Welcome back to the Commodore 64 repair project. If you haven’t read Part 1, it’ll provide the background to this project so I’d recommend having a look to begin with.
So, first things first, I only have one antenna cable between my Atari and Commodore, so I’ll need to cannibalize the RF antenna from my Atari. Annoyingly, one end of the cable connects to a port inside the chassis, so I’ll need to open it up first.
The inside of the Atari is rusty and dusty, and could probably use a bit of a clean and polish at some point, but It’s easy to remove the antenna cable.
OK, so this isn’t good. The last time I’d tried this I at least got something displayed. This time it’s only static. The only thing I can see is that a very weak signal is being received by the TV, as when I turn it on I see the above pattern. But, I have no way of knowing if it’s general interference produced by the C64, or just an actual signal.
So then I notice the antenna cable wasn’t fully in the switch box. Further inspection shows that that the two ends of the antennal cable aren’t equal. What if I swap them round so the longer prong is connected to the C64? Sadly, this doesn’t make much of a difference.
So, it could be the RF cable or switching box is at fault. There’s an easy way to test this; rewire it back into the Atari and see if it works.
And it does indeed work, and the Atari shows a clear signal. As tempting as it is to take a break and play a few rounds of Yars’ Revenge, it’s time to press on. And so the Atari gets put back together and goes back in the cupboard.
OK, time to open up the C64 and see what’s going on inside. This particular variant was colloquially known as the “bread bin”, and I’m guessing you can see why. The wire on the left hand side connects the keyboard to the motherboard. The one on the right connects to the power light, so I’ll need to disconnect both of these prior to going any further. The silver sheet covering the motherboard I assume is to shield it from any interference, but to me it just looks like a shiny bit of cardboard.
Pulling back the “shield” reveals the motherboard in all its glory. Of particular interest is the square silver box at the top. This houses the RF modulator unit.
After doing some reading, it seems there’s a way of tweaking the output frequency with a screwdriver, so it’s worth a shot to see if that has any effect. It’s the hole with the blue cross in it.
Taking the top off of the RF modulator reveals quite the labyrinth. I suspect it’s the small subsection in the top left which is responsible for generating the RF signal, or at least amplifying it enough for the TV. Tweaking the signal frequency doesn’t make much of a difference.
I hate to reach an anti-climax, but I don’t know how to fault-diagnose or fix an RF antenna. After watching a couple of YouTube videos in which someone attempts to repair one of these, I have to accept it’s well out of my ability, not to mention I lack all the equipment needed. Am I ready to go full-on hobbyist and invest in developing some electrical engineering skills? Not quite yet.
Is this the end of the line? Maybe not. If you ever owned a C64, you might know that it actually has two video outputs. The first is the antenna, but the other is a composite video out for which there’s a completely separate port. This was used by C64 owners of yore to connect their device to a dedicated monitor, rather than a TV. This would tend to result in a much better picture. In my case, it would have the added advantage of not needing the old TV to use it, as I could connect it to my existing monitor with the right adapter.
The good news is it’s possible to get an adapter to convert this port to HDMI. The slightly less good news is that I think the RF modulator does some of the signal processing needed for the other port to work, so there’s a risk this could be a dead-end as well. Still there’s no way to know without trying.
If I can get the video output working again, then I can proceed to reseating the various chips, which may fix the original issue with BASIC not booting. If all of these approaches fail and I can’t get it to work, there are still plenty of options available to continue this project:
- Purchase another broken C64 on-line for spare parts.
- Replace the RF modulator with a replacement board
- Substitute the motherboard with a modern replacement
- Replace the motherboard, chips and all with a complete solution
- Go down the Rasberry Pi route, replacing the motherboard with a Rasberry Pi hooked up to the existing keyboard as per this YouTube video.
- Turn the C64 into a glorified keyboard to use with an emulator as per this device.
- Give up an buy a Commodore 64 Mini (which will definitely look cute next to my NES and SNES minis).
So, lots of avenues to explore, just as there should be for all good hobbyist projects 😀
If you’re still on the edge of your seat, then come back and visit for Part 3 (hopefully) in a few months’ time!