820-00928: PP20V_USBC cycling on/off (5.18v/0v)

[macRepairAmb]

Hello

Have this board that caming in with no power. 5.18v on PP20V_USBC. U3200, UB300, UB400 all cycle when power is applied to their port. U3100 is steady at 5.18v. Found corrosion on by and around R3108. Cleaned up the corrosion, confirmed the resistors were good. Also replaced U3100 (2 times to confirm replacement chip wasn't DOA). This didn't fix.

Replaced all 4 USBC port chips with the same issue.
Started ohm'ing around and found 1.8ohms on LA640. Removed both LA640 and 650, still reading 1.8 on on LA640(2). Is 1.8 too low or is the GPU shorted?

 

[2informaticos]

I don't exactly know the value on GPU CORE.
1.8 ohm could be normal; should be good if someone confirm in similar board.

Post diode mode (red probe to ground) on PPBUS_G3H and all other big coils.
Don't forget to check L6900 too.

 

[macRepairAmb]

Should PPBUS_G3H have some voltage

PPBUS_G3H - 0.468
L6900 - 0.388
LB150 - 0.296
L2950 - 0.302
L7410/7420 - 0.0095
L7221/7211/7231 - 0.0054
L7330 - 0.0228
LA350 - 0.0487
LA300 - 0.207
LB700 - 0.344
L7030 - 0.348
L8000 - 0.231
L7960 - 0.079
L7660 - 0.397
L7900 - 0.257
L7660 - 0.445
L8410 - 0.885

 

[2informaticos]

Remove F7000 and check if get some voltage at its pad 1.
Also post exact PP3V3_G3H voltage.
Check SMC_RESET_L and BUF_SMC_RESET_L too.

 

[macRepairAmb]

PP3V3_G3H - 3.41 and stable when power on U3100. Pulsing down to 0.4 when powered by U3200.

Remove F7000 and 7001. Getting 0.05 on both the steady usbc port and the pulsing one.

SMC_RESET_L/BUF_SMC_RESET_L - getting steady 3.4 with steady usbc port and pulsing on pulsing one.

 

[2informaticos]

You must have some problem on USB-C ports.
All ports should have the same behaviour; even if machine not working.

 

[macRepairAmb]

you were right. Found a missing resistor that's not called out in the schematic or board view. It appears the board view for this board isn't correct. It looks like its the board view for 820-00281. To the left of R3109 is a 100Kohm resistor. So when i saw this resistor, i assumed it was taking the place of R3109 (R3109 was actually missing). Anyway, went ahead and installed the 1Mohm resistor for R3109 and that did the trick.

So, this also means that 1.8ohm resistance reading on LA640 and 650 are the expected reading.

Anyway, thanks for the assist.

 

[2informaticos]

Glad to hear you've solved it.
If you still have access on this board, can you please post diode mode on all big coils?
This will help a lot other people.
BTW, post ohm scale value for readings lower than 010 in diode mode.

 

[macRepairAmb]

L6900 - 0.388
LB150 - 0.296
L2950 - 0.302
L7410 - 0.0095/5.34ohm
L7420 - 0.0095/5.30ohm
L7221 - 0.0054/2.51ohms
L7211 - 0.0054/2.58ohm
L7231 - 0.0054/2.52ohm
L7330 - 0.0228/11.72ohm
LA350 - 0.0487/23.5ohm
LA300 - 0.207
LB700 - 0.344
L7030 - 0.348
L8000 - 0.231
L7960 - 0.079/32ohm
L7660 - 0.397
L7900 - 0.257
L7660 - 0.445
L8410 - 0.885
LA640 - 0.0049/2ohms
LA650 - 0.0048/2ohms

 

[2informaticos]

Many thanks, this is very usefull information...