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

[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.

So, after a very, very long wait with customs and incorrect items delivered, I finally got the replacements in. I pulled the old ones, tested the traces, and there's still shorts on, most notably, PQ1903 gate to drain. Any ideas from here? I guess I could have saved some time and pulled the mosfets and tested BEFORE waiting on overseas shipping, but oh well lol.

[mon2]

Remove all power. Meter in resistance mode. What is the resistance between drain & gate pins on PQ1903? Still the low resistance as before?

If yes, flux and lift up one leg of PL1901 - measure the resistance again for the above mosfet - still the same resistance?

If yes, remove PQ1903 and then measure the resistance to ground for the gate driver pin at the charger IC. PU1900 may be defective.