Need a clean image of a C64 250425 PCB

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DistantStar001
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Need a clean image of a C64 250425 PCB

Post by DistantStar001 »

So getting down to it. I've been trying to repair a 250425 C64 board for a few years now. It worked when I first got it, then stopped. And over the years, tracing various faults, and replacing literally every single IC, all I get is a black screen (even on dead test). Suffice it to say, the thing has more than a few broken traces. Some my fault, while others seem to be due to the age of the board. Even so, I've resolved to fix this thing.

To that end, I've decided to "start over" by removing and replacing every socket so I can see and trace every damaged trace. So far it's working. However, I have no idea where some of the missing traces go (since there missing and all). To add to my troubles, I'm not great with schematics. What would really be helpful, would be an image of the unpopulated board, with a high enough resolution that I can make out all the traces.

I've been trying to work from images on the internet. But most are of those are of populated boards, which doesn't help as many of the components are covering the traces. And for the few unpopulated images, the few I've found are at odd angles or of such low resolution that I can't make out the traces.

So I'm putting it out there. Does anyone have some high res images of the PCB they can post or send me? Or an unpopulated replica of the 250425 they can scan?


banman
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Re: Need a clean image of a C64 250425 PCB

Post by banman »

Hi DistantStar001,



Sounds like you have a great deal of patience, that will definitely help you in testing.
I had a similar situation.
I once found when trouble shooting a C64 board the actual rocker power switch was not making good contact. I would always test good on all the various voltages around the board as one would expect. However the board wouldn't start up.
It took me ages to realise this. At first I thought it was the PLA or both the voltage regulators.
I desoldered everything off the board. All IC's including the RF modulator (which was a real pain).
It was only by chance after I had removed everything off the board and I was testing current flow around the RF modulator area on the bare board that the issue became apparent.

After determining this. I used a bit of lubricant and elbow grease and worked the power switch till it came good. Maybe about a good 5 minutes worth of switching.
So maybe a good hard look at the power switch is in order.

I also use this particular Commodore factory service manual troubleshooting routine.
I found it to be better that some of the others.

Have a look at this thread for details.

viewtopic.php?p=18856&hilit=Troubleshooting#p18856




It always a satisfying feeling getting back to rights a C64.

Let us know how you go with your repairs. :D
DistantStar001
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Re: Need a clean image of a C64 250425 PCB

Post by DistantStar001 »

I've actually made some progress today! Going over the board, I've managed to locate and patch 8 broken traces on the board, and have begun repopulating it with machine sockets. In hindsight, maybe I should have slipped in a few zifs for future testing, but I wasn't sure that the board would be salvageable until now.

In any case, I've re-socketed all the logic and ram, as well as the CPU, PLA, SID, VIC II, Timer, one of the CIAs, and the Character ROM. I intend to do the rest as soon as I can get some quality sockets. In the interim, however, I do have enough socketed to try a dead test.

I've been getting a single flash indicating a RAM issue. Believe it or not, that's a huge improvement over the stubborn black screen I had before. It means that the dead test is actually booting! I've tried swapping out the indicated RAM (U9, U12, and U21) but so far no luck. I started with U9 (meant to do U12, but whatever). After that, I got six flashes. Replaced U22, and got five. Swapped U10, and I'm back to one. It's possible the RAM I have is bad, so I'll probably have to get some new chips, but I'm definitely getting somewhere! :-)
banman
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Re: Need a clean image of a C64 250425 PCB

Post by banman »

Hi DistantStar001,


That's very good work.
I try to ground myself when swapping out ram chips. I have damaged some in the past by not taking extra static protection precautions. :D
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