: Racing the Beam. I can't remember how I came across it, but it ended up being a good read on the inner workings of the Atari. I was impressed to find out how they got around hardware limitations and changed the way kids would play games forever.

I had never expected to own one. Especially one in this condition... It turns out this is the Atari 2600 Junior. It's the final version, slimmed down, produced somewhere between 1986 and 1991. It was brown when I got it...being in Canberra, I didn't have any tools with me, so I used floor-cleaning wipes (disinfectant was a great idea at this point) and tore the thing apart. After a good clean, it actually came up remarkably well. The best part was that the 'protective seal' was still on the steel Atari branding on the top of the case. I should've left it on there... but I really love peeling those things off!

The whole loot included two game cartridges, two controllers (one had the screw-in joystick snapped), the base console and the wall-wart. The only thing that was missing was the RF cable. I cleaned it all at home in Canberra. Taking it apart, the solder joints looked fine... there was just a large accumulation of dust. A quick vacuum and wipe down got it into the state above.

I bit the bullet and plugged it into the wall. Toggling the power switch did nothing! Bummer... a dead Atari... I was very happy to have a new project. I popped it back open and scanned all components again. There wasn't anything obvious. I thought I'd leave it until I returned to Melbourne where I could go over it thoroughly with the multimeter. After re-assembling, I quickly tested it once more. The fourth toggle of the power switch saw the red power LED light! Ok... we're in for fun if the grime has gotten ALL THE WAY into the 'enclosed' power switch.

A more complete teardown

I returned to my workbench at home and pulled the machine apart; knowing that there were going to be gremlins in the system. Overall, it looked to be in great condition, but I grabbed the magnifying glass and inspected it all again anyway.

The metal shielding comes off very easily. The top half is secured to the bottom half via metal tabs that have been slightly twisted. Grab a pair of pliers and bend them all straight again... you'll then find that both shields come apart with little force.

After an inspection, I re-vacuumed the switches and grabbed a cartridge. I really wanted to check out Ghost Busters, so that was the obvious choice. Using my trusty BW CRT TV, I hoooked it all together. Scanning the UHF channel, I found no signal. I could get interference when I toggled the power switch, so I thought that I was near the right tuning every so often. I was on UHF because that's what the Commodore 64 used and I assumed that all consoles of that vintage would use the same frequencies. I was wrong. The Atari 2600 uses VHF Channel 2 or 3. This channel is selectable via the switch at the back of the console.

Once on VHF tuning, the signal appeared easily. The console was set to Black and White, so the image was crisp! Even over RF. I wonder if these can do composite? Ghost Busters is pretty hilarious. Actually quite difficult to get started... but I think I'll write a post just for that story.

Top Push Buttons

The Select/Reset buttons to the right of the cartridge port, on top of the console, are spring-loaded via a 'sponge'. This material had deteriorated on both buttons over the decades and needed replacing.

I happened to have some packaging material foam on hand and sliced some pieces off to replace the worn out sponge. I scraped the old sponge off first... needed a bit of elbow-grease for this ... was definitely stuck on well! Afterwards I used a bit of double-sided tape to apply the new sponge.

Worked perfectly.

What's next?

Why, games! I've got a total of 36 to test out... so I'll flick through them and report on anything noteworthy. I also want this thing producing a composite signal... so a little research will see that occurring in no time.

No Comments

4Aug/1626

Commodore 64: Using an ancient BW TV

Using the Commodore 64 on the main TV produces a really great picture over the composite cables, but using it via a converter to VGA or via RF is a little dicey. I like the idea of 1:1 picture when using composite, there's no need to covert the signal. I also don't always get to use the main TV, so I went hunting for a suitable display for the Commodore 64.

Turns out that last weekend I was in luck. Whilst rummaging at the local Trash and Treasure I stumbled across a Samsung LCD TV (RF, VGA, Composite and Component in!) and then... the holy grail... a tiny, portable, black-and-white CRT Television! Check out that hideous battery pack.

It happily allows you to scan the VHF/UHF airwaves; unfortunately there aren't any signals broadcast in this spectrum anymore. Actually, at the low end of VHF I got a local radio station, but no picture. It has the option for an external antenna, but this used a mono 3.5" audio jack.

Hooking it up to the C64

The external antenna jack was easy to work with. Opening the TV (runs on DC voltage, but BE VERY CAREFUL WITH CAPACITORS NEAR THE TUBE), I inspected the circuitry and found that the in-built telescopic antenna was also wired into the jack. This makes sense: plugging in the external antenna disables the internal antenna. The jack functions as a nice routing switch, choosing between sources when the jack has a cable plugged in.

With this knowledge, I chopped up a 3.5" audio cable that I had spare and worked out which wire was ground. As expected, it turns out that the shielding was ground and the very tip (the white audio wire, red is unconnected) made contact with the RF input pin and disabled the internal antenna. With this, I then cut an RCA lead and joined the relevant cables. The C64 has a single RCA-style port for the RF output. Plugging the wire together, I then started scanning the airwaves.

I vaguely remember, from back in the day when tuning in a brand new Nintendo Entertainment System, that most consoles output a frequency somewhere near UHF channel 60. I happened to start at the 'top' of the UHF band, but after winding the dial to the other end I had a picture!

There was further tuning on the side. Contrast, brightness and V-Hold allowed me to get quite a clear display in black and white, of course.

The fun part now was taking a quality picture of the tube. Shutter speeds are usually way too quick to see the full image... the camera can easily beat the scanline. I therefore slowed the camera down. Using this theory, I also had fun and sped the camera up...

Hah... nice... very easy to see how the tube works. That Horizontal scanline illuminates a bunch of dots/pixels and does it fast enough to resemble a whole picture to the slow human brain.

Testing a game

My first cartridge was acquired from Game Over? in Amsterdam. This is 'Rat Radar Race', a game I'd never heard of. It was purchased because I didn't want to leave the shop empty-handed and, for quite a while, I've wanted to test out how cartridges work.

I plugged it in and turned on the machine. I was amazed to find that it booted straight into the game. Very seamless and very fast! With floppy disks and tapes you actually had to enter BASIC commands to boot. This method is much nicer!

The best part? Audio! The RF cable was dodgy, but functioning quite well. The picture and hideous audio was being output rather well. I tried the game for a bit: You're a mouse, there's three of you... you navigate a maze by holding down the arrow of the direction you wish to turn next. Scaling the maze, you pick up cheese. If you hit a cat or a fellow 'blind' mouse then you fail. The theme music is actually the 'three blind mice' 'melody'.

RF Modulation/Demodulation

Just like an old dial-up modem, the RF mechanism for getting your console to display on your TV is inefficient. RF was meant for radio waves; the goal was to be able to transmit images over long distances. The tuner in the TV is therefore capable of tuning in to differing frequencies, producing different channels on your display.

This is overkill if your console is sitting right next to the TV. There is no real need to convert to a lossy format, only to make the TV find the signal and convert it back to a displayable format. Hence, TVs later added extra inputs for 'direct' signals. After RF came composite, SCART, Component, VGA, DVI, HDMI, etc... The Commodore 64 can actually produce a composite signal (as I was using on my other TV), so I wonder how hard it would be to provide a direct composite input into this little TV?

Bypassing the RF input and providing Composite

Turns out that this is totally achievable. The job of the 'tuner' circuit in the TV is actually to produce a composite video signal to rest of the video circuitry. The main question is: Where do I inject the composite signal from the C64 without destroying the TV, the C64 or endangering myself?

Our first step is to inspect the circuitry and determine what ICs are used. Next we'll check out the datasheets and then try and work out a method for signal injection. The signals we are talking about are available 'naked' on the back/front of most audio/visual components, so shorting them out is possible in the real-world and therefore shouldn't damage our equipment if we happen to do so. The main issue is when you wire up the signal to a power rail or other high-voltage feed... such a process wont end well!

I would first recommend that you review a few BW TV Schematics to understand what basic components are used. Ralph K has a great article: TV and VCR tuner modules which has a schematic for a tuner that shows how the fundamental components are connected. The tuner IC actually seems to be a mirror of the one used in this TV... either way, it still helped with the circuit tracing.

A quick scan of the circuit board in this TV shows that it was built on a suite of Samsung chips. There's a KA2133 - 1-Chip Deflection System that provides the synchronisation for the tube. There's high voltages down in this area, so be very careful around the large capacitors!

Up under the tube is a KA2101 - Linear Integrated Circuit (TV Sound IF Amplifier). Not exactly what we're after, but we'll need this after we get the video fed in.

Top left of the board is the RF 'tuner'. Actually, the left-most box is a de-modulator. It does the opposite of what the RF modulator inside the C64 does. Unfortunately, it's not as simple as the modulator; it needs to be fed in variable parameters to determine the exact frequency to demodulate at. The C64 merely has a fixed set of parameters to modulate the signal.

You can see the wires running from the front panel into the space between the demodulator and, what I believe is, the tuner next to it on the right. This tuner is also shielded, but from the underside of the board I can see it has an IC in there. With a good torch and a little more disassembly of the chassis I was able to read the model of the IC. It is a KA2912 - Video IF Processor for BW TVs. Bingo. That datasheet also shows that Pin 3 is the video output.

The underside of the circuit board also has the pin numbers for the IC. How awesome for us? And for the assembly line lemmings who constructed it. Thanks to PIN DETAILS OF IC A-Z, BASIC ELECTRONICS AND ANTENNA : KA2912, we can see that it actually outputs a composite signal!

Injecting an external composite signal

From here, we're going to do damage to the circuit board. The first step is to bare the trace running to pin 3 by scratching the protective coating away. I've used my pocketknife to do this.

Next we need to actually cut the track. Use the sharpest tool you have and scratch the track at a perpendicular angle, slicing a gap into the board. Make it a little wider than 1mm. A flat-head screwdriver can be used once the initial cut is in place. Now that you've got pads to solder to, tin the areas that are bare. Make sure that you don't have any solder bridging the gap! At this point I then turned on the TV to test it. No picture? Perfect! The signal from the UHF/VHF tuner has been severed.

At this point, as a test, we're going to hook the composite RCA plug directly into this track. It's better to find out as early as possible if we've got the track or location wrong. If there is no picture when you do this, then you'll need to dig further into the datasheets and determine a better location to cut in the signal.

I hooked up the trusty C64 and ... it worked! Well.. nearly... the picture was scrolling and buzzing awfully. Turns out that there are two GROUNDs in on the circuit board. There's the 'signal ground' and 'supply ground'. If you, as I did with a paper-clip, ground the incoming signal to the supply ground then you'll get a shit signal. I then tried grounding to the other signal ground and got a much clearer picture. It was still rolling though.

What could be the problem? I quickly rotated the V-HOLD trimpot and had no luck... picture still rolling. At this point, I should have stopped ... breathed ... rolled the trimpot slowly... and tested it properly. But I didn't... instead I went and re-adjusted EVERY pot on the board. In fact, I didn't keep an initial record of what they were all set to and COMPLETELY de-configured the TV. I then spent another night re-configuring based on guesses from the photos I took for this blog. Painful... There were also fragile wires around the tuner circuit of which I managed to break free of the circuit board; these then required resoldering and reinforcing. Finally, I was nearly back to a functional TV again, the final issue being that a trimpot I replaced was grounding against the tuner RF shield! After fixing all these mistakes, I had a rather reliable picture.

Now that this was certain, I went about inserting a switch that selected between the antenna plug or the composite input. This was a DPST switch, as I wanted to switch the mono audio as well.

Now that I had a quick way to switch between both inputs, I plugged in both the RF signal and the Composite from the C64.

For the standard BASIC screen, shown above, the picture was very nice on composite (first picture) and quite blurry on RF (second picture). Either way, they both showed well.

Above is the display difference of a game cartridge. It actually seems that the cartridge is changing how the C64 outputs the picture! The first picture is composite and seems to be over-scanning? The second is RF and is happily rendered within the bounds of the picture tube. I wonder if that's PAL vs. NTSC or some other timing issue. Or maybe because I happened to alter all the trimpots and de-configured the TV. I'll keep digging.

Audio

The same trick was then applied to the sound channel output by the KA2101 - Audio amplifier. Documentation, other than the datasheet, on the KA2101 wasn't so easy to find, so I searched for similar devices. Turns out the MC1358 is a clone (let's not get into which one was created first) and there are quite a few circuits available online as examples of audio amplifiers.

If you look here at TradeOFIC, you'll see a stereo amplifier. We don't need 2 channels, but we do need to know where to inject our composite audio signal. On the mid-left of the diagram, you'll notice that they have an input select that cuts the line from Pin 8 of the MC1358 and splices in audio from an external plug. I love it when it's this simple! There is a capacitor on the other side, so we'll check our circuit and cut in after that if we have one too.

The circuit was cut and the wires were hacked on. I then fed via the external audio input via the same DPST switch that I used for the audio. I only need to switch one wire as ground is common (remember to use SIGNAL ground!) and the audio is mono, so there is only one audio and one video wire. Having a TPST switch would've allowed for 'future expandability', but I cannot see myself installing stereo speakers into this little beast.

The best part? It seems that feeding a proper audio signal in with the composite video stabilised the video signal! Look at that crisp picture!

Looking back...

This was not an easy task... this post was written around 4 nights after I started pulling apart the TV. Take your time with old electronics. The case was brittle and the circuit board had been repaired and re-soldered.

One thing I didn't mention above: I had to replace one shotty capacitor and I destroyed a trimpot. Don't forget that flexing wires around will break their solder joints... so expect to re-tin the majority of contacts under the board. Go nuts and replace/re-tin ANYTHING that looks suspicious!

Capacitors are a standard item to replace. Cell batteries are usually next in line for leaking. You're bound to find all sorts of issues with vintage items. Good luck!

Other References

26 Comments

« Newer Entries Older Entries »

Random Photos

DSC07902

Otsu - May 2019
Photo Album Index

modelrail.otenko Trains, computers, vintage, retro, model railways… the lot…

The machine

Dead power supply

Replace more components, or buy a spare PSU?

Decision to replace with an ATX supply

Determining the pinout

Rewiring the ATX Power Supply

Making the ATX supply fit

Motherboard Capacitors

CMOS/BIOS issues

CMOS Battery

Disk Drives

Requirements

Instructions

TCP/IP

Browsing the Web

Bootdisk required - Amiga911

Using the Emergency Boot Disk II

Amiga 911 Maker

A quick note on Boing Bag 3&4

Further software to install

Hardware Installation

Software Installation

USB CD-ROM Drive

Doing it yourself

My first Atari

A more complete teardown

Top Push Buttons

What's next?

Hooking it up to the C64

Testing a game

RF Modulation/Demodulation

Bypassing the RF input and providing Composite

Injecting an external composite signal

Audio

Looking back...

Other References

Random Photos

Search

Tags

Ads

Archive

Meta