820-00165 - No power. No display.

[ronaldo]

Hi, everyone.

I'm working on this board with liquid damage near U1900, R5614, C1210 and U5800.
I've replaced a few resistors and caps in those areas; some weren't turning on before.
So, after all the work I've done and doing a U.S cleaning. The board now comes on and the fan is spinning at normal behaviour.
All the power lines are present from S5 to S0 except the PPHV_S0SW_LCDBKLT.
But It has no display, so it's not a case of a backlight issue as I've tested with another screen and nothing.
Using a torch behind the Apple logo doesn't make a difference.
No USB activity - USB lit, but not blinking.
Is there any chance that the firmware is corrupt on U6100?
Thanks

 

[2informaticos]

Don't bother with the backlight, as you don't get image, nor even USB activity.

PLT_RESET_L comes high?
Check all SPI Bus Termination resistors and their traces.
Clean/remove J6100, if needed.

You will need to unsolder U6100 for flashing, if remove J6100 first.

 

[ronaldo]

PLT_RESET_L - 3.33V
I know it's a silly question, but should an SPI IC from another logic board work without changing the Serial Number?
I swap the spi ic and same results.
Removed J6100

 

[ronaldo]

Just after posting, I ran another visual inspection on the logic board and discovered a missing resistor, R1540.

I had replaced many of them before performing the U.S. cleaning, but I missed that one, and I believe it might have fallen into the U.C. machine.

I replaced the missing resistors, and now it works fine.

Thanks for the help.

 

[2informaticos]

Yeah, communication between PCH and SMC via LPC bus is mandatory.