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Thread: Model 100 No power up

  1. #1
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    Default Model 100 No power up

    I got one of these for nothing, and have been checking it out this morning. The battery compartment had a significant but not crazy amount of rust, which I've since cleaned. I can see just under 6V there.

    I also see a NiCD battery on the motherboard. When I tested it of course, it had close to 0v.. but after letting it sit with the AA batteries installed, it has risen to 1.6V. Do I need to wait this out a bit? I'm not sure if the 100 requires the NiCD to get going. I don't think my 600 did.

  2. #2
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    The NiCD has risen to 3.3V now. I'm surprised I'm getting anything.

    I guess the AAs charge it?

  3. #3
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    Okay, the NiCD seems to be charged and holding a charge. But no action otherwise from the machine. I was checking out the voltages on the motherboard at various points like VEE - and we've only got +0.87v on power up. So I'm going to guess we've got cap problems, problems with the battery holder/connection or such. Wish I had the power adapter.

  4. #4
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    If it helps, the power adapter is 6VDC @ 400 mA. The batteries will charge the NiCd battery which feeds the memory to maintain it while not in use. There's a switch on the bottom; make sure it's "On"

    You did try to change the LCD contrast knob? Sometimes it looks blank and just need adjustment.

  5. #5
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    Yeah it's not that for sure. When I was playing around with the batteries and cleaning the contacts, I noticed sometimes the 'low batt' light would come on, even though the batteries were brand new. It looks like the board has some significant corrosion damage, although so far traces look to have been spared.

    As a side note.. does anyone know the serial number scheme they used? I think this may be a very early one:

    20191012_171435.jpg

    Looking through a bunch on line, it seems they all start with a 3. I've not seen any lower than 301xxxxxx, (they seem to go up to 304xxxxxx) and mine is 301000089. All the chips on mine are date coded to mid 1982... that'd be really neat if I managed to luck out and by an early one. Not that that means much with these.

  6. #6
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    If you were after the original, why not look for the Kyocera 85? After all, Tandy didn't design or initially produce this thing.

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    Quote Originally Posted by Chuck(G) View Post
    If you were after the original, why not look for the Kyocera 85? After all, Tandy didn't design or initially produce this thing.
    I can vouch for the Model 100's reliability as mine is 34 years old (1985) and still working.
    Surely not everyone was Kung-fu fighting

  8. #8
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    Quote Originally Posted by Chuck(G) View Post
    If you were after the original, why not look for the Kyocera 85? After all, Tandy didn't design or initially produce this thing.
    I wasn't actually trying to get original. I was trying to get cheap. A few of these were up on ebay from same seller.. one worked but had broken screen, this one did not work at all but looked clean and physically good shape, and I thought I could probably fix it.. and it was $10. I'm just curious if I lucked out and got an early one.. I don't know what their scheme was for serials.
    Last edited by falter; October 12th, 2019 at 06:29 PM.

  9. #9
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    The first digit is the year (1983 or 1984) and the next two are the month; somewhere around October 1983 (310xxxxxx) the board was changed to use a JEDEC 'standard' 27C256-compatible system ROM instead of the non-standard ROM used in the early models.

    There were two models: 26-3801 with 8K RAM, and 26-3802 with 24K RAM, both with sockets to expand RAM to 32 K using non-standard 8K modules.

    Corrosion around the main & backup batteries and bad caps are probably the most common hardware issues, videos and cap lists are out there; you might want to join the Club100 mail list at bitchin100.com, lots of smart and helpful folks there.

    Have fun!

  10. #10
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    Thanks Mike.

    That's interesting.. so 301 would be January 1983. So 301000089 would imply this is the 89th unit (since there weren't any earlier than 1983)? That'd be pretty cool.

    Yeah so far this is looking like a basic corrosion problem - I can see 5.7V at the battery terminals, but only 0.87V at the various ICs when powered on. The service manual says to check the transformer, which I am figuring out how to do as the pins are on the opposite side and I have to get power there somehow. I'm tempted to just direct solder a 6V power adapter I have and skip the batteries altogether until I have it working.

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