CurtPalme.com Home Theater Forum

[deronmoped]

OK, I think I have a better understanding of what the problem is. What happens is the green is extra bright on start up and then after a couple of minutes it corrects itself. Now I can fix it right away if I turn the G2 down. So my though right now is whatever has to do with the G2 on the green is having problems.

So what do you guys think I should be checking? HV PWB, neck board...?

If it is the tube, can that be fixed or should I just use it as it is?

Deron.

[deronmoped]

I checked the neck board, that seems OK, not much to go wrong there.

I read a interesting description on how a CRT works, in there it says the contrast and brightness are controlled in the video preamplifier, is that true with our front projectors? I took a look and I could not find a preamplifier listed in the schematic, it looks like it is called the gain control. I will pull that card and check it out.

Deron.

[Mark_A_W]

Without a spare set of working boards to swap in and out, I don't know how you are going to fix this Deron

[deronmoped]

Mark, why would I need to use my spare boards? I do have a 9PG test mule and almost a complete set of extra boards. I have not tried swapping video boards as I'm under the impression that they have to be set up to work correctly. Anyways I would want to fix the problem board.

Deron.

[Mark_A_W]

Yeah, but which board? It might be the video board, it might be the gain board, etc.

Use your spare set to isolate the problem.

[deronmoped]

I checked out the gain and V4 boards and the caps tested good, actually real good, I noticed that the video boards caps seemed to be in worse shape, may replace a few more of those. A visual check of everything else looked fine.

So Mark are you saying it is OK to swap in the boards that need some sort of set up with a scope and that will not cause any damage?

Well anyways I might have found the problem, when I was adjusting the green G2 again as it was too bright I noticed that the "screen control unit's" pot or whatever it is, seems to be going bad. I could make the brightness jump around by rocking the knob. It seems like the contacts in there are going. I will swap the one I have off my 9PG, it's the same part number. I do have a extra besides that, but it's a different part number and has extra connections on it, so I may be looking for one.

Deron.

[deronmoped]

It was not the screen control. I then tried changing the gain board and it was not that, swapped out the video out board and that seems like it is the problem. It has started up correctly a couple of times now, going to keep my fingers crossed.

I went over this problem video board several times now, checking the ESR on the caps, testing diodes and resistors and giving it a good visual inspection, anyone know what else I can do? I hate to just save it for parts, would want to have it as a good running back up.

When I swapped in the video board, I though that all the colors and gray scale... would be way out of whack, but everything looks just like before, excellent. This board that is in the PJ now came out of my 9PG test mule, I guessing that these boards from the factory must be set up on a bench so they are pretty much all have the same settings. Anyone know if this is true?

Deron.

[Tinman]

Deron, check the 10uF 160v (I think) caps on the video out board. If nothing else, change them anyway.

Marc