CurtPalme.com Home Theater Forum

KrisRoberts · Joined: 21 Jan 2007 Posts: 115 Location: San Diego

The blue tube in my G90 has recently started flickering when it should be completely dark.

Its faint, but noticeable on dark scenes especially if there are letterbox areas above/below the main image.

It seemed like it started happening suddenly, but its been consistent since I noticed it (about two weeks now).

The tube has been in the projector the two years I've owned it, and has just about 2k hours on it.

On the unused/disconnected Input A and even with the service menu blue cut off, the blue tube shows a pattern with static and occasional flashes or bands of lighter areas.

The field on the blue is a trapezoid, it doesn't cover the entire face of the tube or run off the edge - does look like its constrained by the raster.

And if there is anything of much high contrast it doesn't seem to flicker. There is still more of a static background than there should be but at least it doesn't seem to fluctuate as it does when its trying to be all black.

Changing to the other inputs I use and with or without a signal doesn't make any difference.

Red and green are turning off completely like normal.

Adjusting Bias, Brightness, Contrast and Gain do not affect the problem (and work like they should).

I did open it up and pull and re-seat all the boards, but that didn't change anything.

I also did try swapping the neck board amp but the problem persisted.

Lens on, peer inside and compare with red and green. 4.3MB
G90_Blue_Flicker_01.avi

Lens on, peer inside turn contrast and brightness down. 3.2MB
G90_Blue_Flicker_02.avi

Lens off, power up turn contrast and brightness down. 5.1MB
G90_Blue_Flicker_03.avi

Lens off, turn bias down and up. 4.9MB
G90_Blue_Flicker_04.avi

Lens off, quick compare with red and green. 1.0MB
G90_Blue_Flicker_05.avi

Lens off, quick view. 1.6MB
G90_Blue_Flicker_06.avi

If they don't seem to just play for you by clicking the link, try right clicking and selecting the save-as option to download the file first.

So far the two things that have been suggested are either the neck board amp or the tube itself. Since swapping the neck board didn't change it, I'm wondering if there is anything else I can do to try and diagnose the problem. Sadly I don't have another blue tube to try swapping.

What do you guys think?

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

I'm assuming that when you swapped the neck boards you disconnected the wires, swapped the boards and reattached wires so the same feeds were still going to the blue tube. Are the wires long enough to leave them connected when you do the swap so that the entire feeds are swapped? There are so many possibilities involving various boards that the tube needs to be verified as to whether its the culprit or not. You could end up swapping stuff around for hours only to find its the tube. but if you verify its not the tube, then their are many options to try and narrow down which board has the problem.

KrisRoberts · Joined: 21 Jan 2007 Posts: 115 Location: San Diego

Thanks for the reply! Yes, when I swapped the neck boards I disconnected all the wires. And no, they are not long enough to cross over and connect to the adjacent tube. But it occurred to me to swap the red and blue tubes. Is there danger in that (beyond handling them, disconnecting and re-connecting everything)?

I know the focus and registration and everything would be way off, and I'd be careful not to display anything that went off the face (or even run it very long at all).

My thought was that if I swapped the tubes it would show whether the problem was in the electronics up the chain or in the tube itself. Are all the connectors that the coils and neck board connect to compatible between tubes?

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

KrisRoberts · Joined: 21 Jan 2007 Posts: 115 Location: San Diego

Okay thanks!

Yes, the problem goes along with the blue tube when swapped.

Harvey · Posted: Tue Apr 07, 2009 7:44 am Post subject:

There will be a micro schort in the Tube like part´s that comes in by a baad produktion... there is the only way to flash the tube with a tube refresher.. if you have luck it is like new after that..
I realy don´t know if anybody in this forum has such a refresching unit .. we in germany have some but i have not by such a expensive thing this time i thought about it but my wive find´s it not usefull for that little amount of dead tubes we have in my office..

CIR Engineering · Posted: Tue Apr 07, 2009 1:15 pm Post subject:

http://www.avsforum.com/avs-vb/showthread.php?t=1135866

KrisRoberts · Joined: 21 Jan 2007 Posts: 115 Location: San Diego

The sister thread over on AVS lead to the suggestion that its due to a contaminate in the projector. People reported seeing the same thing, and that when they tapped the tube they would actually see sparks inside. I never was able to see any sparks tapping it while it was on in the projector.

Taking it out, turning it up side down and gently/firmly tapping the bellows with a rubber mallet and then doing the same on the sides did improve it when I re-installed it. Its not perfect, but it is better. There still is a staticy field that is always illuminated, but it doesnt flicker and get brighter the way it used to. I still can detect it when the image fades to black, but its not as obvious as when it was changing intensity more.

My plan is to just live with it for a bit and see if it improves on its own - some people have suggested that the contaminant may just burn itself out or dislodge by itself. If its still an issue in a month or so I'll probably contact Charlie at VDC and see about sending the tube to him for eval/zap.

Thanks for your help guys!