Precision 5550 LA-J191P No Power, Burnt ISL9538

[swimllamaswim]

Review the voltage to ground @ PL1901 (either side).

It's at a locked 0.9mv

[mon2]

Assuming that you have ~20v on the CHG_SRC_20V -> Then the mosfets linked to this inductor are suspects = PQ1902, PQ1900, PQ1903, PQ1904.

Remove all power. Meter in resistance mode. First confirm that the main power rail is not shorted. Test the resistance to ground of B+. This must be a high resistance else there is a fault here.

Next..

Test each mosfet using resistance mode.

Measure:

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Each must be hundreds of k ohms or higher else could be defective. Repeat for each mosfet.

[swimllamaswim]

Assuming that you have ~20v on the CHG_SRC_20V -> Then the mosfets linked to this inductor are suspects = PQ1902, PQ1900, PQ1903, PQ1904.

Remove all power. Meter in resistance mode. First confirm that the main power rail is not shorted. Test the resistance to ground of B+. This must be a high resistance else there is a fault here.

Next..

Test each mosfet using resistance mode.

Measure:

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Each must be hundreds of k ohms or higher else could be defective. Repeat for each mosfet.

B+ looks good, at 4 megaohms. However, all four mostfets were shorted in some way. I'll get replacements on the way for those, but in the meantime, is there anything else I should check, that those could have affected? And for the 3rd Type C port running at 5v, I'm assuming that's the PD chip, correct? Do those need to be programmed?

PQ1900:

[B]source (1-2-3) & drain (5-6-7-8) - 75kohm
source (1-2-3) & gate (4) - 1.7ohm
gate (4) & drain (5-6-7-8) - 100kohm

PQ1902:

source (1-2-3) & drain (5-6-7-8) - 100kohm
source (1-2-3) & gate (4) - 1.7ohm
gate (4) & drain (5-6-7-8) - 100kohm

PQ1903:

source (1-2-3) & drain (5-6-7-8) - 37kohm
source (1-2-3) & gate (4) - 50kohm
gate (4) & drain (5-6-7-8) - 0.5ohm (resistance of my leads)

PQ1904:

source (1-2-3) & drain (5-6-7-8) - 50kohm
source (1-2-3) & gate (4) - 1.7ohm
gate (4) & drain (5-6-7-8) - 50kohm