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Thread: My PET in a suitcase has stopped working

  1. #1

    Default My PET in a suitcase has stopped working

    Hi all,
    I'm back. I'm sure many of you recall the epic thread where we fixed both my 2001 motherboard, and the 2001 motherboard for my PET in a suitcase.
    Well, I went to power on the PET in a suitcase the other day and boot screen appeared, although after a few seconds strange things stared to happen. The cursor became unresponsive, and some of the characters became corrupt. I did a power cycle and the problem was worse. after a few power cycles the screen looked like this:

    PET.jpg

    The suitcase PET has a Nick Welte RAM/ROM board (I also have one in my full PET 2001). At first I thought maybe it was an issue with this, but I swapped the RAM/ROM units between the machines and that both work fine.

    I replaced the two video RAM but that didn't change anything.

    As a simple test I then pulled the video RAM expecting to see the typical checkerboard, but instead I saw this.

    No video RAM.jpg

    ...it's constantly moving busy mess of pixels.

    Well, that's where I'm at now, Just wondering if anyone had any thoughts or ideas on what I could test next.

    Thanks (again)

    Philip

  2. #2
    Join Date
    Dec 2005
    Location
    Toronto ON Canada
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    7,137

    Default

    Well, the obvious candidate would be the character generator and associated shift register, but that wouldn't explain the dead cursor.
    I'd start by checking the +5V power (the connector is a notorious trouble spot) and replacing the character generator IC anyway.

  3. #3

    Default

    I say we start from ground zero here. What kind of suitcase is it? Obviously we'll need some pictures Kidding aside, I think Mike's on to something with the voltage issues.
    Looking to acquire: IBM 5100, Altair 8800

  4. #4
    Join Date
    Dec 2005
    Location
    Toronto ON Canada
    Posts
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    Default

    Quote Originally Posted by barythrin View Post
    I say we start from ground zero here. What kind of suitcase is it? Obviously we'll need some pictures
    You mean you missed this epic PET saga where Philip earned his stripes?

    http://www.vintage-computer.com/vcfo...light=suitcase

    See post #199; unfortunately it looks like you have to log into the iCloud to see the pics.

  5. #5
    Join Date
    Sep 2011
    Location
    Napa, CA, USA
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    Blog Entries
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    Default

    Is it possible for anyone to upload those images elsewhere? Just having an account won't let you view them unless you also have iCloud setup on a device - something I don't have.

    http://www.vintage-computer.com/vcfo...729#post182729

    Edit: It seems they're dead links, as I was told by someone else who has a device setup with iCloud.
    Last edited by Compgeke; November 12th, 2013 at 10:49 AM.

  6. #6

    Default

    It's not the character generator because you can see characters. The character generator is simply a ROM and if corrupt the characters wouldn't look correct. The video circuit appears to be working correctly as it is normal to have garbage on the screen before the system clears the video memory. I would focus on the CPU logic. I see you swapped RAM/ROM which contains the CPU, did you swap CPU's with it? I had an issue with mine in my 2001 where it wasn't seated correctly and made the same screen. Check your voltages but I'd look more closely at the RAM/ROM board even though you swapped it. Check the rest of the board for rising chips, simple enough to just give a good push to them all to make sure they are seated correctly.
    Briel Computers
    retro hobby kits
    http://www.brielcomputers.com

  7. #7
    Join Date
    Dec 2005
    Location
    Toronto ON Canada
    Posts
    7,137

    Default

    Quote Originally Posted by vbriel View Post
    It's not the character generator because you can see characters. The character generator is simply a ROM and if corrupt the characters wouldn't look correct. The video circuit appears to be working correctly as it is normal to have garbage on the screen before the system clears the video memory.
    I did say that although it might be the first thing one thinks of since just because the @ is OK the rest could be corrupted, and the second screen certainly doesn't look like "normal garbage" or correct characters, it probably isn't the problem and wouldn't explain the dead cursor; still, since it's socketed and he has a spare it couldn't hurt. A screen of @s usually indicates a stuck bit in the video RAM section, but that doesn't explain everything either.

    AFAIK you can remove all the RAM and ROM and still get the 'normal' garbage screen; mine isn't accessible right now or I'd see just how many ICs you can remove and still get a checkerboard display.
    Check the rest of the board for rising chips, simple enough to just give a good push to them all to make sure they are seated correctly.
    Good advice if he hasn't already tried that.

  8. #8

    Default

    Thanks for all the replies. Let me try to answer as many questions as possible.

    - Firstly, all those pictures were uploaded to Apple's .mac service via iWeb which is now dead and replaced by iCloud. It seems the link is just redirected to iCloud.
    fortunately I still have iWeb as I still use it to build my neoncluster.com page, and I still have archived the data for the now broken link. I have re-uploaded everything here:
    http://www.neoncluster.com/projects-pet/2001-Fix.html

    and you can read a review of the fix here:
    http://www.neoncluster.com/projects-...001repair.html

    - Yes, when I moved the RAM/ROM board I also moved the CPU with it. In fact I've even replaced the CPU with another spare just to be sure. Although one issue maybe that the RAM/ROM board is not making good contact with the socket. These sockets are very dodgy, to say the least. I've wiggled things around and reseated every IC that is socketed. Most IC's however are not socketed.

    - The character EPROM is a replacement 27xx mounted on an adaptor, I'm pretty sure this is ok. I've pulled it, and I get mostly an all white screen, but with some weird artifacting, missing pixels etc.

    Next I'll check out the 5V power.

    Thanks again

    Phil

  9. #9

    Default

    Oh...and here is a pic of the suitcase:

    Suitcase.jpg

  10. #10

    Default

    Woohoo!! Thanks for the pic I would have thought the dead CPU would result in properly rendered but random graphics if the reset was failing. I suppose I'm not 100% familiar with PETSCII though but the pic above sorta looked like malformed characters? You have just enough room in that suitcase for a sony watchman or something for video output ;-p
    Looking to acquire: IBM 5100, Altair 8800

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