CurtPalme.com Home Theater Forum

[RogerH]

Since new (350 chassis hours ago) my XG-852 has always had a green hump in the middle of a gray scale and a hint of red going to black. I have been searching the archives for my particular problem, but I'm afraid if an answer is out there, I'm missing it in the noise.

I have taken the projector through several slightly different G2 white balance procedures ( Guy Kuo's primarily) with some KennyG variations (using the recommended test patterns), and there is always a problem whenever I get to the part where I need to set BRIGHT GAIN to make a GREEN 50 IRE window barely black (with brightness at 0)

The RED and BLUE BRIGHT GAIN can make the inside of the 50 IRE window black with the window's edge enhancement still visible. But on both R and B there is plenty of margin to spare in the setting so I could conceivably make the whole thing black if I wanted. Typical BRIGHT GAIN settings have been coming out 33 RED and 45 BLUE for black inner window with border visible.

Why does the brightness of the window bottom out with G BRIGHT GAIN of 39, with the window brightness several steps above where it should be to match the R and B? Any setting below 39 does nothing to decrease the brightness of the GREEN window or its border.

There is not a lot of brightness with this setting, and if I squint it could still be considered "barely black", especially if I set the others to match. The point is that the R and B have more range to darken, and the G does not.

Other than that, the whole procedure is predictable and there is no problem obtaining testpoint voltages within the 2.5v spec, and with the AKB test switch turned on/off a grayscale looks almost identical. I am not finding any combination of DRIVE CONTROL and BRIGHT BIAS that will keep the 80/30 IRE levels looking gray without the green in the middle.

Can anyone steer me to the most likely place to look for this problem (if it is a problem)? I have scopes and other some other test equipment (and the service manual) but I don't want to go poking around looking at neck waveforms to confirm pot settings if the problem is elsewhere. There have never been any hardware adjustments (pots) while it has been in my hands, although I have scoped a few test points on various boards in the past to make sure things were in tolerance (it had a very rough ride in its orignal shipment).

So my questions are:

1) Green hump-is it related to my G cutoff problem, and where do I look?

2) What is the definition of"make raster barely light up" during the BLACK BIAS adjustment, when the faint raster is quite washed out by the glare of the log steps pattern? Even the BRIGHT BIAS setting to make the 2 IRE bars just disappear in the following step depends on whether I am looking with the glare of the display menu or if I turn it off immediately after the adjustment.

2.5v plus/minus 0.1 v I understand, but "barely visible" seems highly subjective to surrounding glare when looking in the lens. I'm not sure these thresholds are that critical, but I would like to hear how others interpret this.

[jarseneau]

1. Just a stab in the dark here but maybe your green tube is a different type than the RED/BLUE such as some are P16LJE08... and the other is an 07 or 06. There are neck board modifications to correct for this. A thread search for any of the 3 tube numbers should help explain what needs to be done.

2. When I look for the raster 'just lighting up' I focus on very edge of the image area painted by the scan lines. I then increase brightness until I see it just appear. Just be consistent from tube to tube as far as the spot on the face you are observing and the brightness.

[RogerH]

Actually both the red and green are JE07 and the blue is a JE06. I have this same combination in another 852 (my parts/experimentation projector) that was built about 18 months earlier, so this must have been common.

I'm hoping to get the simple direct answer on which voltages or waveforms to check, because I need to get a scope up on an 8' ladder to do anything. I'm curious about the cathode amplitude on the green tube, a service manual step that is skipped in the various white balance procedures out there. Something is off in the projector, even if its never been tweaked.

Your comments on raster are good, and inadvertently that's what I eventually did. It just seemed odd to me to be trying to sight a raster with all the glare. I ended up making the raster clearly visible, so I could see where I should look, then I backed off and just brought it up to where it was barely visible on each tube.

For the 50 IRE/0 Brightness part of the procedure, I would have to make each CRT window image fairly visible to keep them matched because of the green bottoming out. Maybe this is not an issue, because another procedure call for doing this part of the test with a 30 IRE, which I could probably easily make black on my green CRT.

The green is still a little hot in the middle of the grayscale when I get done, regardless of which procedure I follow. I can go into the user white balance controls and pull the white setting of the G tube down about 10 points and improve the mid, but the near black suffers. And I don't think that is the intent of the whole G2 cal anyway.

I appreciate your comments.