Serious Val Problem with Panasonic TH-42PX75U plasma
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Drat! Can’t edit the TITLE!!! Obviously I meant “Serious Cal Problem…” LOL!
This model is similar to TH-xxPX65U, TH-xxPX75U, and TH-xxPX750U
This plasma is about a year old. Closer to the bottom of Panasonic’s plasma line that the top. No Gamma controls for one thing. Blacks jump up in level significantly if you exceed 29 fL for a 100% white window and go back to a lower black level when the peak luminance goes down (either by setting Picture lower, or by displaying 80% or lower white window without reducing Picture control.
Green is exceesive, but Red and Blue are fairly accurate.
I was able to use Custom mode for calibration with dEs all under 4 from 10% to 100%. RGB Tracking is very linear, color temp tracking is very good. But Gamma was 1.65
I also calibrated Cinema mode – couldn’t get it quite as linear as Custom mode but it was fairly good. Gamma measured ~1.75.
The problem is: If you enter Service Mode and measure the gray scale, you get a Gamma of 2.6-2.75 – Service Mode jumps to a very vivid mode every time you open it, so you have to be careful to re-selet Custom or Cinema – which I was. I was surprised to note that the Gamma in service mode is so different than the Gamma in user mode.
If you are in normal User Mode and measure gray scale, you get a Gamma of 1.7-1.85. I could find NOTHING that would impact Gamma in User Mode. I have the 100% white window set for 26 fL to avoid the black level jumping and because more luminance that that isn’t really needed for this display. I did increase 100% white window luminance to 38 fL and measured Gamma again and still got 1.85.
That said, I should reveal that the owner is an AVS forum participant and has a low-end meter and software, the service manual, and has been mucking about with the adjustments. He had settings where he measured a Gamma closer to 2.5 in User Mode, but didn’t write down anything but cuts and gains. I improved significantly on his gray scale, but could not get Gamma right at the same time. I have no idea if there’s something he may have done in the Service Menu to leave the display with this low gamma problem, but it doesn’t look like it.
The secondaries are pretty inaccurate on these displays with no adjustments – Tint rotates all of them around the triangle. Yellow is clockwise from the ideal point while Cyan and Magenta are counter-clockwise from the ideal points. So if you try to use Tint to make the secondaries better, you either improve Cyan and Magenta while making Yellow worse, or you improve Yellow while making Cyan and Magenta worse. The 0 point puts all 3 in roughly equally bad locations. The Color control is very strange – the colors change drastically as you decrease it to the point where Red turns brown and the measured color space can be 1/3 smaller than the HDTV triangle! The whole right side of the HDTV color space is missing when you turn Color down far enough.
I learned you are not supposed to set the “weakest” color higher than “FC” (hex) when adjusting DRIVES. In this case, Red was weakest at high luminance levels (but still only about 26 fL so the panel is not being pushed). And Red did need to be set to FC while Blue and Green were reduced to bring them in line with Red.
Anyway – I HATE leaving this panel with a Gamma that bad – especially when it can do a Gamma of 2.6 or so when the Service Menu is active. I did not see any adjustment in the service menu that appeared to have anything to do with gamma – but perhaps the code is not obvious?
Does anybody here have detailed info about this panel series that would help me improve the panel’s Gamma? I can’t help believing that if you can get Gamma to 2.6 in the Service Menu, there has to be something that can be done to get Gamma from 1.8 back up to 2.5 or so in normal User Mode.
If not, are there any technical support contacts at Panasonic available for calibrators to call and discuss problems?
Or maybe THX has contacts at Panasonic that might be able to help me with a resource for improving this panel?
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