Microsoft Surface Pro (5th gen) model 1796 - no power

[PantherDave]

Hi all!

I'm trying to troubleshoot a Microsoft Surface Pro (5th gen) model 1796 that won't power on. Motherboard model is M1007506-015. My priority is retrieving data, but the SSD is integrated so it looks like if I can't repair it it'll need to go to a data recovery company. I've done a little basic board repair before, but nothing this advanced until now. So please forgive my ignorance in advance. 😅

I found the boardview for this laptop in the forums here, and am able to open it on my PC with FlexBV.
https://www.badcaps.net/forum/troubl...o-1796-calgary

I also found this helpful thread with a similar issue
https://www.badcaps.net/forum/troubl...-1796-no-power

I learned a lot there, and there's a helpful power on sequence from mon2 in post #7.

I have the motherboard removed, with only power adapter and power button board connected. The power adapter supplies 15V. The battery is unconnected. I tested voltages with the black lead to ground and red to various components, using test pads where possible.

Power on sequence step 1 says “Convert any raw power to +3P3VAS” The diagram says this is at “Switch (Diode). I found two sizable diodes near each other. I'll call the one nearer the power adapter diode 1, which I believe receives the power from said adapter.
Diode 1 anode - 15V
Diode 1 cathode - 14.8V
Diode 2 anode - 8.75V
Diode 2 cathode - 14.8V

Power on sequence step 2 says “+3P3V_SAM / Generate SAM's power” I believe that means a step-down converter will send 3.3V to the SAM chip, which seems to be Microsoft's “system aggregator module” which controls power policy. I couldn't find anything in the boardview for “+3P3V_SAM”, but I did find it as “3V3_SAM” - 3.29V
Power on sequence step 3 SAM_RESET# (initialize SAM) - 3.26V
Power on sequence step 4 +VSYS (Declare system power ready) - 8.75V
Power on sequence step 5 Intentionally unused
Power on sequence step 6 PCH_DPWROK (Declare deep power good to PCH) - Extremely small and hard to test, but looked like 0V
Power on sequence step 7 SLP_SUS# (Request standby power) - 0.066V
Power on sequence step 8 VSUS_ON (SAM turns on standby power) Hard to test and get a consistent reading, but it peaked at about 0.09V
Power on sequence step 9 ALL_SUS_PWRGD (Standby power stable) - 0V
Power on sequence step 10 RSMRST# (Declare SUS power good to PCH - 0V
Power on sequence step 11 Intentionally unused
Power on sequence step 12 PWRBTN# - I'm assuming that this refers to the power button, so any steps beyond here would need to be tested differently? Anyways, the problem seems to be earlier in the sequence.
Skipping all the way to power on sequence step 24 is PLTRST# - 0V (of course)

I checked the large coils, found no power to any of them.

I also disconnected the power supply and documented resistance readings from the inductors to ground. I'm using an old Micronta 22-191 digital multimeter, holding a pin against the positive lead to extend it into tight spaces. I had a little trouble getting consistent readings, but here's what I measured. I numbered them in the image below for reference.

#1 1.9 M ohm
#2 160 ohm
#3 100 ohm
#4 43 K ohm
#5 10 ohm
#6 5 ohm
#7 5 ohm
#8 32 K ohm
#9 350 ohm
#10 1.2 M ohm
#11 40k ohm

At this point I'm a bit lost, so any help to point me in the right direction would be much appreciated!

[mon2]

Do you have the schematics?

[PantherDave]

Nope, do you know where I could get them?

[PantherDave]

Okay, I'm looking at a power flow diagram now. From what I measured before, the power is good up to +VSYS. From there it takes 14 different paths, mostly through resisters then buck converters... I can locate these on the board diagram. Cool.

+VCCIO
+1P2V_DUAL
+1VSB
+1P8VSB
+VCORE
+VCCSA
+5VSB
+3P3VSB
+3P3V_SSD
+VCC_EDP_BKLT_OUT
+VCCGT
(IR Illuminator) D4902
+VCCEDRAM
+VCCEOPIO

Looks like I have some more probing to do. Hook up power adapter and test for voltage on each path?

[mon2]

Yes. If a voltage is absent, check if the rail has the enable voltage. Check the resistance to ground but with no power.

[PantherDave]

Okay, so I was getting no voltages on any of those paths. Evidently I was misled by Power On Sequence step #12 - PWRBTN. I thought that was the point where you need to press the power button? So, knowing that... I retested a few things. I even retested step #24 PLTRST, which I obviously didn't test correctly before. I found 2.29V. Over on the other thread I mentioned, j64x86 said this should be at least 5V, but I'm not sure where he got that information. How do I find out what voltage it should be?

And if it's actually good to that point, where does that leave us? Before disassembling, I couldn't find any power light and there was no indication of any functioning video output. I also checked with a flashlight in case of a backlight issue. Wondering if I should buy a Mini DisplayPort adapter at this point to make sure it also won't give video out that port.

[PantherDave]

Oops, meant 3.29V.