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Thread: Commodore 1084D Monitor needs percussive maintenance - Where to look?

  1. #1
    Join Date
    May 2011
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    Default Commodore 1084D Monitor needs percussive maintenance - Where to look?

    My ever troublesome 1084D monitor is at it again. Or, perhaps more accurately, has just never stopped being at it.

    A while back I had to hotwire around the power switch in this monitor because it had failed, which is apparently a common problem. However, since then I've still been having issues with the monitor powering up. (I did test the switch and verify it was bad, which makes it all the more interesting that it's apparently failed in multiple places at once.) The monitor is now behaving like it has a loose connection somewhere; it generally works fine once it's running, but particularly when first powered on (or after moving it) it sometimes won't come on, sometimes producing a gentle "tic" sort of sound like power was briefly applied and then pulled. (Or it could be the sound of something briefly arcing.) Slapping it a couple times will generally get it going.

    At first I thought I had a bad splice in the wires where the switch was, but I've redone that and that's definitely not the issue now. This weekend I had it opened up again to touch up the splice, and while I was at it I freed up the board just north of the power socket that has the small (isolation?) transformer and fuse on it and reflowed the solder connections on that, since they did look mildly sketchy. I thought that'd fixed it, since it behaved perfectly after that for several cycles... but now it's at it again. I assume at this point the problem must be somewhere on the large circuit board under the tube, which I'm totally not thrilled about pulling out to work on, but I guess that's how it goes.

    Is there some place in particular on these monitors that's prone to causing this sort of behavior? Is it likely in the area of the flyback transformer, or could it literally be anywhere? When it flakes out it seems like power it going out entirely in the monitor, IE, the power LED and speaker seem to turn off as well as the tube.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  2. #2

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    For ticking I would look for solder ring cracks in the power supply area around the transformer T121 and the IC on the heatsink I101. Put it on it's face and slide the board up to view

    1084d ps cracks.JPG

    Larry G

  3. #3
    Join Date
    Jun 2012
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    Also just wondering if you have any dust or debris on the spark gaps (if it has any)...

    An 'old fashioned trick' was to run the monitor in the dark and visually look for signs of arcing - keeping your body well away from any contact with the monitor itself !

    Dave

  4. #4
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    It really just feels like a loose wire/joint, it's not "cracking" like I've heard from monitors where the flyback insulation is breaking down, but man, it's been driving me crazy trying to find it.

    So the main circuit board just slides out once you have the back out? I wasn't quite sure how it was anchored in there. I was really hoping I'd be able to find the issue without having to detach it from the tube, totally not looking forward to that prospect.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  5. #5

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    The original-form-factor macs get exactly what you describe on their analog boards. In that case it is a solder issue and renewing the solder between the components and the analog board, resolves the problem. I'm getting prepared to redo my 1084D - I sourced a 'new' switch from a dead Mac monitor that used the same switch mechanism and I've gotten new caps put together, but there are a couple of projects ahead of it right now.

    I wish I could point you to the right spot to look, but I'm about 80% certain the solder joint (somewhere) is your problem - if it goes on long enough there will be discoloration on the circuit board.

  6. #6

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    Dry solder joints on the flyback transformer are a common problem with the 1084 range. Mine used to start losing the picture as it warmed up, but a good slap on the side of the case would fix it for a while. Re-flowing the flyback fixed it.

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