Help with Sony PVM Monitor losing color?

[rodcastler]

Hi, I am trying to fix this Color monitor.

1) It works well, with a crisp and colorful image…  sometimes.
2) Most of the time it behaves with a failure mode where it displays only b/w, with some flickering near the bottom section of the screen.
3) Under this failure mode, when fed with B/W, the image looks as expected (shown in the first picture with grayscale gradient bands)
4) But when color images are fed, it shows them in B/W. The second photo shows the display when horizontal rainbow colors are fed through composite input (vertical B/W thin lines are displayed instead).

Sometimes it comes back to normal, without user action involved. I don't believe it's temperature related because It may randomly go back to normal without touching anything.

I believe these monitors can automatically detect NTSC/PAL/SECAM. I suspect it is switching to PAL for some reason but I am not sure.

Any ideas of what could be failing?

[m k]

4) 2nd picture is not color image in B/W, put there some real stuff.

Seems that color burst has something to do with it.

[rodcastler]

4) 2nd picture is not color image in B/W, put there some real stuff.

Correct. Some images get distorted: That one is what shows when a horizontal bar color rainbow is fed in.

Here are more examples.
The sky behind the mountains as well as the background behind the "level 04" text, should be solid colors, but vertical banding occurs.
The complete images shown should be full color.

[jeremybh1]

Are you aware of the big service bulletin Sony had on the 9" monitors (in particular) about them loosing colour?  It's directly attribute to variable capacitors - they look like metal rectangles with a spot for a small flathead screwdriver to tune the capacitance.  These failed big time in the field and were replaced by Sony. 

[m k]

My guess is that colorburst is not found or PLL is not locked.

But it doesn't explain 2nd picture in 1st post.
If only colors are missing both pictures should be the same.

How the signal is fed in, as composite video or something else?

[rodcastler]

It’s composite what I’m using.

It’s not just color what’s being lost. Just like m k pointed out above, the second picture in the 1st post should show horizontal greyscale horizontal bands, something very similar to the first picture, but instead, thin vertical lines are displayed.

I’ll follow the service manual and will check the scope readings to see if I find anything.

[rodcastler]

Are you aware of the big service bulletin Sony had on the 9" monitors (in particular) about them loosing colour?  It's directly attribute to variable capacitors.

I was not aware of that, thank you.
Sure enough, it was the fault source. There’s even a pretty good youtube video that covers these variable caps, its consequences and how to replace them.