Serious Val Problem with Panasonic TH-42PX75U plasma

Serious Val Problem with Panasonic TH-42PX75U plasma

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  • #159

    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?

Viewing 11 replies - 1 through 11 (of 11 total)
  • Author
  • #905
    Gregg Loewen

    Hi Doug

    No sense in measuring primaries and secondaries if you can not adjustment. It is like starting to obsess over things that you have no control over. (becareful).

    When you enter the service mode the set defaults to vivid mode (or whatever). Once you get to the drive / cuts then you will have to reselect the cinema mode to calibrate.

    Hope this helps??

    Perhaps Michael can chime in.



    If you look at the blacks in the SM, they are being crushed … usually.

    The SM is only the place to do the grayscale and pop out to take real readings. Then back in again for more changes and so forth.

    I have gotten decent Gamma when setting the stuff up in the cinema mode … which is usually the darkest. for light controlled rooms.



    It was obvious I couldn’t do measurements while in the Service Menu the first time I did an exploratory measurement in Service Menu mode (I’d already measured the same thing before I went in to Service Menu mode), so, yes, I was already doing the measurements outside the Service Menu mode and only going into Service Menu to make changes to cuts/gains.

    That method is what produced the measured Gammas of 1.65 for Custom mode and 1.85 for Cinema mode. As mentioned in the first post, I have very low post-calibration dEs from 10% to 100% in both Cinema and Custom which is reflected in nice flat temperature graphs and RGB graphs. I just couldn’t get Gamma anywhere close to 2.2-2.5. At least not while minimizing that goofy floating black problem (black level jumps up very noticeably if 100% white window luminance is set higher than 29 fL). The owner of the display, being the tweak he is, did his own calibration in January and measured 2.5 Gamma, but he had bad floating black issues and his RGB and temp graphs were far worse than what I left him with. His Gamma graph showed the 3 colors separating as luminance increased (the 3 colors were not tracking the same gamma curve). And his 10% step was very red which was incredibly obvious in movies. I’m beginning to think my “perfect settings” for the gray scale and elimination of the floating black problem put the display into a place where it simply can’t do Gamma. The owner specifically asked me (before the calibration) to eliminate the floating blacks and the bad red tint he had at 10% – and I did both of those. The cost appears to have been Gamma coming out at 1.65 in Custom mode and 1.85 in Cinema mode.

    Does this sound possible/plausible?

    Something else I noticed while looking through the service manual… it has you set Green Drives to C0 (C_Zero) (hex) and do all the adjustments with Red and Blue where it describes setting the setting factory color temps. Green Cuts also have a specific setting with all adjustments performed on Red & Blue Cuts. I did change the Green Drive settings a fair bit and Green Cut was adjusted a little to get the ideal gray scale tracking. Any possibility setting the Drives and Cuts back to the numbers specified in the Service Manual would put Gamma back to something more reasonable? I doubt I’ll be able to get the gray scale nearly as accurate without being able to tweak Green though… Red was “weak” compared to the other colors at high luminance (even though I was only getting 26 fL from the 100% white window) so I was reducing Blue and Green Gains a fair bit to get them in line with Red.

    Gregg Loewen

    you will have to set the black level on a low level APL pattern, other wise dark scenes will look like crap.

    removing red from 10 ire should only take a click or 2 from the cut controls, and or a click or 2 from the black level control.


    If it wasn’t clear, I did set black level using 0% and checked it with 10%, 20% and 30% to see how it held up… it was OK throughout.

    The black level only jumped up when you displayed something that “pushed” the panel a bit like the 100% window at 29 fL or more. If you adjusted the Picture control 1-step at a time, there would be a 1-step increment that would cause the black level to jump way up. I ended up using the 100% window to set the luminance to 26 fL to make sure the panel stayed below the threshold where most of the shifting of the black level would not happen.

    But that left me with Gamma at 1.65 in Custom mode and 1.85 in Cinema mode.

    The numbers you mentioned were about right for getting rid of the red tint to the 10% step. I got that under control with no problem.

    My only problem is that as good as every other measurement is after the calibration, Gamma is 1.65 for Custom mode, and 1.85 for Cinema mode. And there are no User controls or service menu controls for Gamma.

    It appears that the only alternative is to put the panel back to the previous settings (where Gamma was 2.4 or 2.5) and leave all the other errors that I “fixed” with my calibration. My gray scale was much better than his – it was actually excellent with very low dEs. So it surprised the heck out of me when Gamma measured as low as it did. But he’s obsessed with the low Gamma. Before the calibration he was obsessed that the 10% step had red in it and that his black levels floated. I got rid of both issues, only to get hammered with the low Gamma.


    If blacks float … then let them float. You can’t re-design the TV. Work on the other stuff …

    Also make sure the client understands that there are no holy grail TVs.

    For fun … take the contrast down really low … and chart the gamma then …

    sometimes you have to pick light output over gamma. Remember to make sure the client does not obsess over graphs.



    “Take contrast down really low”

    How low? I already set the 100% white window to 26 fL. That’s where it is set when measuring Gamma at 1.65 for Custom and 1.85 for Cinema. At about 29 fL (for the 100% white window) the black level jumps up significantly.


    It appears on these panels that if you set the Picture/Contrast and Brightness controls to their mid-point then use sub-bright and sub-contrast in the service menu to setup the black and white levels, the panel’s gamma is somehow thrown for a loop (way too low). Leaving sub-bright and sub-contrast alone in the service menu and using the user menu adjustments seems to produce OK gamma.

    This is preliminary… I will be confirming this in 10 days or so when I go back to have a second shot. I will post a follow-up/update after that return trip.

    Gregg Loewen

    that makes since. ( I guess).

    I center the brightness control and and adjust the contrast control in the user menu. I then adjust the brightness by using the cut all control in the service mode.


    Well, I went back and had another shot at getting a decent combination of Gamma and gray scale. No one thing got the Gamma back from 1.65 to 2.1 where it was when I left.

    I had been using Custom mode on purpose during the first calibration since it gives you more controls and I was getting a better gray scale. Switching to Cinema mode upped Gamma by around 0.2 and I spent more time massaging the gray scale which eventually got better.

    I did move the sub-bright setting back to the 802 default and gave up on having Brightness in the user menu at 0 for easy reference, but that ended up not doing anything useful.

    Moving Cuts & Gains did change Gamma though so I followed the setup procedure outlined in the Service Manual for this model which involves setting all 3 cuts to 80, setting Green Drive to C0 and adjusting only Red Drive and Blue Drive to get d6500 for a 100% white window. Once you have that, set All Drive to FC. Then you can fine tune cuts and drives as long as you don’t exceed FC for the weakest color on the Gain/bright end… so if Red is the weakest color, Red Gain should never be set higher than FC.

    Doing that gave me another .18 or so, getting me back to ~2.03.

    The last thing I tried was crushing the bottom a little. I ended up pushing 1% and 2% into black, 3% was about where you’d expect 1% to be. That gave another .07 so Gamma ended up right around 2.10. But I couldn’t find anything that would get the Gamma any higher than that.

    The picture looked about like you’d expect… a little lost shadow detail, but not too bad. The Green primary is pretty high on these panels… nothing could be done to fix that. All 3 secondaries were “off” with Cyan and Mageta being counterclockwise from the ideal position and Yellow being clockwise from the ideal position, so again, nothing could be done about those.

    With the higher Gamma, I had to give up having the 10% step almost perfect… it went Blue but nothing you could do about it. Forgunately it wasn’t so blue that it was distracting. The extra blue seemed to combat the panel turning very red 4%-6% since that problem disappeared with the new settings – and that red 4%-6% problem was pretty obvious, much worse than the blue-ish 10% step.

    I may never have encountered the low Gamma problem with this panel if the owner hadn’t been calibrating it himself with CalMan and an i1 Display LT – and not writing down the factory defaults for Cuts/Gains. On the first Cal attempt the Cuts in particular were much higher than where they end up if you use that factory procedure. And even though Custom mode lets you do some things better than you can in Cinema mode, the loss of .2 in Gamma whenever you switch to Custom mode compared to Cinema was too much of a handicap with this panel. The gray scale ended up being quite good for 20%-100%, Gamma was much more reasonable at 2.1 and I got rid of that red-shift in the deep shadows that had been bugging the owner.

    He ended up happy, and I felt pretty good about undoing the problem without having recorded factory defaults for the panel.

    Gregg Loewen

    nice ending.

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