68kMLA Classic Interface

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12" RGB Display issues
Posted by: Westinghouse on 2016-08-03 18:32:35 Hi All, Apologies if this is in the wrong category. Received a 12" RGB Display today, and the picture geometry is distorted. I've attached two images - one was shot vertically, and one was shot horizontally. Basically: the picture balloons out wider in the middle, there's a bright horizontal line, and a band above the bright line is stretched vertically. Hoping to find out which component is faulty, and if a fix is viable?
Posted by: Byrd on 2016-08-04 03:28:33 It could just need adjustment of the dials - try to find the vertical and horizontal sync (often marked as vsync or hsync)
Posted by: bibilit on 2016-08-04 04:24:17 IIRC Techknight was dealing with a similar issue.
Posted by: Westinghouse on 2016-08-04 06:15:31 It could just need adjustment of the dials - try to find the vertical and horizontal sync (often marked as vsync or hsync) That's the first thing I tried. Adjustments in the back are: -Vertical Position -Horizontal Position -Vertical Size Vertical and Horizontal position adjustments move the picture as expected, but do not affect the distorted geometry. Vertical size adjustment will adjust the size of the picture, and also move the location of the horizontal line and the associated distortion. With the size adjusted to minimum, the horizontal line ends up at the top menu bar.
Posted by: Godzil on 2016-08-04 06:25:58 Considering the age of the screen, changing the electrolytic cap should help too.
Posted by: bibilit on 2016-08-04 07:56:10
Posted by: Westinghouse on 2016-08-04 10:36:44 Wow, bibilit -- that's definitely the same issue! I'll watch the follow-up repair video; thanks! edit the second video in the series does a great job of getting to the probable root of the problem, but no actual repair is completed to confirm, due to needing parts. I wonder if Techknight has gotten the parts and finished this project.
Posted by: techknight on 2016-08-04 16:24:25 I never uploaded the rest of the content. The internet connection here where I live is well... I think I could do better with dialup. Yes this monitor is fixed. It was a handful of leaking capacitors near the yoke plug, and near the front of the unit by the horizontal drive transistor. Right next to big VERY TOASTY resistors. Also, dont keep running it until you fix it! it will eventually and very quickly blow out the horizontal output transistor. The monitor will quickly shut off and start chirping loudly.
Posted by: Westinghouse on 2016-08-04 19:31:56 Glad to hear you got it back up and running, Techknight! After hearing how it went poof after you'd had it running, I resolved to not turn mine on again until I fixed it. Any chance you could indicate the affected capacitors on a photo, or on a screen grab from your video? Do you happen to remember the cap values? Thanks for your help - your videos are really informative.
Posted by: Godzil on 2016-08-05 01:34:19 Honestly if you are ready to change one cap, do it for all electrolytics, they all will fail as they are old, so instead of having to open and do the replacement in multiples operation, do it in one, thing would be better.
Posted by: Westinghouse on 2016-08-05 16:36:58 Well, there's a lot of cap goo in there. That was my first time taking an anode cap off. Phone went off just as I was doing it and nearly gave me a heart attack! Technight, did you end up replacing TA8403K and LA7824 like you mused about in your video, or was this purely a cap problem?
Posted by: Westinghouse on 2016-08-05 16:40:33 Underside of the board....
Posted by: Westinghouse on 2016-08-06 11:08:15 Success! The culprit in this case was likely C418, a 2200uf 6.3v cap which leaked all over the place. I also replaced: C512 - 100uf 50v C417 - 2200uf 35v C920 - 2200uf 35v C517 - 100uf 25v I actually replaced these and tested the monitor before I swapped out C418 - with no change. That is what leads me to suspect C418 as having been the problem the whole time. That, and the mess of fresh cap goo on the underside of it when I desoldered it. Thanks everyone for the advice and direction!
Posted by: techknight on 2016-08-07 13:30:26 Technight, did you end up replacing TA8403K and LA7824 like you mused about in your video, or was this purely a cap problem? Nope, I was rambling on in that video on what it could be if it wasnt caps.
Posted by: djhaloeight on 2016-08-15 21:10:36 IMO these are the best monitors for the pizza box Macs. They look so perfect sitting on LC's or equivalent Performa's. I scored mine on eBay for like $45 bucks. Its working perfectly, but I suppose I should do the caps sometime soon, just as preventive maintenance. Good job! 🙂
Posted by: bibilit on 2016-11-01 00:43:05 Hi, replaced exactly the same capacitor yesterday evening: /monthly_08_2016/post-2642-0-52677200-1470440152.jpg">View attachment 9675 The 6,3 V 2200 uF on the right with grey glue on it. was leaking. Screen has a perfect image and colours.
Posted by: techknight on 2016-11-01 10:34:30 I recommend upping the voltage rating, and going with a 105c cap. it sits right next to those 2 resistors which supply the drive current for the horizontal drive transformer and transistor, so they get HOT.
Posted by: bibilit on 2016-11-01 10:58:29 Yes used 10 volts IIRC, have not the lower one anyway.
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