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Thread: [FIXED!] MS8-26SU with dim/noisy image

  1. #1
    . furntree's Avatar
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    Thumbs up [FIXED!] MS8-26SU with dim/noisy image

    I have a MS8-26SU that I am a bit stumped on.

    After getting everything setup I'm getting an extremely dim image that has a lot of wavy noise in the background.

    As far as I know through testing my signal source is clean. The brightness pot needs to be at about 80/90% before a reasonably bright image appears and is pretty much blank in the lower 70%.

    I measure perfect B+ with 92V on the test points, I have a good syncing source, there are no obviously leaking capacitors, no excessive 15khz noise, and no obvious deflection or geometry issues, so I am unfortunately a bit stumped.

    There were a few bad/dry solder joints but nothing too crazy, and I didn't fix anything by re-flowing the bad joints. The chassis does have the classic Nanao heat damage near the center, but there doesn't appear to be any lifted pads and all large resistors seem to test OK! (I haven't measured all of the tiny ones)

    In the mean time I have some capacitors on the way and will do a little more digging into the neck board. I've read in another thread here that the electrolytic on the neck board can be the culprit for dark image, but I will believe it when I see it.

    If anyone has any ideas let me know! The convergence and geometry adjustments I can handle. I just hope I don't have a bum tube.
    Last edited by furntree; 11-20-2017 at 10:23 AM. Reason: fixed!

  2. #2
    Rasputin's Rose Gardener
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    Did you try adjusting the "screen" pot on the flyback?
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  3. #3
    . furntree's Avatar
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    Quote Originally Posted by daskrabs View Post
    Did you try adjusting the "screen" pot on the flyback?
    Yes, I have tried adjusting the screen voltage/B+ without much change and any large increase causes the expected retrace lines. I am thinking this is something a bit deeper down.

    Edit - I was able to mostly solve this brightness issue by replacing C332 on the neckboard per recommendation, finding a couple more questionable solder points, cleaning the RGB gain and bias pots, and adjusting accordingly. I still have some slight image noise and breathing effect so maybe a whole kit would help.
    Last edited by furntree; 11-14-2017 at 10:52 PM.

  4. #4
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    If you want more answers you could always post this on ArcadeOtaku. Grantspain over there should be able to say what might be causing it.


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  5. #5
    . furntree's Avatar
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    icon25.gif Repair log and update!

    After performing a bunch of maintenance on this I wanted to report my findings and what worked for me.

    Lot's of bad/dry/missing?? solder joints in places that are easy to skip over visually.

    The high temperature part in the center of the board is worse than it looks at first glance.

    Doing a cap kit really brought the geometry in pretty well without a lot of tweaking

    NARROW mode seems to be the way to go all of the time at least for me.

    C332 helped give subjectively more saturated color

    Nasty lifted solder pads @ C431, C432, and C433. I did a scrape and stick with some long legs and it seems to be holding well.

    R433 and 436 were measuring fine but I put in nice new ones anyway. (They get really hot)

    Need to fix the dynamic convergence in the bottom next chance I have time to mess around. Working great and looking great now! There were no major failures just needed some TLC.

    https://i.imgur.com/Djz16u7.jpg
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    Last edited by furntree; 11-20-2017 at 08:39 AM.

  6. #6
    Benimaru's Hairdresser
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    Looks a brilliant picture, well done. I have a MS8-26 in the shed that has flat lined, but it’s getting cold here!
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