Build Your Own Arcade Controls Forum
Main => Monitor/Video Forum => Topic started by: kardenm on August 05, 2010, 11:02:45 am
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Ok.
This is a board I just repaired pwr supply section (blown components/transistors, etc). Picture is pretty decent but is somewhat to dim (cant adjust brightness high enough). Also there is a darker area (faded) on Right side of screen. (degauss did not help)
I have tested or replaced most of the larger caps (all 800's, some 300's and 400's). Where should I go next? More caps?
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check r403,404 , c411 in abl
and d302,c343
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Thanks qrz. Will do and let you know.
By the way, what does ABL stand for?
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All those parts test good along with others I checked while I was at it.
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Thanks qrz. Will do and let you know.
By the way, what does ABL stand for?
"automatic brightness limiter" ;)
will have another look at the print and get back w/u...
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Checked all the components in brightness circuit, all test good.
(D301,302,303)
(R364,366,367,376,403,404,424,425)
(C348,355,369,411)
(Q310).
Is it possible to change one of these components (a resistor maybe) to give just a little more brightness?
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has the crt's cathode current been checked ?
'bout the only thing left is a weak crt.
for fun , pull one side of the fil resistor on the neck board .33 ohm/2W.
loop FOUR turns of insulated wire around the flyback core ( exposed ferrite opposite main xformer)
ground one side of the loop , connect the other to the filament . and u just made a filament winding ;)
when powered, approx 8 volts will be applied to the filaments . approx 2 volts per turn
IF the crt is weak, there may be a noticable increase in brightness. the rejuvenation process would then
be warranted .
no change could be another issue or crt may be to far gone :(
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Thanks qrz. I'll give it a try. Sounds interesting and I like to experiment. I'll let you know.
I know that the problem is not with the crt. I have another (identical) board which displays on this same crt with normal brightness. Got to be something on the board. Right??
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process of elimination.
yes . if crt is fine on another board , the original pcb has to have a fault.
just a matter of finding it
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qrz: Thanks for all your help.
I think I have things squared away now. I found another, bare CRT and hooked this board to it. Works great! The other, "good" board works well with the original CRT although I have to keep brightness adjustments at max to get a good picture.
My conclusions are that the original CRT and the repaired board are BOTH marginal when it comes to brightness. The good b CRToard works ok with the marginal CRT and the marginal board works well with the good CRT. So now I have two useable monitors. Problem solved for (for now) and the boss is happy.
I do wonder if there is anything I can do to improve brightness on the marginal CRT. It's good enough for now but will it get dimmer as time goes on? Is that just something I have to live with? I can probably keep repairing the boards forever but what is the usual life of such a CRT?
I never did try the experiment you suggested but could do that if you think that will tell me something useful.
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sure sounds like a weak crt .
if u don't have access to rejuvenator , or can build one , then boost the filament voltage .
that is what happens on a rejuve anyway. when voltage is applied, it causes a sudden high current ( 100ma)
surge. this often will "blow off crud" from the cathode restoring operable parameters
still just a "bandaid" for the problem ;)
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Think I'll leve this one for now. Picture is acceptable and lots of other stuff to do.
Thanks again qrz for all your help.