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820-3437 - No backlight or image.

gcain

gcain

New member
Works with an external screen.

If I press on Q7707 I get a backlight with a white screen. Only works when pressing with my finger though, not a spudger or tweezers.... I tried just flexing the board too in case that's what I was indirectly doing.

Either way, when I get a backlight, there is still no image, just a white screen. Which should be black on this model I think.

Any suggestions, I can't nail down what the issue is. Solder all looks clean and tidy; if it were the solder it would work when pressing down with anything...
 
D

dukefawks

Administrator
History? Known good LCD? L8304 voltage present? Test while turning it on, it should give a pulse or stay high
 
gcain

gcain

New member
Hi Duke.

No history. Was given to me by another shop who didn't recorded anything.
Board looks spotless. Known good test screens.

L8304 reads 0.02v consistently. Maybe my DM isn't quick enough to get the pulse.
 
gcain

gcain

New member
Not that I can detect.


I sort of think my finger is shorting something when I press on Q7707.
 
gcain

gcain

New member
If I touch R7789::2 or Q7707::3 with tweezers the back light turns on, but only if I'm earthed to the board somewhere...

R7789::1 = 8.32v
::2 = 8.19v
 
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dukefawks

Administrator
Image is the first thing you need, stop messing with the backlight for now. EDP_PANEL_PWR should do something during power on, as the LCD needs power to be recognized. Compare to a known good board if possible to see if your meter is fast enough.
 
gcain

gcain

New member
Tested with a known working board.

R1431, on the good board goes to 3.3v. On the faulty board it stays at 0.3mV.

Does EDP_PANEL_PWR come from the CPU?

I jumper R1431::2 to a 3v rail, I can see the LCD panel reacting. No bkl though, so not sure what is doing. Will that initiate the image sequence or is there more to the missing EDP_PANEL_PWR?
 
gcain

gcain

New member
Maybe my test screen is damaged.
When I shorted the 3v to R1431 it just gave me a grey screen again. Connecting the customers screen gives me a nice crisp image. :)

Is running a jumper an acceptable repair, or should I be repairing it somewhere else?
It seems like EDP_PANEL_PWR comes from the CPU.
 
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dukefawks

Administrator
That's too low I think. Traveling at the moment so cannot compare to working board. Could very well be a dead U8300.
 
gcain

gcain

New member
dukefawks said:
That's too low I think. Traveling at the moment so cannot compare to working board. Could very well be a dead U8300.
Click to expand...

Yep, I get .507 on a known good board.

I think this can be marked solved. I know what the issue is, just need to fix it now.

Thanks for you help.
 
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