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Thread: PET 8032 Resurrection Help!

  1. #11
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    Quote Originally Posted by daver2 View Post
    Looking at your ROM set - it is not that you have a device missing from UD12 ($9xxx) - you have gained an extra device at UD11 ($Axxx) - the one with the white dot! I wonder what that is?

    Can you identify what is actually marked on each and every ROM you have in the machine and we may/should be able to identify what is actually in there.

    Dave
    PSI-5054?
    wordpro-a000.bin
    ROM for the Wordpro word processor for the PET. This is a mask programmed ROM labeled PSI-5054 and is located at $A000. It is used for version 4 and 5 of Wordpro. Version 3 did not require a ROM.

    Which, by the way- I have the 64k RAM board removed. I wonder if I need to change any jumpers or anything so the machine will work properly without it?
    Last edited by rittwage; December 20th, 2018 at 09:06 AM.

  2. #12
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    >>> ROM for the Wordpro word processor for the PET.

    Ah, that explains it.

    >>> I wonder if I need to change any jumpers or anything so the machine will work properly without it?

    I shouldn't think so.

    Dave

  3. #13
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    OK, I burned the PETTEST ROM to a 27128 (copying the data over and over up to 16k) and used one of Jim Brain's 28 to 24 pin adapters. It shows nothing on the screen still...

  4. #14
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    Probably the CRTC or monitor.

    Do I remember reading in one of your posts that you have an oscilloscope?

    If so, time to break it out...

    We are going to measure the video, horizontal and vertical synch signals generated by the CRTC. These are all 5V signals - so 1V/cm vertical is good.

    Hopefully dave_m will chip in and help out. I am off to bed!

    Dave

  5. #15
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    PETTESTE2KV03 does not need much of ROM and no RAM to run. It only needs the first few instructions in the kernal ROM ($F000) after the Reset Vector is loaded to work correctly then it takes over. It in initializes the CRT Controller. As daver2 mentioned, you need to see that there is a good Horizontal signal (20 KHz) coming the the CRTC and a good 60 Hz Vertical signal in order to get high voltage in the CRT and to get a raster scan. See schematic http://zimmers.net/anonftp/pub/cbm/schematics/computers/pet/8032/8032029-10.gif .

    All this assumes that you don't have a short on the address or data lines, but first things first. Remember the chirp indicates that you can execute at least some instructions, so let's assume for now that there are no critical shorts.

    If it turns out you have good CRT timing signals, then there may be a problem in the CRT Video board. If there are no timing signals then the 6545 CRT controller chip may be bad. We should also check some key CPU signals like Sync and Reset. Sync will tell us if the CPU is continuously fetching instructions, and we need a clean Reset at power up for anything to work properly. Some troubleshooting ahead is necessary.

  6. #16

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    Guys

    Just a few thoughts

    Does your tester chip check the Big chips - in particular the 6520's, or works OK when one is faulty ?
    I have had a couple of boards with faulty 6520's that hold an address line high (for example). The PET would chirp but not do anything else.

    Also check the outputs on the 74154 to see if that is faulty etc. ... schematics are on Zimmers...



    Not wanting to digress from above,
    >>>I wonder if I need to change any jumpers or anything so the machine will work properly without it?<<< - the extra 64k board is enabled and accessed entirely through software. Once your PET is up and running, there is a burnin program you can run to check it out. I followed the procedure documented on http://www.primrosebank.net/computer...rs_ext_ram.htm
    Last edited by AndyG; December 21st, 2018 at 12:09 AM.

  7. #17
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    Thanks guys, I will break out the scope and make sure it's still running. I have family coming tonight and staying for a couple of days, so it may be Sunday evening until I can look at it unless there is some free time.

    I assume I will measure the signals at the pin connector leading up to the display...

  8. #18
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    Yep, disconnect the monitor connection to the main board and measure at the connector on the main board.

    As Dave (M) has already stated, we suspect that the Kernal ROM $Fxxx is fine (as is the Edit ROM at $Exxx) as you get the initial 'beep' at power-up.

    We are in a catch-22 situation for the 'big chips'. The keyboard PIA is checked by my tester, and the IEEE and VIA will be on the next release. However, if they have failed sufficiently for the test ROM to not even start-up then we have a problem. My test ROM requires the CPU, clock, $Fxxx and $Exxx ROM and decode plus the address and data bus to be in operational order. I don't require the RAM to be working, nor the bulk of the BASIC ROMs (I checksum these as part of the test).

    What we could do with is an initial 'sticky' post identifying all the initial steps to resurrecting a PET...

    Dave

  9. #19

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    Quote Originally Posted by daver2 View Post
    Yep, disconnect the monitor connection to the main board and measure at the connector on the main board.

    As Dave (M) has already stated, we suspect that the Kernal ROM $Fxxx is fine (as is the Edit ROM at $Exxx) as you get the initial 'beep' at power-up.

    We are in a catch-22 situation for the 'big chips'. The keyboard PIA is checked by my tester, and the IEEE and VIA will be on the next release. However, if they have failed sufficiently for the test ROM to not even start-up then we have a problem. My test ROM requires the CPU, clock, $Fxxx and $Exxx ROM and decode plus the address and data bus to be in operational order. I don't require the RAM to be working, nor the bulk of the BASIC ROMs (I checksum these as part of the test).

    What we could do with is an initial 'sticky' post identifying all the initial steps to resurrecting a PET...

    Dave
    Yes - it is a dilemma. I have found the diagnostic board from Tynemouth extremely useful in identifying stuck address and data bus lines, bad video ram, normal ram and roms etc. It too doesn't look at the "big chips", most of which are usually soldered in on the Universal Board and it has been a little bit of a lottery to identify the bad one (though desoldering and adding sockets is not that difficult). . I spoke to Dave at Tynemouth about it also and its not trivial.... These PETS do like to fail in all sorts of weird and wonderful ways.

    Agree with the idea of creating a crib sheet to work from for other users who have bad PETS (The Tynemouth software Blog contains a lot of extremely useful information from his repairs)

    Cheers
    Andy
    Last edited by AndyG; December 21st, 2018 at 05:47 AM.

  10. #20
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    I have tried pressing all the keys hundreds of times and I never get any more beeps or chirps. Unfortunately, as you mention, none of the "big" chips on mine are socketed, so I may have to socket the board.

    That is not a problem for me, just a couple hours of work, but I probably should get spares for the 6520's, 6522, and the CRT controller in case they have to be destroyed, though.

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