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Dual Technologies SKD-4000

This beauty had been doing laps on eBay for a while. I had tried to low-ball it early on, only to receive a swift declination. A week or two later, I offered a little more and it was accepted! The seller took no time to send it to me, perfectly packed. It was listed as untested and with a cracked front-right case. Indeed it was, with one of the plastic clips actually hanging out the front of the opposing top-half, looking slightly like a buck-tooth.


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After a little googlin', I came across a site talking about a slightly different version to this laptop. Turns out Dual Group were a Taiwanese manufacturer and built laptops that were then re-branded and on-sold. They therefore didn't really have their own site with any relevant info on this laptop. If anyone manages to find any information on this laptop, then please get in touch in the comments section! I therefore kept inspecting the unit, disassembling what I could prior to needing a screwdriver.


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This unit didn't have a power supply, but thankfully the link above provided a pinout for the power supply their SKD-4000 needed. Under this unit, it stated it needed DC 20v @ 1.0A, so I tinned up a set of power wires and dialed in the voltage.

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Jamming the wires in the power socket, after continuity-testing for GND, I flicked the power switch... lo'an'behold: the full orchestra of a vintage HDD and a POST beep!

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The joy was very short-lived though... the BIOS quickly reported a low battery and incorrect date/time. Hardly surprising! I went into the BIOS anyway and did a HDD auto-detect.

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116mb, nice! I saved the config and rebooted, but nothing seemed to have stuck. Seems I'll need to replace the battery to get further. Before that though, does VGA out work?


Nice! Ok, back to the CMOS battery. The link above provided a tear-down guide to help me, but in the end I didn't really need it as this laptop was surprising easy to open and work with! Even the CPU had a flap for easy access? It also has DIP switches for setting the CPU and they seem to configure the CPU pins directly? I'll try and decode them shortly.


The CMOS battery is a piece of work. It's hard-soldered in and it happens to be a rechargeable coin-cell. These are pretty rare nowadays... and... stupid me... I just tried to solder in a coin-cell holder and use a CR2032. DO NOT TRY AND USE NON-RECHARGEABLE BATTERIES IN-PLACE OF RECHARGEABLE BATTERIES!

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Turning the unit on saw the coin-cell heat up rapidly, but fortunately I had my finger on the power switch, ready to prevent any spontaneous combustion. I then tried a 3.7v cell I had lying around, but the laptop started reporting 10 error beeps indicating that no battery was available at all. I really do hope I haven't trashed the charging circuit. At this point, I ordered an exact replacement Panasonic VL2330 battery and then looked for other things to fix up.

Power Plug

Whilst waiting for a battery to arrive, I realised I should solidify the power supply. Seems this type of plug is called a SnapNLock 4-Pin Mini DIN and I was pleased to see it available at Jaycar. I purchased a few (luckily) and attempted to wire one up. Soldering it was easy enough, but assembling it was next-level.


I mean, just look at the datasheet (which, actually, wasn't even east to find!), and you'll see what I mean... 8 components to jam together in a not-so-obvious order. I trashed the first plug and sorta-but-not-really succeeded with the second plug... it was good enough to test with.

Dip-Switch Dissection...

There are two blocks of four switches and, with no documentation, I set about trying to determine what these might control. Looking at the set closest to the CPU first, one can find the traces run off CPU pins.


Thanks to the glory of the internet, one can find pin maps and descriptions of pins readily available. The latter doesn't go into much detail, so actual CPU datasheets can also come in handy. After a little digging, it seems this block of switches controls maths error handling and interrupt line access to the CPU. I might just leave them as-is.

Dip-switch Name Solderable-jumper name Connected CPU Pin Pin Function
JP1-1 JP44 B15 NMI - Non-Maskable Interrupt
JP1-2 JP41 Can't tell... but seems to toggle the signal from JP1-1 through to JP3.
JP1-3 JP42 A15 IGNNE# - Ignore numeric error
JP1-4 JP43 C14 FERR# - Floating Point Error

The second block's traces disappear into the board's layers and are impossible to trace and understand.


Just for fun, I popped out the PLCC32 and read it in my Willem Programmer.


You can download the BIN file here.

Back to that Battery

A proper Panasonic VL2330 arrived and I soldered it in place. Applying power heard the same beeping. Ok, let's follow the traces to the left and see what's going on... two diodes, both seem to conduct power... then the voltage goes into pin 20 of that IC... with no marking? Why no marking?


Under the right light, it turned out to be an Epson RTC-6593 Real-time Clock. It even has integrated battery-backed RAM! Of course, this unit stores my BIOS settings. Why has the label disappeared? It's COOKED! It tried to burn me when I touched it. We can only assume it's due to my testing of other batteries... if only I'd bought the correct replacement at the start.

Replacing the RTC

So, I'm game to try this... what I'm not game for is fake chips! Searching for this IC has only come up with seemingly-dodgy sellers on Alibaba and eBay. I've just thrown in a few orders and we'll see what comes back. In the meantime I've removed the existing IC and cleaned up the area. Interesting to note that the silk-screen shows the IC should be an RTC-6583, whereas a 6593 was installed. The datasheet seems to indicate that 659x has "Extended Alarms" whereas 658x doesn't.


During removal of the chip, I just happened to remove a pad... I blame the fact that the IC was actually glued down to the board! I couldn't work out why the IC wouldn't move, regardless of the pressure I applied. Furtunately, it was a quick fix with winding wire and it's ready to solder up.

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I'll post a Part II once the ICs have arrived.

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