Posted By
JamesC
on 2003-10-19
|  Re: Plus4 stopped working
Sheesh I was really tired last night.... errors all around from me. Ulysses was correct in pointing out that the TED is a 7360 or 8360, not a 7501/8501. And I got the colors backwards on the motherboard resistors and capacitors.
Anyway the TED is in the metal cage and it's marked 7360 or 8360. The 7501 or 8501 processor will be just to the right of that cage. Just to the right of the processor is a 6551; that's the onboard communications chip for the user port. Yes the RAM bank is those small chips in the bottom right corner.
You could also have a problem with the BASIC or Kernal chips, those are U25 and U26 just below the TED's cage. Might also be the PLA, I believe that's the chip in U19. The PLA is the programmable logic chip. It's socketed on the Plus/4 'cause the 64's early production had a lot of those go bad, and the 64's were soldered to the motherboard. By socketing the chip it is field repairable instead of sending the whole motherboard back to Commodore.
One place we know the problem is NOT, and that's the 3+1 software in U23 and U24. Even if those are inserted in the wrong order, or missing completely, the computer will still come on to BASIC.
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