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Thread: Atari 800 (not XL) ROM slot problem

  1. #1
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    Default Atari 800 (not XL) ROM slot problem

    I think I posted about this a while back. I used to frequent a computer store in Vancouver called Cal's, and they had a computer museum in the front of their store that I always enjoyed having a walk through. At some point Cal's went out of business or moved, and the museum was sold off. I managed to grab a few pieces including this original Atari 800. It didn't have the power supply and I forgot about it for about 20 years.

    I got the power supply recently and fired it up and found I was only getting a blank screen. After fiddling around with the RAM and ROM boards I did manage to get Memopad and BASIC but it was very touchy. I tried cleaning the ROM slot with pure alcohol and a little wiper but that made it worse. Presently all I get is a white screen, unless I press down with considerable force on the ROM cart, in which case the screen might turn to black or red.

    I suspect the ROM slot is the problem. I've removed the motherboard and shielding and have carefully inspected all of the traces. I see nothing amiss and the random connections I've tested all come out good. I tested all of the voltages at the header that connects the two mainboards - that's fine. Also seeing the right voltages at the socket pins.

    My question is this... does it matter which slot the ROM cart is installed in? To my eye it looks like all of the slots are wired the same way and I don't see any warning against putting the ROM cart in any of the others. I just want to see if the machine behavior changes as I know some of the other slots are better off.

  2. #2
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    I really don't know if the RAM and ROM boards have to be in designated slots, but to take the machine to it's maximum REAM of 48K you need all of the slots. I would use a pencil erasure to clean the edge connectors of the RAM and ROM boards. I would also recommend rocking the individual chips in their sockets.

  3. #3

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    The 800 does have assigned slots

    Front to back
    Keyboard,
    Right & left cartridge slots,
    CPU (inside case,),
    ROM
    RAM
    RAM
    RAM

    I'd recommend start off with 1 ROM in the first slot and 1 RAM card in the second (next)

    I'm betting there is probably corrosion on the chips. So it may need a bit more work.

  4. #4
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    Quote Originally Posted by ncherry View Post
    The 800 does have assigned slots

    Front to back
    Keyboard,
    Right & left cartridge slots,
    CPU (inside case,),
    ROM
    RAM
    RAM
    RAM

    I'd recommend start off with 1 ROM in the first slot and 1 RAM card in the second (next)

    I'm betting there is probably corrosion on the chips. So it may need a bit more work.
    Thank you.

    I've had a look at the chips... removed, inspected and reseated.. they are gleaming silver... not a hint of rust anywhere. I bought a second 10K ROM card, checked all the chips on it.. same deal. Neither work. If I leave the ROM card out with RAM in stuff happens on screen (just random crazy stuff, as you'd expect). But once the ROM card is in it's a solid white screen unless you *really* press down on it. And even then you don't get the normal Memopad, etc. Just Black, or maybe very dark red.

    I think getting to the connector pins deep down might help. I just haven't figured out a way to do that. I am wondering if some of the pins have sort of recessed into their grooves and aren't making full contact with the card anymore.

  5. #5

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    The Atari 800 had five motherboard slots plus two smaller cartridge slots for games/programs. Starting from the back of the machine, the larger slot holds the CPU card. The next three would hold the memory cards and the last slot would hold the personality card (System ROM/Notepad). In this configuration the machine has no Basic installed. A Basic cartrige has to be installed in the left hand smaller cartridge slot and the machine re-booted to the Basic prompt.

    As far as I know, I have only seen the personality board in slot 5 (from the back of the machine) and only slots 2,3 and 4 used for memory and in fact, these were the only slots accessible to the normal user along with the two game cartridge slots.

    If you are getting different results when you apply pressure to the cards and/or motherboard I would look closely at the solder points of the slot connectors looking for a cold or broken solder joint as you gently flex the board/cards.

    Then I would clean and reseat the socketed chips on the personality card (if any) and try again with the CPU card, one memory card and the personality board. Cycle the three memory boards to see if one is defective. The Atari 800 will work with one 16K card.

    Since you said the machine worked once, the components are probally good with only mechanical problems with all the connectors.

    Take a look at the [Atari 800 Service Manual] at "www.atarimania.com/documents-atari-400-800-xl-xe-technical-documents_3_8.html"

    Charles

  6. #6

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    Oh, right, the CPU (Personality) is in the back. Sorry. I haven't had to open mine recently and I've got more than a few computers stored in my memory

  7. #7
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    If there is a cold solder joint I cannot see it. I could put the soldering iron to the pins underneath and 'reflow' the solder. It seems to me that on my first run, the only thing that got it working was cleaning and finagling the rom card and having 1 ram carr installed. Then I tried to clean the slot pins more as I found it still wasn't reliable. When I did that that was it... it never worked again.

  8. #8
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    Okay.. I took the motherboard right apart.. so far everything's checking out with the multimeter. I'm probing the pins of the ROM card and the bottom of the socket pin on the other side.. they're all getting good connections.there's a few TTL that were a bit loose but.. yeah.. so far.. it's all looking ok. Scratching head.

  9. #9
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    Another thing I'm curious about.. what's the deal with the handwritten 'serial'?

    20190123_215236.jpg

  10. #10

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    Falter

    After looking at all the schematics for the Atari 800 the slot connector for the "Personality module-J107" is very different from all the other card connectors on the machine. So there is no chance of the per. module working in any other slot than J107. To complicate matters, Atari used alphanumerics instead of pin numbers to identify connections in the card slots making it very hard to trace.

    If your goal is to just get the Atari working, it might be cheaper/faster to buy just a 800 motherboard on Ebay ($14.99+$10.26 US ship) and swap out the LSI chips (POKEY etc). The 22/44 Pin Connectors do not seem to be common on Mouser or DigiKey so I don't think you can unsolder the J107 connector and replace it if it turns out to be a problem.

    Since everything checks out physically and electrically, I would look at the things that make J107 different like the decoding for the ROMS G and *G as well as the signals S4,S5,S6,S7 and A15...there may be others. Try to trace them back to TTL components looking for a bad trace or even a bad component.

    The schematic I used is downloadable from "www.jsobola.atari8.info/dereatari/literatdere/400_800sm.pdf" and is very readable.

    Good luck on repairing the Atari 800; it was my first computer and I still have it in working condition.


    PS- I don't know about the serial number...mine is printed on the bottom label (#41559

    >>> Charles

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