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Thread: PET 8032? dead.

  1. #21
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    Quote Originally Posted by daver2 View Post
    So, to my knowledge, any of the parts you have identified should be fine.
    Dave,
    That is correct. There are some different capabilities between the Motorola and Rockwell, but none that the Commodore uses.

    To Twist: I would hold off on the CRT Controller until we prove the CPU is running and there is still no CRT timing signals. I'm betting on a bad ROM and then a bad zero page RAM. Are your ROMs on sockets?
    -Dave

  2. #22
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    Quote Originally Posted by daver2 View Post
    It looks like you have no H. Synch.

    I would suggest trying the piggyback RAM test first then if the original owner suggested that may have worked. If you have a RAM problem - then you need to fix that first...

    Dave
    Done. Got some 4116 RAM and piggybacked. I made sure the pins were tight on there(and hopefully scraping off oxidation?) Same situation on all 8 chips. I could piggyback all at the same time. Is it safe to piggyback a CRTC?
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

  3. #23
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    Quote Originally Posted by twistedpneumatic View Post
    Done. Got some 4116 RAM and piggybacked. I made sure the pins were tight on there(and hopefully scraping off oxidation?) Same situation on all 8 chips. I could piggyback all at the same time. Is it safe to piggyback a CRTC?
    After piggybacking a RAM, did you cycle power to see if anything changes? You have to do it one at a time for all eight low RAM chips (UA5,7,9,11,13,15,17 and UA19). If you get even a hint of a change, that's the bad chip.

    If no changes, check the 6502 Sync signal (UB14-pin 7) to see if it is pulsing (~1.3 V) for a 25% duty cycle pulse. If stuck at zero Volts or ~5 V, the computer is not fetching instructions. It may be a bad ROM. Check the four highest address lines (A15 to A12) to see where it is stuck. That may tell you what ROM is bad.

  4. #24
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    No sign of change on the second pass. Turn off->change piggyback->turn on. Nothing. SYNC is 0V.
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

  5. #25
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    Quote Originally Posted by twistedpneumatic View Post
    SYNC is 0V.
    This is an indication that the 6502 is stuck and not fetching instructions. It is sometimes caused by a ROM with bad data content. The CPU reads an illegal OP Code (instruction) nicknamed a 'KILL' instruction, and hangs up. Use meter to determine state of A15 through A12. If upper address lines read, for instance, all 5V (1111) that implies the computer is stuck in the $FXXX address range and the bad ROM may be the kernal ROM UD6.

  6. #26
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    Quote Originally Posted by dave_m View Post
    This is an indication that the 6502 is stuck and not fetching instructions. It is sometimes caused by a ROM with bad data content. The CPU reads an illegal OP Code (instruction) nicknamed a 'KILL' instruction, and hangs up. Use meter to determine state of A15 through A12. If upper address lines read, for instance, all 5V (1111) that implies the computer is stuck in the $FXXX address range and the bad ROM may be the kernal ROM UD6.
    All read 3.53V
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

  7. #27
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    Update: I happened to notice something when I pulled out the board. Seems to have a tiny burn mark near the ROM chips on the bottom. Pics below.

    20180606_204611.jpg20180606_204619.jpg20180606_204629.jpg20180606_204648.jpg
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

  8. #28
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    It looks like someone tried to touch up the solder joints there and left a lot of rosin flux. Clean the area with isopropyl alcohol and check that there are no solder splashes shorting adjacent solder pads.

    If you like to solder, you may have to replace some ROMs with 24 pin sockets and 2532 EPROMs. Otherwise you might consider replacing all RAM and ROM with a small board that fits neatly into the CPU socket. See this link: Tynemouth . There are other vendors of these type of boards as well. Note that while most of the time dead PETs are due to bad ROM or RAM, there are other things that can cause this, but will be hard to find without a oscilloscope.

  9. #29
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    Quote Originally Posted by dave_m View Post
    It looks like someone tried to touch up the solder joints there and left a lot of rosin flux. Clean the area with isopropyl alcohol and check that there are no solder splashes shorting adjacent solder pads.

    If you like to solder, you may have to replace some ROMs with 24 pin sockets and 2532 EPROMs. Otherwise you might consider replacing all RAM and ROM with a small board that fits neatly into the CPU socket. See this link: Tynemouth . There are other vendors of these type of boards as well. Note that while most of the time dead PETs are due to bad ROM or RAM, there are other things that can cause this, but will be hard to find without a oscilloscope.
    I bought sockets to put directly on the PET board and I have the tools to do it. I'll wash off the flux later.

    Question: look at PIC 3 of my previous post. There is a short between those two pins but it looks like the pin was bent. Could that be the issue or do PET's come like that factory?
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

  10. #30
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    Quote Originally Posted by twistedpneumatic View Post

    Question: look at PIC 3 of my previous post. There is a short between those two pins but it looks like the pin was bent. Could that be the issue or do PET's come like that factory?
    I can't tell for sure, but there looks to be a problem there. Move that pin away from the other pad and clean the area. Find out if there is a trace between the two pads. Is it possible to identify the two pins so we can check on the schematic? You may be on to something. Good work.
    -Dave

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