68kMLA Classic Interface

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Mac Color Classic screen issue
Posted by: GibLP on 2023-05-17 20:19:08 Hi All - I've purchased a Color Classic with a known display issue to fix. Anyone have any idea where I should start? From the reading I've been doing it would appear to be a degaussing circuit issue? Thanks in advance!
Posted by: Nixontheknight on 2023-05-18 08:10:59 Hi All - I've purchased a Color Classic with a known display issue to fix. Anyone have any idea where I should start? From the reading I've been doing it would appear to be a degaussing circuit issue? Thanks in advance! View attachment 56663 I recommend getting a degaussing coil to try and fix this
Posted by: GibLP on 2023-05-18 10:08:25 I recommend getting a degaussing coil to try and fix this Thanks! Will give that a try
Posted by: 3lectr1cPPC on 2023-05-18 10:49:56 Wow! That fault almost looks artistic. Good luck fixing it!
Posted by: ymk on 2023-05-18 11:23:32 It looks like the deflection yoke assembly may have rotated around the tube. Is it loose?
Posted by: GibLP on 2023-05-18 12:34:28 It looks like the deflection yoke assembly may have rotated around the tube. Is it loose? Thanks. Still waiting to have the unit in front of me, but you think based upon how much the picture is skewed, the Vertical Angle (PR) adjustment won't help?
Posted by: ymk on 2023-05-18 12:55:00 No, the screen will maintain a parallelogram shape if only PR is out of adjustment. The color distortion seems like the guns aren't landing where they're supposed to. That has me thinking either deflection yoke, convergence or worse, the aperture grill is misaligned after an impact.
Posted by: GibLP on 2023-05-18 12:58:03 No, the screen will maintain a parallelogram shape if only PR is out of adjustment. The color distortion seems like the guns aren't landing where they're supposed to. That has me thinking either deflection yoke or worse, the aperture grill is misaligned after an impact. Ahhh, gotcha... What have I gotten myself into? ha. When I saw the picture I had assume the color distortion was due to magnetic issue which could be solved with a degaussing wand/tool. Hopefully when I open it up I can see if anything looks out of alignment. Thanks
Posted by: ymk on 2023-05-18 13:06:03 When I saw the picture I had assume the color distortion was due to magnetic issue which could be solved with a degaussing wand/tool. The CC has a built in degauss coil. Try to get the geometry right first. If any color issues persist, it could be convergence. Look for any magnets in the case that might have been knocked off the CRT.
Posted by: Byrd on 2023-05-19 18:00:18 That looks like a knock/drop to me, the convergence rings have moved. You might be lucky and see where the rings have moved, often covered in glue or paint as way of marking the alignment.
Posted by: GibLP on 2023-05-22 07:17:25 The CC has a built in degauss coil. Try to get the geometry right first. If any color issues persist, it could be convergence. Look for any magnets in the case that might have been knocked off the CRT. That looks like a knock/drop to me, the convergence rings have moved. You might be lucky and see where the rings have moved, often covered in glue or paint as way of marking the alignment. Thank you All! Once I crack it open I'll see what we're dealt with and report back with some pics.
Posted by: GibLP on 2023-05-28 16:24:51 Hi All, I’ve been able to open it up and have a little improvement in the picture. I don’t see anything obvious on the inside that is broken or missing. The tilt was corrected easily with a twist of the yoke. I’m having trouble with the color correction however. If I adjust the ring for red, green is out of whack. If I adjust the green, red appears. Any hints on how to get this right?
Posted by: Nixontheknight on 2023-05-28 17:15:48 Hi All, I’ve been able to open it up and have a little improvement in the picture. I don’t see anything obvious on the inside that is broken or missing. The tilt was corrected easily with a twist of the yoke. I’m having trouble with the color correction however. If I adjust the ring for red, green is out of whack. If I adjust the green, red appears. Any hints on how to get this right? that seems like a degaussing problem, if you don't hear a hum on startup before the chime, try buying a degaussing wand or degaussing coil, otherwise, try placing magnets on the CRT (on the inside, not on the viewing area) and repositioning them until you get a uniform image
Posted by: GibLP on 2023-05-28 17:49:21 that seems like a degaussing problem, if you don't hear a hum on startup before the chime, try buying a degaussing wand or degaussing coil, otherwise, try placing magnets on the CRT (on the inside, not on the viewing area) and repositioning them until you get a uniform image Thanks. I hear the hum when turning the unit on so I assume the degaussing circuit is working. I bought a degaussing wand but it seems to have minimal effect aside from improving the initial “rainbow” picture to the one side green one.
Posted by: Nixontheknight on 2023-05-28 18:12:18 Thanks. I hear the hum when turning the unit on so I assume the degaussing circuit is working. I bought a degaussing wand but it seems to have minimal effect aside from improving the initial “rainbow” picture to the one side green one. then try getting some small magnets and taping them to the back of the screen and making adjustments until it looks perfect or near perfect
Posted by: GibLP on 2023-05-28 19:05:46 then try getting some small magnets and taping them to the back of the screen and making adjustments until it looks perfect or near perfect Thanks! I’ll give that a shot. Any idea what these horizontal lines every ~ inch are?
Posted by: 3lectr1cPPC on 2023-05-28 19:10:10 That’s the visible rastor of the tube. Likely means there’s some calibration issue. That and the other shape distortion visible signals to me that the analog board needs new caps and some adjusting, hardly unexpected. Don’t think that’s related to the rainbow-ness of the tube but that sort of issue is a bit out of my ballpark. Anyone know the best forum/place to go for CRT repair help? Seems they’d be able to help better than us here, even if most of us know at least a bit about how these things work.
Posted by: chiptripper on 2023-05-28 22:20:11 You can just leave the power on (but not booted) for a few hours and let the degaussing coil do its thing. If you hear it when you hit the back power switch, it should be working. I'm not convinced this is degauss related though. Sadly, this looks like aperture grill trauma. Hope I'm wrong. There should be a thin line running horizontally across the bottom third of the screen. That's literally a wire holding the grill in place, it's a Trinitron thing. If you can't see that wire... sadness. I'm by no means an expert, but this CRT resource has a blurb on aperture grill damage.
Posted by: Byrd on 2023-05-28 23:11:31 I'd still put it down to a drop/knock, as chiptripper noted damaging the aperture grill sounds plausible. That's not a normal degaussing pattern. If you Google "trinitron aperture grill damage", you get things like this which suggest a replacement tube. https://www.reddit.com/r/crtgaming/comments/tnpey4
Posted by: GibLP on 2023-05-29 08:07:25 Thanks All… at this point I may just cut my losses and dump it as I’m not seeing that characteristic trinitron line. 😞
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