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

furntree

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Hello KLOV Family!

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 on NG forums 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.
 

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Check Q570, Q571, Q572, and D574, all located behind the Brightness ADJ pot, beside the Width Coil. Try your cap on the Neck Board, but don't hold your breath :)

Also, for good measure. Locate R570 next to the flyback. Follow this trace from pin #10 of the flyback, two separate directions. Checking for continuity and bad solder/lifted pads. FBT pin #10 > R570 > D570 > C570 > to pin #1 on connector CN570. Other direction from FBT pin #10 > R570 > C579 > Check D576 just in case > D572 > R576 > R585 > Q571 > Q570 > Q572 > VR570(Brightness pot) > D574 > potentially something on IC101 may be the culprit, solder, ect....
 
Thanks for the info!

I actually went a little more low tech and spray cleaned through the gain/bias pots a little bit, along with a couple bad dry solder points on the neck board. It actually made a surprising difference...

I am still getting slightly heavy breathing effect with brightness change and a little shimmering noise. I saw your recommendation mentioned in the service manual as well for ABL and brightness issues, so it's probably worth checking. I'm not going to rule out the noise as my fault yet but we will see.

Thank you for all the information you have published as well, it makes this thing much easier to work on.
 
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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.

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.
 

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Awesome!! It's always great to see happy results, when working with these. I think I can speak for most, by saying Thank You for the follow up and information you provided :)

Nasty pads is about right, these chassis are the worst I have ran into, that have these issues. Even with the K7000's I've come across, nothing as bad as the lifting on these boards.


Side note: Maybe this weekend, I can get back to my old thread, and try to get the pics reposted. I know that would make Ken happy, lol.
 
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