Re: Serious Val Problem with Panasonic TH-42PX75U plasma

[Anonymous]

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.