820-3115 fan spins but no chime or vcore

[ytesfay80]

This board had a small amount of liquid damage around the SMC area and in that area on the other side of the board I replaced several components around that area and have ultrasonic'd the board.
Initially I started by replacing Q5030/50, R/C5329, C4901/20, R5488/89, C5489
C/U6901, C7782, U7780, R2460/65, C7781
After replacing all those the board was just pulsing and not turning on. I then replaced U7760 and then the board started turning on and the heatsink got warm.

After assembling there was no chime or video on the screen but the fan spun and I was able to turn the machine on and off with the keyboard. I did an SMC and PRAM reset but that didn't help.

I measured PPVCORE_S0_AXG and PPVCORE_S0_CPU but I only get about 0.017v.

The entire U7400 area is spotless and R7402/03 measure the proper resistance and that is from the resistor to the pin on the chip so I made sure the traces are fine.
U7400 Measurements
Pin 1 - 0.53v
Pin 48 - 0.64v
Pin 47 - 3.29v
Pins 46, 29, 19 - 5v

 

[Bouba148]

Hi ytesfay80,
​​​​​​I have the same exact issue with the same board, i'm suspecting the smc.
Do you have ALL_SYS_PWRGD and DDRVTT rails ?

 

[ytesfay80]

I only get 0.13v on ALL_SYS_PWRGD and 0v on PP0V75_S0_DDRVTT.
I figure it might be an issue with the U7760 chip I replaced. I am only getting 0.9v on both sides of R7765 and 0.6v on C7764. I tried putting 2 other U7760 chips from donor boards but the fan wouldn't even turn on and the cpu didn't get warm.

 

[Bouba148]

I don't understand why you're looking at U7760, this one is only providing PP1V8_S0_REG, do you have that rail?
In my case also the CPU is not getting hot ( normal : it's not powered)

 

[ytesfay80]

For some reason when I measured PP1V8_S0 on C7780 & C7762 and get 3.28v.
On R7760 I get 3.26v on Pin 1 and 1.09v on Pin 2. Not sure but these measurements don't seem like what they should be.

I get 0.75v on PPVTTDDR_S3 but 0v on PP0V75_S0_DDRVTT

PP1V5_S3, PP1V5_S0 and PP1V05_S0 all have the proper voltage on them so it looks like the 1V8 rail is the issue.

 

[dukefawks]

ALL_SYS should be present before you even worry about PPVCORE. There must be a rail missing that is keeping ALL_SYS low. If PP1V8_S0_REG is not present then that will at least be a problem!

 

[ytesfay80]

I am getting 3.28v on C7780(PP1V8_S0).
Do you know why it would be so high when it should be 1.8v? Could it be due to the U7760 chip I put on? I didn't have a stencil to reball that chip so I just put solder on the pads and flowed it onto the board.

 

[dukefawks]

3V on 1.8V line is NOT good. Yes of course the problem is a fucked U7760 and now the board is possibly totally fried. Pull of U7760 and put balls on the board then put a clean U7760 from a donor on the balls and pray that the whole thing did not fry with the 3V fuck up.

 

[ytesfay80]

Okay I replaced U7760 with a new one from digi-key(MAX15053EWL+T) and now I has no fan spin and the 5v/3v3 S3 and S0 rails are missing. I checked for pm_slp_s4_l but there is only a quick pulse when the charger plugged in and then 0v afterwards.

The 1V8_S0 line is not shorted to ground in diode mode.
3v3_S0 and 1V8_S0 is no longer connected to each other.

 

[dukefawks]

I'm pretty sure you already killed the CPU or PCH by sending 3V to the 1.8V rail.

 

[ytesfay80]

I removed that chip again from the board and cleaned the pads and now I'm getting a quarter fan spin that keeps trying to turn on every 5 seconds.

Can someone take a picture of the positioning of the U7760 chip on a donor board so I can make sure I am putting this new chip facing the right direction because I don't see any dot on the chip that marks where pin 1 is?

 

[dukefawks]

You already killed the cpu/pch.....