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BG800 Intermittent Red CRT

371 Views 8 Replies 4 Participants Last post by  Maxxarcade
Being a relative CRT noob I couldn't have gotten nearly as far as I have without the guidance from reading these posts on a regular basis. I've had my BG800 for about a year, and up until now it has worked flawlessly.

When I crank it up to watch a movie (after ~30 mins warmup) it looks great. Then, maybe a half hour into the movie the red CRT will get dim, which obviously affects the pq. After around 5-10 minutes it brightens again and for the rest of the movie it's fine. No issues with green or blue.

I recently installed a hushbox following the excellent posts here. The temperature before and with the hushbox are consistent in the two places I measured (at the CRT neck and about 8 inches further back) so I don't think it's a temperature issue.

About the only thing I can think of is that when I was doing the setup on the ceiling about 2 months ago, I got confused between the rgb focus board and the rgb horizontal shift (deflection?) board. So I adjusted the shift rather than the focus. Once I realized this I moved the pots back to their original position and all seemed fine.

Any help would be greatly appreciated or let me know if I can make anything more clear.

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I would try swap red rgb-amp to green and see if problem move to green...
Thanks for the reply. Is that difficult to do? I have the service manual for the BG800 but it's a little difficult to follow. I was also thinking of electronically resetting everything to midpoint and just starting the setup over again.

I would bet you have a FET issue on the amp board or the G2 board is going bad.



For more info about the BG 800.

Thanks Pete

I looked through Curt's site on the BG800 but didn't see anything that addressed this issue. Good idea on the FET or G2 board. I'll do a search here and see if I can come up with something. I seem to remember a post here awhile back on how to troubleshoot/fix the FET on this machine. I'll post if I get it working so someone else that may have this problem can build on this.

Great website link Pete!

Beside the FET replacement procedure, he describes G2 adjustment (step 10), which was also a huge help for me. Sure enough, the G2 for all three crts was set too high. I readjusted them and did a top to bottom calibration (as well as "I" could anyway). After replacing the hushbox I watched ~2 hour movie and no problems with the crts. I'm going to keep my fingers crossed and if it can go a few more movies with no issues, then, hopefully it's problem solved.

I looked at the pictures on Lynxxx's web site and I didn't see that type of FET issue with mine. Could it have been that the red crt was just being overdriven?

In any case the picture looks better than ever. I let you folks know if this pops up again. Thanks again for the help!

I would recommend tha tyou replace the FET anyway. If they are not bad they will be. You will get a much better picture with new ones....

Yes definitely replace the FET's... I had the same problem with my BG800 last year and was able to lower the G2 and make it go away for a bit, but it will get worse and you will probably end up burning the tube. And the picture does improve noticably with new FET's on all 3 tubes. You will need to readjust the G2 afterwards, but there will be a lot more dynamic range/contrast with the tubes.
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