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Thread: PET won't power on

  1. #1

    Default PET won't power on

    So I picked up a PET 4016 that had been sitting in a storage unit for God knows how long yesterday. Opened it up and things look pretty good overall (lotta dust, but no rust or capacitor leakage.) But when I plugged it in and flicked the switch, nothing happened - even the monitor doesn't turn on. Checked the fuse and that's good, so I'm assuming the PSU bought it. What should I look for to troubleshoot this? I've heard advice that some older PSUs shouldn't be disconnected for troubleshooting as they'll have further issues without a load placed on them - does the PET fall under this category?
    Computers: Amiga 1200, DEC VAXStation 4000/60, DEC MicroPDP-11/73
    Synthesizers: Roland JX-10/SH-09/HS-80/MT-32/D-50, Yamaha DX7-II/V50/TX7/TG33/FB-01, Korg MS-20 Mini/ARP Odyssey/DW-8000/M1, Ensoniq SQ-80, E-mu Emax HD/Proteus-2, Casio CZ-5000, Moog Satellite, Sequential Circuits Prophet-600
    "'Legacy code' often differs from its suggested alternative by actually working and scaling." - Bjarne Stroustrup

  2. #2
    Join Date
    Dec 2005
    Location
    Toronto ON Canada
    Posts
    6,596

    Default

    A lot of things could make it appear dead other than the power supply; unfortunately it's rarely an easy power supply fix.

    The way it is integrated and split up with the capacitor off board you'll have trouble testing it while disconnected; assuming you have a meter you can check the raw AC voltages at the transformer while disconnected, but for the DC voltages you'll have to connect it.

    m
    Last edited by MikeS; April 30th, 2017 at 02:50 PM.

  3. #3

    Default

    Hi

    Is the 4016 a 9inch or 12inch version. I ask as I have a 12 inch which didn't power up. Could be lost of things but found that the Europeans ones, at least, have a small silver mains filter (to reduce interference with TVs etc) that was mounted underneath the transformer and had popped. I bypassed it and all was well (apart from memory issues).

    If not that, does the transformer output any voltage to the board ? Also check for blown capacitors on the board on the voltage regulator side. Zimmers website have great circuit schematics to help you.

    Cheers

  4. #4

    Default

    It's the 9" model. I haven't gotten around to serious testing, but I did pull the board out and take a better look at it - none of the caps on the main board look blown, but I don't actually know how to test them aside from a basic continuity check with a multimeter (which they passed.) Haven't checked voltages out of the PSU or anything yet.
    Computers: Amiga 1200, DEC VAXStation 4000/60, DEC MicroPDP-11/73
    Synthesizers: Roland JX-10/SH-09/HS-80/MT-32/D-50, Yamaha DX7-II/V50/TX7/TG33/FB-01, Korg MS-20 Mini/ARP Odyssey/DW-8000/M1, Ensoniq SQ-80, E-mu Emax HD/Proteus-2, Casio CZ-5000, Moog Satellite, Sequential Circuits Prophet-600
    "'Legacy code' often differs from its suggested alternative by actually working and scaling." - Bjarne Stroustrup

  5. #5

    Default

    You won't fry the power supply by running it unloaded; it's a good olde fashioned linear supply. Do check it first.

    The monitor won't get a raster if the logic board (PET computer part) is not doing what it's supposed to, which it likely isn't. But do start with checking the power supply. In the meanwhile, it may be best to unplug the connector on the mainboard that leads to the monitor.

    I wish I had time to write a summary of the procedures we end up using here for PET repair. Start with the power supply, next probably reseat all the socketed chips, then check the clock generator.

    If you have close neighbors, for their sake, please don't run without that mains filter, if you can avoid it (that is, replace it when it dies), as running without it can cause unlawful (here in the States, but still most likely won't get you in trouble) at worst, and discourteous at best radio interference. These days, dwellings are teeming with devices that do this, but it's still best to squash it wherever you can. Depending what kind of wireless devices you have (including digital TV), generating RF interference could be wreaking havoc for yourself, and you might not even know why.
    Be polite and I may let you live.

  6. #6

    Default

    Ok the 9inch ones don't have the extra filter ... so guess it will be down to basic detective work. This forum has lots of examples of where to start looking and reseating chips and measuring the voltages are correct is a start .... wish could be more helpful.

    I run my PET's off dedicated mains filters to reduce the effects of mains spikes and interference.

  7. #7

    Default

    Well, the only socketed chip is the 6502 itself, and removing that and reseating it didn't solve the problem, so yes, I guess it's down to detective work...

    If nothing else, this'll be a good learning experience
    Computers: Amiga 1200, DEC VAXStation 4000/60, DEC MicroPDP-11/73
    Synthesizers: Roland JX-10/SH-09/HS-80/MT-32/D-50, Yamaha DX7-II/V50/TX7/TG33/FB-01, Korg MS-20 Mini/ARP Odyssey/DW-8000/M1, Ensoniq SQ-80, E-mu Emax HD/Proteus-2, Casio CZ-5000, Moog Satellite, Sequential Circuits Prophet-600
    "'Legacy code' often differs from its suggested alternative by actually working and scaling." - Bjarne Stroustrup

  8. #8

    Default

    Must be a very late model!
    Be polite and I may let you live.

  9. #9

    Default

    Late enough that it's one of the ones where they punched holes out of the board by the additional RAM sockets because people were upgrading the RAM themselves rather than buy a 32KB model
    Computers: Amiga 1200, DEC VAXStation 4000/60, DEC MicroPDP-11/73
    Synthesizers: Roland JX-10/SH-09/HS-80/MT-32/D-50, Yamaha DX7-II/V50/TX7/TG33/FB-01, Korg MS-20 Mini/ARP Odyssey/DW-8000/M1, Ensoniq SQ-80, E-mu Emax HD/Proteus-2, Casio CZ-5000, Moog Satellite, Sequential Circuits Prophet-600
    "'Legacy code' often differs from its suggested alternative by actually working and scaling." - Bjarne Stroustrup

  10. #10

    Default

    Simple enough to get around that! I always wished (back when those were still commonly in use) that I could afford one so I could add RAM to it.
    Be polite and I may let you live.

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