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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.


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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.

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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!

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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...

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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.

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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.

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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.


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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.

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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.

BW TV Animation

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.

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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.

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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.

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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.


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.


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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.

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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

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  1. Thank goodness i found this post! I was doing the exact same mod to an old Bentley portable TV i found at a thrift shop. I was lucky to have the same ICs as your TV!. Although, thank god i did not have to break the PCB to stop the signal, as there was a ‘resistor’ (note the quotes, it was a piece of metal wire as a placeholder) between the IC output and the input of the TV.
    Thank you very much!

    • Esteban, very glad to hear you managed to apply this trick to another TV.
      That metal wire may have been for an actual switch or socket on another model of the TV to allow proper composite input? Or maybe one of the engineers proposed to allow it in an earlier design and their boss chose against it as it wasn’t popular back when the TV was created?
      Either way, enjoy the crisp picture!

  2. Nice work! Would you be willing to help me figure out how to add composite video to a 1989 GE CRT? I made a post on reddit with all the info. Here is the link,

    • Dave,

      Sheesh, that’s a good one. I’d go with the ‘Video In’ pin between the U1401 and C2816. If you can scratch out the track and throw in a wire on the 1401 side, you can try feed in a composite signal directly. You can then provide a switch to bridge the trace or take a signal from an external RCA socket.

      For sound, it seems you need to follow the tracks into the ‘Sound Limiter Processor’. It’s hard to see from the diagram what tracks are actually available and I won’t have time tonight to check out the manual.


      • Thanks for for helping, Steve. I am trying to see if I understand this correctly. Are you saying to cut the trace directly in front of the “video in” pin on 1401 and then solder my composite lead directly to the video on pin? There is another thing I am confused about. The block diagram I uploaded on imgur is for a chassis CTC157 CRT and I see that it has two pins for “video in” (pins 3 and 9). However, on page 22 of my service manual for my chassis CTC149C set, pin 3 is labeled “in2” and pin 9 doesn’t have a label so does that mean that the pin layout for video switch is different on my CRT?

        I am asking out of curiosity, I am wondering why you are not recommending using pin 11 on the video switch to insert my composite lead as you connected your composite lead to the “video output” pin on your video IF processor IC? I notice that on the video switch, pin 6 is labeled “Aux video in”; is this pin designed to connect directly to an rca jack?

        Last question, instead of cutting a trace, is it possible to remove the first through hole component that is in line with the pin and then use the then available pad that is closest to the IC?

        • Dave,

          Can you please confirm what plugs are available on the back of the TV? I can’t seem to see RF input or a modulator in any of the schematics?


          • Hi, Steve, my set has two inputs and they are part of the tuner. The first input is RF and second is a twin lead connection (two screws) which older video game consoles used. My DVD player is connected to the RF jack.

            In my imgur album, I did post a picture of a schematic sticker that was inside of the back of my CRT chassis. It does show that my set has a tuner. There is a hot chassis tuner labeled TCHQ-1A and a cold chassis tuner labeled ADT1 as shown in the diagram. The back part of the tuner in the diagram also has a label CF1201 and in the schematic part list on the bottom of that sticker, for CF1201, it says QIF – SIF next to it.

            One other thing I did was upload another part of the block diagram from the chassis CTC157 set that shows the tuner.

            Here is the link to my imgur album again,

            • Evening,

              Seems I mistook the message above to mean the service manual was correct for your TV and not the initial diagram. Now that I realise the diagram is what we should be following and not the manual, I’m still leaning towards the Video In lines to the U1401.

              You could also just hijack into the pin 8 output of the Tuner Module if it’s outputting composite. Might need to skip the pre-amp and saw-filter modules, though.

              What I’d actually love to see is photos of the Tuner Module on the actual circuit board and a chip serial/model number to know what U1401 actually is. The code we’ve got is the GE number and not the actual chip model number?


              • The service manual is correct for my set and I did get it from Sam’s Photofact. My set has a CTC149C chassis and the service manual is for CTC149C. The block diagram I found somewhere on the internet before I obtained my service manual and it is for a CTC157 Chassis which was released one year later but the layout does appear to be identical compared to my schematic sticker.

                However, there is a new development. I took the back and looked at the locations of where U1401 and U1402 should be and they are not there. I just discovered by looking at the pics of the schematic sticker that is on the inside of my chassis, that some parts are omitted from some models (omitted parts have an “o” next to them on the schematic sticker list. I can see that U1401, U1402, U1402, U1700 and U1800 are not there just by looking at the board with the back off but I’d have to take the board out to see which other parts/ICs are not there. It looks like I got a very bare bones set.

                If it helps there is a “tuner terminal guide” on page 32 of my service manual if that helps. Let me know what you think.

                • Steven, I’m still interested in what you have to say about the composite mod but maybe an s-video mod would be simpler since the chroma and luma pins are right there on the jungle chip? Would I get sync right from the luma pin? How would the set know how to switch between RF and s-video?

                • Morning,

                  Apologies for dropping off… I’m guessing we’re in differing timezones!

                  The U numbers that you’re quoting are the codes for the schematic. I don’t believe they are the actual IC model numbers and that’s why I was hoping for an actual photo of the board in the TV so I can tell what the actual ICs are and then look up the datasheets.

                  Your idea of S-Video would be a good idea too. The idea is the same as injecting composite: you just need to lift a component directly inline with the trace and then switch in either the external source or switch back to the previous circuit. You don’t ever want them both feeding in at the same time.

                  • I am in the U.S. I’m still working on the photo. I can at least say that the model # of the jungle chip U1001 is in the service manual on a pic of the top of the main board. Strangely, it looks the U3100 and U 3300 are covered by a metal shield that is soldered to the board. I do know that the components I mentioned are missing because they are labeled on the top of the board with nothing there. I will still try to get the actual model #s of the chips that are there.

                    So, just to double check on how to do s-video, am I lifting the first component in line with the luma and chroma pin and then soldering in my wire leads on the free pad closest to the jungle chip? This would also include finding two ground points on the board for s-video. If this is correct, when I connect s-video, will the s-video signal show up on channel 3 or some other channel?

                    • Dave,

                      Thanks for pointing out that the circuit board picture is in the service manual. It seems to be an A23-1100-01A, but there’s no datasheet on the internet for it.

                      So… flying blind… you want to lift the component on the lines into 49 and 53. Possibly 56 instead of 53?, but I’d start with 53 first.

                      As for what channel on the display, the channel selection would be modifying the tuner, in turn modifying the signal into these pins. As that we’re disconnecting the feed from the tuner and injecting our own signal into these pins, the channel selection controls will have no impact on our input.

                      So, the basic idea would be to lift the U1001 side of the components for both inputs (sync and chroma). Once lifted, solder a wire into the hole that the component leg was previously in and a wire to the leg of the component.

                      From here we’ll need a DPDT switch. This switch would have 6 pins, split into groups of 3. For each group, one pin is common, with the other two being position A and B.

                      The two pairs of wires that you’ve soldered onto the circuit board will then be soldered to the switch. The wire from the component will go to common and the wire off the board will go to A.

                      We’ll then wire the signals from the S-Video cable into B on the switch.

                      Ground is a good one. I’d just ground them both on the GND pin of the U1001 chip. If you have a multimeter, just check for continuity to any of the component heatsinks. That might not be ‘signal ground’, but it’ll get you started.

  3. Thanks for clearing that up. If I don’t care about the tuner, would I be able to not use a switch and just wire s-video to the board and only use s-video?

    • If that’s the case, no need to use a switch… just disregard the de-soldered component (maybe insulate it with tape) and then feed the s-video into the two fresh holes in the pcb.

      • When you mention checking continuity to a component heatsink, would that mean using a multimeter and connecting one test lead to a ground pin and the other test lead to a component heatsink and then checking for continuity. What reading would I be looking for? My multimeter doesn’t have a continuity function but I could get one that does if I have to.

        • Also, does each of the 4 S-Video pins need to be terminated with a 75 ohm resistor?

          • I’m currently working on the s-video mod for my set and hoping to have it done tonight. For the sound, do you think it would be possible to tap into the volume control pin on the jungle chip? There is also a volume control pin (pin 37) of U3300.

            Another question. Do you think a used professional modulator from a company like Blunder Tongue would improve the picture over RF in case I ever wanted to use RF again in the future (I might for playing NES, watching VHS, etc.)?

            • The RF modulator I currently use is a Go Video DVD/VCR combo. The picture isn’t terrible but I do see a lot of picture noise and I’m wondering if a pro RF modulator would clean the noise up?

          • Howdy,

            For the resistance, I actually don’t know much about the levels required due to not having a datasheet for the chip. What you could do is measure them when the set is operating, but be very careful with the live electricity!

            Actually, the service manual has the voltages… I’d check to see if your voltages were in the same range and then add the resistors as required.

            As for the RF signals as you’ve mentioned below: I honestly don’t know enough about that world. I’ve happily made sure I don’t have to deal with RF again :)

            • Looking at the block diagram of U1001 in the service manual on page 24, it doesn’t look like the luma pin (pin 53) carries the sync signal but rather, sync is coming from pin 56 on U1001. Would I be able to solder a small wire to the pin 53 wire and then solder the other end of that small wire to a pad in front of pin 56 so that the luma and sync signals are combined in one wire.

              Also, once I measure the voltage at the s-video jack, is there a way I can figure out exactly which resistor I need without guessing? I believe that voltage at the s-video jack should measure .7V.

              • I wired everything up to an s-video jack but couldn’t get it to work. I did connect chroma to pin 49 and luma to pin 53 and the two ground pins on the s-video jack to two ground pins on the jungle chip (pins 39 and 50). I terminated the s-video ground pins, each with a 75 ohm resistor. All I was getting was white horizontal lines with black in between the lines. I did attempt to solder a wire to the luma wire and the other end to the sync pin (pin 56); same thing. Then I disconnected the first capacitor in line with the sync pin and moved the pin 56 wire there. I was still getting horizontal lines but some of the picture was coming through this time. I suspect this is a sync issue but I’m not sure what else to do. As an experiment, I did order a used professional RF modulator from a company called Blonder Tongue and this might give me composite video quality. I suspect there could be some cold solder joints in the tuner as the picture gets a lot of noise when I move the coax cable around. I might take out the tuner, open it up and check for any bad solder connections

              • Evening, sorry to hear we haven’t cracked this yet. Any chance you can send me a photo of the label of the RF modulator? It’s mounted vertically, so the service manual photo doesn’t show the serial/model number.
                My email address is stevenhoefel at hotmail dot com.

                • I uploaded pics of the tuner to my imgur album,

                  • Sheesh they couldn’t make it any harder. I’ve tried to search all of the codes listed on the modulator and nothing is coming up online.
                    Without the full data, it’s really hard to determine how to do this.
                    Apologies for the slow response and not being able to help!

                • Another question. I did order that Blonder Tongue RF modulator I mentioned. This meant I also had to order a male coax to female RCA adapter to use with the Blonder Tongue for my composite devices. I was thinking, if I just plugged one of these coax to rca adapters into my TVs tuner and just had the yellow video cable connected to it, would that be the same as composite video quality, since the tuner is only processing the video and not the audio. This adapter won’t come until Wednesday so I haven’t had a chance to try it out yet.

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