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Main => Monitor/Video Forum => Topic started by: epraiser123 on January 16, 2008, 11:40:05 am

Title: Pentranic CH-288, Monitor needs brightness, bright=red&smear, dim=good picture
Post by: epraiser123 on January 16, 2008, 11:40:05 am

Hi all,


My Monitor:
Pentranic 40" CRt monitor with Chassis CH-288 (from a Gauntlet Legends)
I believe sticker on Tube says A89PNT30X (tube&chasis Assembly)


Tested /w MAME AcadeVGA /w JPAC (has video amp) and Tekken 4 Jamma PCB with same results.



My Problem:

I can adjust my brightness pot up but when I do I see a red'ish tint to everything, ie the black background would look redish, if I reduce my brightness the red tint goes away.  But then I adjust for the color smearing with the  contrast so there is no smear but the end result is a very dim picture but the picture is good.  If I want to make it brighter I have to either sacrifice to have some color smearing or have a red tint . 

Now the neck board has a subbrightness pot I played with in tanget to the flyback brightness pot, there is a red-bais and blue-bais, r b g gains but I couldn't find a combination that could fix things. 

Now if I crank up the brightness the crt tube is bright so I would think my tube doesn't have an issue and that the brightness is being hampered by some issue on the chassis. 

I did order radial ElectroCaps to replace all the ones on the board and I have finished with 90% of those replacements.  The screen is a little brighter but still noticable dim when I adjust for a clear picture, I don't want to sacrifice a crumpy picture for brightness, I would like to have both,

anyone have any ideas? a resistor or something? flyback? what could I look into?

Here is the chasis 1 pg schematic...

CH-288 Schematic Here:
http://home.comcast.net/~dsouzajr/CH288.pdf (http://home.comcast.net/~dsouzajr/CH288.pdf)


THANKS ALL!   :notworthy:

Title: Re: Pentranic CH-288, Monitor needs brightness, bright=red&smear, dim=good picture
Post by: grantspain on January 16, 2008, 02:08:04 pm

whats happens when;
a-you remove the red video signal
b-you remove the red drive transistor

Title: Re: Pentranic CH-288, Monitor needs brightness, bright=red&smear, dim=good picture
Post by: qrz on January 16, 2008, 04:59:39 pm

initiially,  sounds like a weak crt .
however,
high ESR on c701-3 , c710 may cause video problems.
u may also wish to check Q701, 702 and Q107, 108
Q107/8 are part of blanking and brightness limiter circuits

btw, tnx for the print

qrz

Title: Re: Pentranic CH-288, Monitor needs brightness, bright=red&smear, dim=good picture
Post by: Rickn on January 17, 2008, 06:35:00 am

Yes, considering this monitor must be at least 7 years o;d and probably more it is very likely a weak CRT. I assume this is a problem that has slowly got worse.

If you have access to a tube tester, that is what I would suggest before spending too much time and $$$ but I do.

By the tube number it is likely dual focus so that may be a problem.

As I mentioned in my e-mail to you yesterday, call me at work between say 8am and 2pm EST and we can talk it through to see if there is another route.

Do not know where you are located, but if need be we would be happy to test the board and confrim tube or board.

Good Luck
Rick Nieman
Nieman Video Displays
www.Niemandisplays.com
519-621-1722