I have a odd problem with a Marquee 9500LC

It has a strange noise in the picture. Its always present. Even with the input disconnected and with test patterns up.

The noise is effected by the brightness and G2 controls. The noise also is picture related in that the noise changes depending on picture content. If I bring up brightness or G2 the noise becomes very easy to see.

It always appears as longish dots which are mostly diagonal and NOT locked sync wise and float around on top of the picture. Again its not locked to the sync.

Its really obvious in dark scenes.

The noise is in all three colors.

Any suggestions on where to look for the problem would be good. I have swapped the input board and the problem persisted.

http://www.xymox1.com/Work/temp/noise1.jpg

http://www.xymox1.com/Work/temp/noise2.jpg

I would start with the control module (CLM) , it's right next to video input. Usually caused by oxidation on the DPB daughter-board pins or socketed chip U7.

Interesting.... I will try that....

Any other thoughts ?

I suppose the only other things that might be involved are the neck boards ? and the HV module as it supplies G2 ?.

Interesting, I had not considered the DPB... Good thought...

On the neck card, near the video input connector are two jumper wires. Sometimes they get pressed down against the circuit bd. Pull them up as far as posible away from the PCB. Should minimize the problem.

Scott

Another good sugestion !... I will check all of these....

Hello

I have seen this when a projector has no neckboard covers. Also, you should have braided ground straps from the neckboard covers to the rear heatsink.


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Hello

I have seen this when a projector has no neckboard covers. Also, you should have braided ground straps from the neckboard covers to the rear heatsink.


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You raise a good point Tim, should there be three ground straps (one for each neckboard cover) and is there any other places that use (or could use) ground straps (I seem to recall MP talking about additional grounding but enigmatic as usual he didn't say where)?

Paul

When testing my work on the boards i run it with out those ground straps while testing, it usually does not cause what is posted above, but I may be a lucky one, But the two aquadag ground cables from the Bell of the tube tot he VNB are needed or you get arcs snapping all over. I think it might be something in the CLM/DPB or on the Vim, or the source itself. What are you feeding the PJ with?What's your video chain and is it in the image from all sources and also how does the Internal patterns look.

Athanasios