820-00165 not booting

[arnonabuurs]

Working on another 00165, this one has green and orange light. Spinning fan but not booting. Display doesnt light up, there is 8.57v on the fuse but not boosting, but display not turning on at all so it seems. Tried PRAM reset nothing happens. Tried to boot with external drive on external display, nothing happening. External drive and mouse have led activity.

History was I repaired it about a month ago, short on C7319 but that looks all good, no short and power is working.

 

[2informaticos]

So PRAM/SMC reset no reaction at Magsafe light, nor at USB LEDs?
Really strange, if you confirm USB activity...

Post voltage for J8300, 2, 3, 14, 15, 16, 18/19.

 

[arnonabuurs]

Tried the reset it does seem to reboot as USB drive switch off and then turn on again. As for display circuit no voltages, only get 8.59 on fuse but voltage for J8300, 3, 4, 14, 15, 16, 18/19 all 0. Cannot find any shorts in display circuit, seems its not turning on? Should have at least 8.59 on pin 3-4 i guess unless the line is broken, but no short.

 

[2informaticos]

"Should have at least 8.59 on pin 3-4 i guess"
NO, until Q7706 is enabled.

This board has DP connection for LCD, so 3V is required at pins 18/19 of J8300 in the first few seconds.
Then pin 14 must go high so, PCH can detect LCD.
If not, pins 18/19 drop to 0V.

Check traces from R5670 to J/U8300.
Be sure L8304 and R8360 are OK.