Abused Sony GDM-FW900 - AVS Forum
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post #1 of 6 Old 01-15-2012, 12:47 PM - Thread Starter
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Okay, I have come into a Sony GDM-FW900 that I believe has been put through a wringer. The case is not in the greatest shape, although I do not think that it has been dropped. I have yet to open it up.

What I am wondering about though, is if there are any symptoms that I might see for a tube that is dying or just been put through hell. I have only fiddled with it for about half an hour with a Macintosh laptop so far, haven't been able to really put it through the paces that I would like yet. But from the first power-up it seemed that the image was EXTREMELY bright. I went through the Mac's colour calibration procedure and on the very first test image, it just wasn't happening.

The calibrator instructed me to turn contrast to 100%, then adjust the brightness until a grey oval in the centre of an image appeared to be very faint. Additionally, the left and right half of the image which the oval is superimposed on, should be just about dark and the same shade. No matter what, I could still see the oval in the centre in its shade of grey, and the two halves of the pattern on either side of the oval were very distinct, all three areas of the image as distinct and as bright as day. This continues with contrast at 100%, and Brightness? At zero.

I went through the rest of the calibrator and got it to some kind of semblance of niceness but the image still appears very, very washed out for a CRT of any kind. Is it possible that there is an electronic fix for this in any way, like an overripe capacitor or something? The glass is in very good shape and there are no obvious deformities that adjustments can't take care of (geometry, etc.) but I can't see myself making much use of this with the brightness as it is. Should I work this over with some different sources and calibrations before I decide what to do with it? Is there any possible technical fix?

Edit: well I played with it a little more with my XBox 360, and the same deal. Just an overbright, washed out image in general. It is very sharp, and very smooth in that Trinitron fashion, but my Viewsonic P225f has a much nicer image. Blacks are actually black, and they are just slightly grey here, not a terrible image but if I could settle for this look I would just go back to an LCD.
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post #2 of 6 Old 01-16-2012, 10:47 AM
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The G2 voltage may be too high. I recall the same thing happening to a Dell UltraScan P991 (Trinitron tube) that I once had (I was not the original owner). You could try opening it up and turning down the G2 voltage (SCREEN) to lower the master brightness; usually controlled by a potentiometer on the flyback transformer.
Try fiddling with the Image Restoration option on the OSD menu first to see if that helps.
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post #3 of 6 Old 01-16-2012, 12:22 PM - Thread Starter
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I searched for info on this and it seems that some folks actually covered it in the unofficial GDM-FW900 thread, among other places. Looks like people are using a serial cable to make modifications to the firmware and correct this G2 voltage problem. Sounds like it could be dicey but I'm willing to give it a go.
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post #4 of 6 Old 01-16-2012, 12:53 PM
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G2 voltage is controlled by the flyback... use the manual asjustment its so easy... dont mess with firmware cause its pretty sure to fail.

The G2 adjustment is always situated on the flyback below the focus adjustment or on the board on the neck of the CRT.


Heres a pic and the lower one is the SCREEN/G2 adjustment.

Never mess around with firmware..

You adjust screen calibration by lowering your brightness to half. then lower the G2 until the black is black. After that you can make minor adjustments with the brightness control.
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post #5 of 6 Old 01-16-2012, 02:22 PM - Thread Starter
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I take it that is a "G2" that I see next to the screw in the centre? I'm actually a little less squeamish about trying the firmware calibration route, because I'm sure that this bit has not been adjusted, not trying to be difficult but I guess I just wonder why this physical adjustment would cure the problem if it weren't moved physically to begin with?

I have the service manual somewhere. I guess I'll take the cover off tonight and see what I can see.

Edit: Okay, if this is correct, it looks like Sony made these CRTs a little too "smart."
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post #6 of 6 Old 01-16-2012, 10:02 PM
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No... the bottom screw IS the G2 adjustment. Its labelled SCREEN. Its separate from the two focus adjustments on top. It can be turned manually with your hands or with a philips screwdriver. Be careful not to touch the focus adjustments... itll mess up precision badly.
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