AVS Forum banner

Status
Not open for further replies.
1 - 4 of 4 Posts

·
Premium Member
Joined
·
4,176 Posts
Discussion Starter · #1 ·
Hi,


I am visiting a friend's place in Boston, and I happen to be helping him touch up his Sony G70 CRT projector. Got the convergence and focus improved, but now I need a memory refresh on adjusting G2, Bias and Gain (all are accessible on this G70).


After doing my best so far using the AVIA 10 step greyscale bars pattern, I can still see a slight bluish tint in the middle 50 IRE bar and surrounding bars, when the 20/30 IRE and 80/90 IRE looks good enough to my eyes, at least better than the way it was earlier. I would use a meter, but I don't have ColorFacts or any appropriate software with me here.

On the G70 CRT projector, what combination of adjusting G2, Bias and Gain (upwards or downwards, and on which primary color?) will reduce the bluish tint in the midlevel greys? That is, while being able to maintain the white and the dark greys, because they look acceptable within limitations of the human eye.


I've been out of practice calibrating CRT's since I own a G1000 DILA at home - more convenient for my needs due to my moving 4 times in the last 2 years. Chris Williams, Guy Kuo, etcetera, if you have posted any information on greyscale calibration before, can you please kindly provide this info again -- it seems that some of Guy Kuo's articles no longer show up in a search. :-/


This information is muchly appreciated to refresh my memory -- thanks!! :)
 

·
Registered
Joined
·
4,916 Posts
Mark,

If your friend has the early firmware on his CRT, you can manually adjust the G2 for RG & B using the remote. In the servicemans mode hit the bias key twice and you will see G2 adjustments.

Now getting the "hump" as you put it out of the G-70 is very difficult to do by eye. It is a very iterative process of going back and forth between bias and gain to try and make the CRT behave in a more linier fashion. You can alo try defocusing the blue to get it to saturate better on the high end which will allow you to bring the B Gain and Bias down a but. That might help.

But doing it by eye. I know you have a good one but it's tough.

Some of the folks I know that don't have a colorometer do a reset on the Gain and Bias and take it back to factory defaults and claim good results.


Trator!!


Terry
 

·
Premium Member
Joined
·
4,176 Posts
Discussion Starter · #3 ·
Thanks, this may help. I've gotten it closer already. I had to remember

if I had to alternate between Bias and G2, or instead alternate between Bias and Gain. Along these lines, is it safe to increase G2 higher (and adjust Bias to compensate) -- I seem to recall some cautions about G2.


I am enjoying calibrating a CRT for the first time in a while... though I don't think I'll part with my G1000! ;)
 

·
Registered
Joined
·
1,214 Posts
Mark,


It's Bias and Gain. G2 shouldn't be set too far out of the spec, and bias does what you're trying to do with G2.


All CRT projectors have a blue hump because the blue tube can't put out as much light as red and green, so to get whites white with reasonable brightness, you have to turn up blue. As you go down the gray scale levels, the blue output goes up. Try backing off on the blue gain and try defocussing the blue electrically, but remember to defocus in the "correct" direction, and that is found by looking at blue dots at high contrast and defocussing the blue in the direction that causes the dots to become uniformly fat, as opposed to the defocus direction where the dots have a halo around them.


Chuck
 
1 - 4 of 4 Posts
Status
Not open for further replies.
Top