WG 19K7302 dim picture

[kardenm]

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?

[qrz]

check r403,404 , c411 in abl
and d302,c343

[kardenm]

Thanks qrz.  Will do and let you know.

By the way, what does ABL stand for?

[kardenm]

All those parts test good along with others I checked while I was at it.

[qrz]

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...

[kardenm]

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?

[qrz]

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 

[kardenm]

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??

[qrz]

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

[kardenm]

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.

[qrz]

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  

[kardenm]

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.