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Thread: Model I - Things to check before applying power?

  1. #11

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    An update, now that I've received the parts of make a composite video cable - it works!

    trs80-8.jpg

    Don't judge me too harshly for using the monitor from my Apple //c -- it's the only monitor I have at the moment which accepts composite in.

    I've only powered on the base unit, to verify that it works. My 14 year old son is now experimenting with it.

    In the next few days, I'll test the Expansion Interface. I'll need to source a Model 1 floppy before I can test the floppy drive.

    -Kevin

  2. #12

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    In the process of my youngest doing some work on the Model 1, we've discovered that the video goes unstable after a bit. It appears to be purely a horizontal stability issue and if we leave it unplugged overnight, it works for a few minutes the next day. Here's a short video of what it looks like:

    [video=Here's a ]https://vimeo.com/279917658[/video]

    In doing some poking about online, I'm guessing it's a problem with Z5 or Z6. I've found a video of a repair of a system with similar problems.

    I've got a friend who's very handy with electronics who I'm going to have help me with the diagnosis and repair - while I can solder, he's much better at it than I am, and I'd rather not muck up the board. Once we know what the bad part(s) are, the ICs will get replaced with sockets and appropriate chips plugged into them.

    His suggestion was, since it works for a little while, starting with a can of freeze spray since it's likely temperature-related.

    Any input would be greatly appreciated.

    -Kevin

  3. Default

    That last image looks like a light pen.

    I made one in the 80's for my BBC micro using a Honeywell sweet spot transistor.

    Worked too !

  4. #14

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    Fixed a few Model I units myself with a can of freeze spray. I think your friend's suggestion is a good one. You can also just feel the devices and look for one that's warmer than the others, but freeze spray is better. Use static precautions.

    You have verified that your monitor is OK?

    Good luck with it!

  5. #15

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    You have verified that your monitor is OK?
    Fair question. I should probably test it, though I had the same results with two monitors, one of which we used recently with an Apple //c without difficulties.

    -Kevin

  6. #16

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    Because shipping can be annoying, I want to order both freeze spray and possible replacement parts in one shot - the parts are cheap enough that I'm willing to spend $2 or $3 and order parts I may not need, in order to avoid an extra $10 shipping charge.

    It appears I have a horizontal sync issue, so I want to order likely parts that will repair this. I'll also get a can of freeze spray so that we can test chips before randomly desoldering and replacing.

    That said, I'm looking for input on confirming that I'm looking at replacements that will work.

    Z5 is a 74C00N, so I think this is the correct replacement: https://www.digikey.com/product-deta...63-5-ND/277209

    Z6 is a 74C04N, so I think this is the correct replacement: https://www.digikey.com/product-deta...66-5-ND/277212

    Do this appear to be correct parts?

    Thanks!

    -Kevin

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