So I've got this C64 that I came across some years ago that exhibits a number of odd problems. I set it aside as a pet project (no pun intended) to work on should I come across a spare C64 to gut for chips.

That time has now come. This past weekend I was able to purchase (rather cheaply) a C64 with a dodgy power supply but otherwise working. As luck would have it, like my sick C64 with odd errors, this C64 has socketed chips and is the same board revision and everything (both 1984 models, and this board: http://upload.wikimedia.org/wi...d_1984.jpg). So I'm ready to go to work. Since I'm not handy at all with a soldering iron (indeed I don't even own one), but I can manage slotting in and pulling out chips, I figure it best to take the good chips out of the C64 with the dodgy power supply, and use them to repair the strangely-behaving C64.

However, before I go screwing around here replacing chips all random-like, I thought it prudent to hop on here and give a decent description of the problem so as to narrow down the (possibly) offending chips without needing to replace each and every one of them on the board, but also not screwing up both machines so that neither is in a non-operable state.

The first major symptom with the sick C64 is its sound. Only one of the sound channels plays correctly. The other will make noise, but has no volume control, and indeed the notes will stick "on" on that channel. The third channel does not sound at all.

The second problem, most apparent after playing around a bit, is the colors of the characters on screen do not behave properly. On bootup, the screen appears normal (light blue border, dark blue interior with the usual C64 BASIC message across the top, and the READY message). However, when trying to programmatically change colors using a simple POKE command, sometimes that works and sometimes it does not. Also related to the graphics issue, some sprites will not appear. So, for example, if I play a game like Donkey Kong, instead of the correct colors showing, I get an almost entirely red primate at the top. Also, the barrel colors don't appear correct either.

Now, with my bare minimum knowledge about the chips and how they interact and all, I'm guessing this might be caused by a busted SID and VIC-II. But I wanted to confirm all that on here first before I go playing around with my machine to get more insight on the matter.

I don't follow. If the new c64 you picked up works, why not use it?

Years ago mine was doing the same thing, if you pushed the power connector in too far or too hard it wouldn't power up. And when powered up the slightest knock would crash the computer. Took it to the shop and they just soldered up the power port in place.

Buying a soldering iron and locking that into place seems simpler than ripping out and replacing chips.
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Well, as I said, I don't have soldering equipment of my own, nor do I trust my skill to such a project (I'm a programmer, not a hardware specialist, so my command of hardware is limited to installing cards and chips that can be socketed easily).

However, I do have access to a friend that is handy with electronics, so I called him. He came over with his soldering equipment and a voltmeter, and we set out to work on the machines to get one of them working.

What we immediately found out was that the power supply socket itself apparently has a short up in the plastic housing, which was apparently the problem. So when I told him about my original plan, he decided it might be easier to try that first and see what happens (he has big hands and it was a bit difficult for him to get in there to work on the power socket itself).

To aid us, I pulled up some schematics for those chips, and he set to testing them with his voltmeter that he brought along. We found that, sure enough, it seems to have been the VIC-II and the SID that had gone sour on the flaky C64 with good power. The rest of the chips tested good. So we swapped just those two with the known working ones.

Everything fired up and worked just fine. Perfect sound. Perfect graphics. And a 100% working (for the moment) breadboard C64 for me. And one totally busted one, of course.

I have the same issue with one of my machines as well, some of the tones seems to "stick" until I press the firebutton or do an action that triggers another sound. My other machine has a space-button that does not work. Unfortunately, I have no idea what to do.

Is there a site out there with f.a.q about c64-problems and how to fix them?

There are these two sites that I used as a reference to somewhat pin down the problem.

If you have an original model C64: http://personalpages.tds.net/~...c64-ic.txt

If you have the C64C model: http://personalpages.tds.net/~...4cdiag.txt

Of course, my problem wasn't specifically defined in the text file, but that's because I had two different chips that went bad, both the VIC-II and the SID. That's what led me to conclude the problem was the sum of both chips, and not just one or the other.

Sounds to me like in your case, if it's only a sound problem, it might be your SID. As for the spacebar problem, that could be a control chip, or it could just be a faulty keyboard. The keyboard is easy to swap with another for testing. That'll help you weed out the possibilities of what might be the problem.

The only thing I'm unable to advise is the soldering and removal of soldered parts. Not my foray, and I'm thankful I have a friend that does know about these things so he can help me with it. But I know just enough on hardware to find and diagnose a problem and, if it's socketed chips or anything that can be unplugged or plugged in, I can fix that.