820-01521-02

[Outofwhack]

No evidence of corrosion.
Stuck at 5v, fan runs a while

U3200 CD3215 had open loop D+/D-, replaced, now getting to 20v

Still no logo display.

pp5v_g3s had low diode mode. 5volts injected. C7675 getting hot so removed. DM on pp5v_g3s still .09v
Removed pp5v_g3s inductor, problem downstream of inductor.
Removed all caps downstream and could not find cause of low diode mode .09

Voltages
------------
ppbus steady 12.6v
ppvbat_g3h_conn 12.6v with occasional (5% duty) drop to 0.15v (no bat connected)
5v pp5v_g3s
3.3v pp3v3_g3h
1.2v pp1v2_s3
0v all vcore phases
2.5v 2v7_nand

Checks
----------
vcore mosfets all supplied with 12.6v
0v cpucore_fccm/zcd_en
1.8v all_sys_pwrgd
1.8v cpuvr_pwrgd

Out of steam. Any thoughts?

 

[2informaticos]

Did you test diode mode on 5V_G3S with board alone on the desk?

 

[Outofwhack]

Yes, everything disconnected.

 

[2informaticos]

Inject 5V again and check with good thermal camera.
Nothing will get really hot, but should be able to detect some component with higher thermal signature.

 

[Outofwhack]

When injecting 5v previously I did see a row of 4 resistors getting mildly hot (around 40c) near the chip marked as U2120 on my 820-01521 2018 boardview The row of 4 resistors does not appear on the schematic and U2120 on my board is a 6pin chip.

I will attached a photo of them shortly.

I did remove all those resistors/caps and the chip but that did NOT change the low DM value. I replaced all the components with those off a donor board.

 

[Outofwhack]

I can confirm those resistors are the only thing glowing on the board when 5v injected.
Do you have the schematic that includes those resistors and the 6pin U2120 ?

 

[Outofwhack]

CPU_VCCSENSE_N DM is 0.000v with U7100, C7122 and R0821 removed.

But so it is on a donor board.

Ive swapped U7100 with one off a donor board but no change.