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DistantStar001

I'm Getting My First C64, And I Have Questions

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I can't check the schematics for the C64 at this moment, but I would say that C107 is not expendable :D

 

Regarding the ceramic capacitors, I have seen arcade PCBs with lots of them not just chipped but broken, and they were still working. The problem with the board is that it may have some serious problems if some of the capacitors are in so bad state. But I would go with that board anyway: I would place C107 in its place, and check the main and second voltage on 6581 (SID): you should have +5 on pin 25 and +12v on pin 28. If you find this is correct, then you can move to check the ICs; if it is not, you have to take a further look on the supply side.

Edited by deepfb

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OK, so minor update: I put a proper capacitor in C107 and checked the voltages. They all seem good, but I still get a black screen, even on the dead test.

 

A friend loaned me a logic probe and suggested that I should check the clock oscillator, which I did. On my original, and the board that is missing its SID, I get activity on both sides, on the third board (the one that was missing C107) I get activity on the pin closest to C070, but the other is constantly low. My friend recommended replacing the oscillator, which I did, but there's been no effect, as I'm still getting the same readings.

 

Also, on the same board, there is a small green ceramic capacitor bridging C041 and R042 at their nearest leads which isn't there on the other two boards. Does anyone know why that might be there? And should I remove it?

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I can't check the schematics for the C64 at this moment, but I would say that C107 is not expendable :D

 

Regarding the ceramic capacitors, I have seen arcade PCBs with lots of them not just chipped but broken, and they were still working. The problem with the board is that it may have some serious problems if some of the capacitors are in so bad state. But I would go with that board anyway: I would place C107 in its place, and check the main and second voltage on 6581 (SID): you should have +5 on pin 25 and +12v on pin 28. If you find this is correct, then you can move to check the ICs; if it is not, you have to take a further look on the supply side.

 

Chipped is usually ok but I always check their values just in case they're off.

 

I've only had one game ( it was a King Of Boxer ) constantly crash because of missing and broken decoupling caps. Once I replaced those the game was stable.

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