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Discussion Starter · #1 ·
Hi !


I searched alot culdnt find answer in forum.


I have a B 800 G.


Working great until 2 weeks ago.


Now when i turn it off, a bright dot comes in the middle of the screen quite large.


Happen when going to standby mode.


Only problem i can se. (working great when running) .


Tried to adjust the power to 17.2 v as seen on Curt P , web site.


Not helping .


Buy the way anyone have some fet to sell to the amplifier bords ? mayby its time to replace them.



Thanks.


Best regars Stargatefour
 

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THat is what you need, the video output boards. You might also need a power supply repair. THe 17 volts should be set to 17, not to 17.2.


I don't have spare FET's, but I do have hte boards. THe FET"s are getting really hard to find now.
 

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Quote:
Originally Posted by Curt Palme
THat is what you need, the video output boards. You might also need a power supply repair. THe 17 volts should be set to 17, not to 17.2
This was something I added to the text on your site Curt:

"(Note from webmaster: If your projector starts to display a dot in the middle of the screen during shutdown, one culprit can be this +17.0VDC source which has drifted slightly below +17 volts. I recommend adjusting it to +17.2VDC as it can drift down slightly over time as the capacitors age)."


From my experience and what I've read here from others, I'm not the only one recommending that the voltage be set just slight higher then 17.0 to compensate for sagging caps. Adjusting it to exactly 17.0 is probably better, but I'm noticed that the large center spots during shutdown start to appear as soon as the voltage starts to sag slightly (even 16.95).


Anyone else?


If you still see the big dots during shutdown, the something else is not right. Most likely the RGB output FETs.


Kal
 

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I agree. I've played extensively with that pot, and if you get spot burn or a sign of a spot at turnoff, then you have other problems. Bumping the voltage up is only delaying the inevitable spot burn.
 

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Discussion Starter · #5 ·
Quote:
Originally Posted by Curt Palme
I agree. I've played extensively with that pot, and if you get spot burn or a sign of a spot at turnoff, then you have other problems. Bumping the voltage up is only delaying the inevitable spot burn.


Ohhh.. scaring me now..


Have tried between 17-18v no difference.


Since i have mint tubes in my barco id like them to stay that way. .


althought i have noticed that the plate behind some of the amplifier rgb bords get realy hot, dont know if its normal. (can hold hand there but..)


noticed to that a black picture and a red figure are present the black tend to be little red, very hard to se but its noticable if you know about it.


I have to buy some fets and change them before powering up again ..


Whats the value on new FET ? must be measureable ??


And thanks to all nice answers.

Best regards STG4
 

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Yes, you need FET's. I never measure them, I automatically replace them when I get sets in for resale.


Curt
 

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Discussion Starter · #8 ·
Quote:
Originally Posted by kal
See this page:



If you've started developing it on all 3 tubes at the same time then it's not the FET's. The odds of all 3 starting to go at the same is almost zero.


If it's only the red tube, try swapping a the red RGB output module with the green and see if the problem moves over.


Kal
Ok.. i think at least there is on 2 tubes..


I have ordered some FET now . Better change them anyway.


Is it realy safe to test again ?? i dont like to ruin my tubes. ..


althought i have a green and a red spare with uneven wear on , but the blue is the one that is in projector (perfect condition)..


Is it ok to only run 1 tube (red) and then shift the amplifier boards to see if its on all tree ? .


(disconnect the ampliferboard from tube ?? safe )


Sugestion please how to best narrow down this fault .


Thanks for support
 

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stargatefour:


Give me a call and I'll try and sort this matter out with you.


/CJ
 

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Discussion Starter · #10 ·
Found this from a good source.


"Spot suppression on the BG/BD 800 was always an issue. I'll dig out the circuit diagram and have look. If I recall there are a couple of capacitors which are designed to kill the beam the moment the PJ goes off. If these go bad then tube burn can result.


I'm not aware that incorrect g2 voltage will cause spot burn but it was common for the hire industry to turn then up to get moprte brightness.


Always put the old 800 series into standby with remote before the mains switch."


Witch capacitors !!!


I have them all available . but need to know whitch to change . (havent answer my mail yet)


Curt you know this ??


pleeeeese help .
 
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