MacBook Pro Retina A1398 shorted PP1v05

[ACS-Repair]

Hello All
I have an 820-3662-A that will not start up. I did a quick short test on the power rails and found that there is a partial short on the PP1v05_S0 rail (measured at L7630). The resistance to ground is 2.5 ohms and it should be more like 70 ohms (compared to another board I have). I have partially lifted L7630 to verify that the short is after the coil. I have injected voltage, starting at 0.5v going up to 1.0v but nothing is getting hot. The PCH gets slightly warm, much like when it's operating. The current at 1.0v is 900mA and unfortunately I can't go higher with voltage. current limit on the power supply is set to 2.5 amps so it's not being limited.
I don't expect anyone to tell me what's wrong but I am interested to see if anyone has had an experience like this and has some insight or recommendations. It would be greatly appreciated.

Power rails:
PPBUS_G2H = 12.6
PP3V42 = 3.43
PP3V3 = 3.34
PP1V5_S0 = 0 (shorted)
PP1v05 = 0
PP5V_S3 = 0

I don't know that any of my missing rails are going to come back without first sorting this out.

[dellxps15]

Re: MacBook Pro Retina A1398 shorted PP1v05

with l7630 removed, try to power on macbook and see if all s5 s4 s3 s0 volts comes.

[ACS-Repair]

Re: MacBook Pro Retina A1398 shorted PP1v05

Hi dellxps15,

I decided to move away from PP1v05 to understand why my seemingly unrelated PP5V_S4 was missing. It looks like you were thinking the same.

These are additional measurements I made this morning before lifting one side of L7630.
PP5V_S3 = 0
PP5V_S4 = 0
PP5V_S5 = 5.03
PP5VS4_EN = 0.09
PP5VS4_PGOOD = 0

After lifting L7630 I had the following.

PP5V_S3 = 5.06
PP5V_S4 = 5.06
PP5V_S5 = 5.03
PP5VS4_EN = 3.37
PP5VS4_PGOOD = 4.27

This has made a difference but I need to investigate to see why. Is this the result you were expecting? Do you think it means that my PCH is the main fault?

[ACS-Repair]

Re: MacBook Pro Retina A1398 shorted PP1v05

I should also mention that this board has no signs of liquid damage. It's very clean and has had no previous attempt to repair. I bought this board as a parts/repair to replace another one that I have. I was hoping it was going to be a relatively easy fix.

[dellxps15]

Re: MacBook Pro Retina A1398 shorted PP1v05

how many omh on Vcore rail ?

[ACS-Repair]

Re: MacBook Pro Retina A1398 shorted PP1v05

CPU VCore coils are 12.2 ohm.

[ACS-Repair]

Re: MacBook Pro Retina A1398 shorted PP1v05

After more testing with L7630 removed.

PP5V_S0 = 5.06
PP1V35_S3 = 1.36
PP1V5_S0 = 1.51
CPUVR_PHASE1 = 0

It looks like most of the main power rails are there. There is no fan spin and no CPU VCORE. I've lifted C7648 and C7649 and measured the load to confirm that these caps are not the problem. There are quite a few 1uf caps around the PCH but I don't know what the likelihood of it being one of these is.