820-00850 No video bad corrosion

[prodigy83]

Board had pretty bad rust and corrosion. At first I was getting video on the built in display, but I stuck the board in my ultrasonic cleaner and now I have no video. I am assuming the ultrasonic cleaner did more harm then good. I am getting no video on the built in display, and no video on an external monitor, however the external monitor does detect a signal. U5450 is heavily damaged. I tried scraping in one area/pin of where one of the pads should be (u5450), but I got to ground. Any hope?

 

[2informaticos]

You can try without Q5450.
But need to trick T2, which supervises LCD backlight current.
Should solder a resistor between pads 6 & 10.
3-6K will simulate a current consumption of 1-2A aprox; test which value works better.

 

[prodigy83]

No go, I did a bit more troubleshooting and I have no EDP_BKLT_EN. Looks like this leads back to the processor. No luck?

 

[2informaticos]

Possibly knocked off component, or broken trace.
This can happens when ultrasonic hard corroded boards; especially if no sweep function used.

 

[prodigy83]

You can try without Q5450.
But need to trick T2, which supervises LCD backlight current.
Should solder a resistor between pads 6 & 10.
3-6K will simulate a current consumption of 1-2A aprox; test which value works better.

Looks like this got it. I ended up using a 5.6k resistor, thank you! Now I just found it is locked down with an Apple ID. ¡Ay, caramba!

 

[2informaticos]

Seems that you've seen was U5450, not Q5450; sorry for error...