Dell E7450 LA -A961P - diagnostics after flooding and damaged PD817, PD5 diodes

[bpjl]

Hi,

I have La-A961P Rev: 1.0 (A00) from a flooded laptop on the table. The computer was flooded with tea and at the same time the power supply was disconnected, the battery was removed immediately and the laptop was turned upside down.

I looked at the mainboard, but I don't see any marks of water damage. Maybe the liquid did not reach MB, or maybe I just don't see it.
During the inspection, I noticed a burned (charred on one side) double diode PD817.



Voltage drops during PD817 measurements:
- PIN1-PIN3 forward biased = 0.137V
- PIN1-PIN3 reverse biased = 0.137V
- PIN2-PIN3 forward biased = 0.445V
- PIN2-PIN3 reverse biased = OL

After removing PD817, the resistance between the fields where it was soldered, increased to over 20MΩ. Same between PIN 1 and GND and 2 and GND. Between 3 and GND is about 100kΩ.

I also measured the resistance on the power socket and was only 5Ω. The reason was the PD5 diode.



After its removal, the resistance on the power socket increased to 115kΩ.

Another resistance measurements against GND:
- +dc_in_ss = over 20MΩ
- +3.3v_alw = 11kΩ
- +5v_alw = 25kΩ
- coil from VC_Core = 70Ω
- all other coils = the resistance goes in kΩ
- 8 leg of SPI = 117kΩ

Since the PD5 was damaged, I also made PQ2 and PQ3 measurements:
PQ2:
- D-S - resistance: over 130kΩ in both directions, voltage drop: + on S = 0,559V, - on S = OL
- D-G - resistance: over 140kΩ in both directions, voltage drop: OL in both directions
- S-G - resistance: 47kΩ in both directions, voltage drop: OL in both directions

PQ3:
- C-B - resistance: over 47kΩ in both directions, voltage drop: + on C = 0,643V, - on C = OL
- C-E - resistance: over 35kΩ in both directions, voltage drop: + on C = OL, - on C = 1,922V
- B-E - resistance: 14,9kΩ in both directions, voltage drop: + on B = 0,67V, - on B = OL

What else should I check before trying to power on this mainboard?

[mon2]

Voltage drops during PD817 measurements:
- PIN1-PIN3 forward biased = 0.137V
- PIN1-PIN3 reverse biased = 0.137V

Replace PD817. The diode should not conduct in both directions.

[bpjl]

After replacing the PD817 diode, the laptop turned on and gave the picture on screen.