820-00165 - No backlight brightness control.

[gcain]

Originally had liquid damage. Swapped the LED Driver.
Worked okay.

Now the backlight is either full brightness, or anything else and it's off.

Guessing some sort of PWM issue?

 

[dukefawks]

First suspect would be the LP8550

 

[gcain]

I already replaced LP8550.

Is there a way to measure it?

 

[dukefawks]

Measure what PWM is doing. But this usually happens when something is shorted together under the LP8550 or a reistor/cap around it.

 

[gcain]

Measure PWM with an oscilloscope?

My DMM is telling me it's 1.46v which I guess is an average of the pulses.

 

[dukefawks]

Did you replace the LP8550 again, did you check for solder blobs/shorts on the components around it? At full brightness PWM should be 3V+

 

[gcain]

I haven't replaced it again, have finally run out of LP8550s.

For some reason nearly every job the last ten days has been LP8550 related one way or another.