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Thread: cbm 8032 rusty and dead

  1. #21
    Join Date
    Feb 2009
    Southern California, USA


    Quote Originally Posted by Xchip View Post
    But I found another problem, the cpu signal on the PIN17 signal AB8 is abnormal, it could be a short circuit or a defective chip but I have not yet understood where the problem is, I have already replaced on that line a 74ls244 and a 7425 without success
    The source of address line 8 signal (AB8 ) is the CPU (UB14), but the 6502 chip rarely fails, and you say you replaced the buffer at UD14 (74LS244). If you have another 6502 CPU then try replacing UB14, but the problem may be an intermittent short on the AD8 line caused by solder splash, bad solder joint, bad IC socket, etc. Look with magnifying glass and if nothing found, reflow the solder joints on socket UB14 or replace socket. You are doing good!

  2. #22


    after so much work I found two broken logic chips: 74ls02 and a 74ls00 that were partially working. the current situation is that on the video an unstable image appears with some dots but nothing readable, every reset always performs the same thing so the computer must be working because the CRTC is programmed by the CPU and starts the video signal generation, with good probability I made a mistake or some capacitor is at a loss as I have already verified several times, if you have useful suggestions to check the signals with the oscilloscope I am grateful.
    now I'm close to the solution of this unfortunate computer.

  3. #23


    The CRTC running indicates that the CPU got far enough to initialize the CRTC. It may or may not be working after that. The processor is likely good but you may still have a problem with RAM or ROM.
    Some pictures of what you have would help to know where to start looking. A better indication of the processor working correctly would be for you to type in a proper command and see if the command does anything to the display? It doesn't have to display correctly, just respond in some way. That would help to isolate a display problem from a code problem.


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