CurtPalme.com Home Theater Forum

[Curt Palme]

This happened to me today. Spent 5 hours chasing an obscure fault.

I had a Barco 708 that showed massive H interference lines on all tubes, all sources, and on the menus and test patterns. The only time you didn't see the interference was during warmup, when the video was muted, but you could see the raster. Oh, to add to the fun, the AKB level was all over the map, each tube would go bright and dim whenever it felt like it.

For those of you that know the Barco 70X series, the video signal route is pretty easy... video input board connects right to the CRT socket/video output amp.

I scoped each video signal as it went to the neck board, and saw the interference on top of hte video signal. Changed the video input board.... same problem.

Now, I've seen this problem in another 708 chassis. Changed every board in the set, HV section, etc, it's still sitting in the corner, patiently waiting for me to get back to it.

So I start scoping the power supply. I see that one of the power supply rails has some high frequency noise in it, over top of what's supposed to be a clean DC signal. I realize that I can disconnect numerous boards that this supply goes to while still being able to power the set on. I find that the HF noise goes away when I disconnect the RGB input board. I change the RGB input board again with a third one...same problem. Now I'm pissed.

I change all sorts of capacitors in the power supply. THey were slightly off spec with my Sencore capacitor meter, but nada, still the same problem. Convinced that the problem is on the RGB board, I start checking parts. Sure enough, the same part was bad on each damn RGB input board. Changed the part, all three boards work. I suspect that I have more RGB Input boards that have this part bad on them. It could be coincidence, but both chassis were actually low hour Runco 947s.

Sorry, I won't post more, I don't give away exact component repairs as most of you know, but once I checked the schematic, I knew exactly why the problem occurred. To make things worse, the part showed no external signs of failure.

What a waste of a day, my blood pressure was way up, but I live for this chit!

[Curt Palme]

This happened to me today. Spent 5 hours chasing an obscure fault.

I had a Barco 708 that showed massive H interference lines on all tubes, all sources, and on the menus and test patterns. The only time you didn't see the interference was during warmup, when the video was muted, but you could see the raster. Oh, to add to the fun, the AKB level was all over the map, each tube would go bright and dim whenever it felt like it.

For those of you that know the Barco 70X series, the video signal route is pretty easy... video input board connects right to the CRT socket/video output amp.

I scoped each video signal as it went to the neck board, and saw the interference on top of hte video signal. Changed the video input board.... same problem.

Now, I've seen this problem in another 708 chassis. Changed every board in the set, HV section, etc, it's still sitting in the corner, patiently waiting for me to get back to it.

So I start scoping the power supply. I see that one of the power supply rails has some high frequency noise in it, over top of what's supposed to be a clean DC signal. I realize that I can disconnect numerous boards that this supply goes to while still being able to power the set on. I find that the HF noise goes away when I disconnect the RGB input board. I change the RGB input board again with a third one...same problem. Now I'm pissed.

I change all sorts of capacitors in the power supply. THey were slightly off spec with my Sencore capacitor meter, but nada, still the same problem. Convinced that the problem is on the RGB board, I start checking parts. Sure enough, the same part was bad on each damn RGB input board. Changed the part, all three boards work. I suspect that I have more RGB Input boards that have this part bad on them. It could be coincidence, but both chassis were actually low hour Runco 947s.

Sorry, I won't post more, I don't give away exact component repairs as most of you know, but once I checked the schematic, I knew exactly why the problem occurred. To make things worse, the part showed no external signs of failure.

What a waste of a day, my blood pressure was way up, but I live for this chit!

[WTS]

One to put in the memory banks.

[stefuel]

Sounds like a conspiracy to me. I had a theory but a group of strippers somehow made me forget my theory.
Just another conspiracy. Do you know what's wrong with this country??? To many Goddamn conspiracies.
Now where did those strippers go