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Thread: Tandy CM-2

  1. #11
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    Damn. I was right.

    20181110_112351.jpg

    Hard to see in the pic, but it's bad. If you're looking at the pic it's close to the back. Broken right apart on the left but a long hairline crack runs off from it. Probably not repairable.

    If I wasn't so afraid of the CRT and flyback, I'd remove the board and see if I could repair it. But I think it's probably beyond that. Might just have to recycle the monitor, which is unfortunate, given CM-2s aren't that common.

    Most likely somewhere in transit it got jostled hard, and the aged PCB inside flexed and broke. What a disappointment. You just can't have nice things with post/courier people.

  2. #12
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    Yeah I see what happened now. There is a channel on both sides of the case that the monitor PCB fits into. It appears some force popped it up and over the channel on the left side.. twisting and breaking it. Apart from where the board actually broke a hairline crack extends across many traces about halfway across the PCB. I think this is unrecoverable. Going to recycle it.

  3. #13
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    I've had a more detailed look at the board. I'm still afraid to try pulling it out all the way, but I did manage to pull it a bit back to inspect the damage. I'm not going for complete removal as that involves disconnecting the CRT anode and I am not confident in my skills at discharging that, and as they say, literally, once bitten, twice shy.

    It appears I have some fortune in that the monitor PCB appears to be single sided. So I think it might be just a matter of epoxying the big 'bite' together, drilling a small hole at the end of the crack to stop it from progressing, and then soldering jumpers wherever traces are broken. I think. I'm just a bit shy about disconnecting that anode, and of course the damage is out of reach because to get at it you gotta slide the board back out of the front of the case.

  4. #14
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    Re. the anode it's nothing to be scared of. With a CRT this old any charge in it will dissipate out over a few hours. I made a video about how I replace the Model III/4 CRT and I just let it sit overnight and every time I take the anode off there is no hint of a spark. It would be different with a brand new tube and flyback but with old ones its pretty safe to just wait overnight or if you are especially cautious a couple of days and disconnect it.

    As for the board, I have done what you describe a few times now and as long as you can connect the broken tracks (use wire, or leads cut from a resistor not just blobs of solder) you should be back in business. Then mark if you wish to sell its in the future it's not to be shipped - pickup only, because while the repair works it won't stand up to much abuse in shipping.

    Hope this helps,

    Ian.
    *There is never a charge for Tech Support even if you don't purchase from me - We are Enthusiasts Helping Other Enthusiast and that is just the way it is

  5. #15
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    Quote Originally Posted by TRS-Ian View Post
    Re. the anode it's nothing to be scared of. With a CRT this old any charge in it will dissipate out over a few hours. I made a video about how I replace the Model III/4 CRT and I just let it sit overnight and every time I take the anode off there is no hint of a spark. It would be different with a brand new tube and flyback but with old ones its pretty safe to just wait overnight or if you are especially cautious a couple of days and disconnect it.

    As for the board, I have done what you describe a few times now and as long as you can connect the broken tracks (use wire, or leads cut from a resistor not just blobs of solder) you should be back in business. Then mark if you wish to sell its in the future it's not to be shipped - pickup only, because while the repair works it won't stand up to much abuse in shipping.

    Hope this helps,

    Ian.
    Thanks Ian. I've heard that I should be safe.. monitor has been unplugged for a couple days now. It's the fact that you cannot see a charge that makes someone like me have trouble believing it isn't there.

    I'm surprised that whatever happened to it was sufficient to bounce and twist the pcb out of its track but did not damage the case.

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