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Discussion Starter · #1 ·
As some of you may know, I have a tired BG800 that I use for the kids, while I reserve the BG808s for my wife and me. The bg800 has about 50k hours on it and works great. Great exept for this. The 800 is now starting to do something VERY WEIRD. When a white background is up, the green gun surges in brightness and then goes dim, the other colors are surging as well, but not in sync with green. The screen goes greenish, purplish, greenisn, about every second or two. It is like I am cranking the G2 up and down. I have another bg800 that I sold to a friend that I can use for parts swapping/ troubleshooting, but I don't have a clue on where to begin......... The tubes are weak in this unit, so I have to drive it rather hard to use it with ambient light. The tubes are original, since all serial numbers match (both tubes and cards).




Any ideas? HVPS, SPLITTER, FOCUS BLOCK? I am lost.


Thanks,

Garrick
 

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Garrick,


If the picture size is expanding and contracting while focus is coming and going... pretty much for all tubes at the same time I would suspect the HV chain including the EHT, quadrupler, and splitter. It would do this as sceens change from dark to bright etc. However, your comment that they are not doing it together wouldn't seem to support that idea and you didn't mention any size changes.


What video input/mode are you using?


One time I saw something seemingly similar where I had color shift issues and it actually turned out to be my line doubler. Have you tried inputting video into different inputs and from a different source?


I'm not sure if the focus module could be the culprit, but things that come to mind for me are the input rgb board, quad decoder, and output amps.


What else could you tell us?


Mark
 

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Discussion Starter · #3 ·
It is independent of the source, and the size does not change. It really does not seem to go in and out of focus. The green does get a little blurry when it surges, but it get just as fuzzy when I run the contrast up. The surging is smooth, and convergence stays put. Should I try swapping the SMPS?


By the way, I am still driving those eeproms around in my car. They will have more miles on them with my commute than the projector does. :)


I just re-checked after about 4 hours of run time. It doesn't do it anymore, but the blue and green tube do something very similar when I pull up the white screen on nokia. I pull up a full white screen, and green and blue surge bright, and then go dimmer. If I pull up just one color, it is much worse, but red is solid. Green is the worst. It starts out very bright, goes too dim, and then ends up somewhere between the two.


By the way, this does not happen at low contrast (
 

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If it's all 3 tubes then it's probably not the neckboards.


Based all all the other info here, my guess is on the quad decoder board first, then the RBG input board. If all 3 tubes did the same thing at the same time then it could also be on other boards....


Kal
 

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Discussion Starter · #5 ·
So just start shotgunning things? I can certainly do that, It just seems that there is a current that is ok for inrush, but then some power source sort of craps out and sags badly. It then makes some sort of a comeback, but never the original brightness.


What regulates the brighness/contrast? Could I check that voltage and watch for fluctuations? I don't know too much about pinouts, but I have an oscilloscope and I'm not afraid to use it.


Thanks,

Garrick
 
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