rebeltaz
Experienced Member
Sweet!
It feels great to be able to bring an old system back to life. :D
RAM chips can be piggybacked but I haven't had a lot of luck in doing that to the C64.
If you have a logic probe it'll help you "look" at the signals on the chips and can help you determine which RAMs are bad based on those signals.
It can also help you find bad mulitplexers as well. (The address lines are multiplexed on the DRAM ICs - That's how you can get 16 address lines on a 16 pin chip.)
Also, Commodore used several 74xx logic chips they made themselves. They were stamped with their own part numbers.
65245 = 74LS245
7707 = 7406
7708 = 74LS257
7709 = 74LS258
7711 = 74LS139
7712/8712 = 74LS08
They also had a 7714 which I haven't figured out a cross for yet.
Raymond
I'm not ashamed to say that I was grinning from ear to ear after repairing those systems - kinda like this: :-D
I do have a logic probe or three but I would have no idea what I was looking at. The last time I used a logic probe was probably 20 years ago and that was on circuits that I had built, so I knew what to look for and where....
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Actually, I was just reading through the service manual and I may be able to figure this out after all. And I found a SAMS Troubleshooting and Repair Guide that should help.
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