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Model 4P Video board capacitor replacement

arnuphis

Member
Joined
Sep 1, 2020
Messages
45
Hello everyone! So it's time to take a look at my Model 4p. It has a new PSU and works great but the picture shrinks and expands at random. So I am thinking its time to replace the caps in the video board. I checked the service manual but it lists dozens of them. Does anyone have recommendations as to which ones they would change? Also seeking a good parts list for Mouser or similar?

As always, thanks in advance!
 
Just out of interest, is the picture shrinking and expanding truly random, or does it actually depend on the picture content (e.g. overall brightness)?

This might narrow down the problem area.

Dave
 
Hey there. Its at random. Not just when drives are accessed or brightness adjusted. Machine can sit there idle and it will just do it even if I lower the display to barely visible.
 
It has a brand new PSU. Rock Solid. This was the first thing I replaced when the issue started.
 
Hello everyone! So it's time to take a look at my Model 4p. It has a new PSU and works great but the picture shrinks and expands at random. So I am thinking its time to replace the caps in the video board. I checked the service manual but it lists dozens of them. Does anyone have recommendations as to which ones they would change? Also seeking a good parts list for Mouser or similar?
Does the picture shrink and expand just vertically? Horizontally? Both? Is brightness impacted when this occurs? Are there changes in the high pitched noises the CRT gives off? Does the issue start immediately after the machine is idle, gets worse or better when warm? Etc. Etc. If there are dips / brownouts in the 12V supplied to the board, both axes would be impacted equally. Note the "to the board" so you need to measure the voltage delivered to components on the board - there may be a wonky connector that is limiting current or a bad solder joint.

-- Bob
 
As I recall its vertical only. No changes in brightness or 'whine' from the flyback. Its within a short time of powering up and just does it and random intervals. I can capture a video and link to it when I get a chance.
 
I tried to film it but its well nigh impossible to capture 'expand and shrink' effect. Also it seemed to know when I was filming and would do it after I stopped haha. Going to open her up this weekend and check joints etc.
 
Do the obvious things first: bad solder joints, solder splashes, flux, bad connector connections.

Dave
 
It's all fixed. Reflowed solder on the board which plugs into the crt yoke. Cleaned up contacts on video board connector plug. Inspected all the caps and they look good. Picture is now rock solid.
 
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