Hp compaq nc6400 hatoo la-2951p power issue

[vettouch]

I have this laptop that suddenly developed some power faults. The adapter gives the normal rated voltage, but if it is connected to the board, there is no 3.3v or any other voltage. some few resistors and capacitors near the PCN1 have their values below their rating on the board but off-board, they read normal. Also, PL1, PQ3, PQ4 are getting very hot. How can I test and isolate the fault? See the schematic I am working with. My board screenshots also attached.

[mon2]

Re: Hp compaq nc6400 hatoo la-2951p power issue

You are on the right part of the review - PQ3 and PQ4 are the usual suspects - see the detailed thread above from @Piernov.

Remove all power / no battery.

Meter in resistance mode.

Check the resistance across each mosfet:

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

Post the reading in ohms and also the scale used for the measurement on your meter.

Repeat for PQ4. Very likely that at least one or both of these mosfets is defective. If available, you can skip ahead and replace them both for testing.

Also, on the charger IC (PU2), post the voltages for:

ACDET (pin # 26)
ACDRV# (pin # 25)

[vettouch]

Re: Hp compaq nc6400 hatoo la-2951p power issue

@MON2

readings on metre

@200 ohm, 2000 ohm & 20k ohm, no reading between source and drain pins.

@200k ohm; (1,2,3) and (5,6,7,8) = 69.8

@2000k ohm (1,2,3) and (5,6,7,8) = 69

@2000k ohm (4) and (5,6,7,8) = 271.

I had replica MOSFETS which I used in replacing PQ3 and PQ4, yet, no results (still very hot).

No voltages on ACDET (pin #26) and ACDRV# (pin #25)

After replacing PQ3 and PQ4, mosfets are still hot.

What else do I check and I

[mon2]

Re: Hp compaq nc6400 hatoo la-2951p power issue

Remove PQ4 - power up again.

Are PL1, PQ3 now cool ?

[vettouch]

Re: Hp compaq nc6400 hatoo la-2951p power issue

@mon2

Yes, PL1 and PQ3 now very cool.

[mon2]

Re: Hp compaq nc6400 hatoo la-2951p power issue

Ok. Meter in resistance mode (start with the lowest scale).

Remove all power / no battery.

Check the resistance to ground of pins 1-2-3 of the REMOVED Q4 mosfet.

We are checking if there is a shorted part on the main rail.

Also check the resistance to ground of pins 5-6-7-8 of mosfet @ PQ7.

Post the measurements and scale used on your meter.

[vettouch]

Re: Hp compaq nc6400 hatoo la-2951p power issue

@mon2

MY METRE IN RESISTANCE MODE

check: resistance to ground

PQ4

@200 OHM; pins (1,2,3) = 1.3ohm each
@2000ohm; pins (1,2,3) = 1ohm (001 on metre)
@20k ohm; pins (1,2,3) = 0.01 ohm each
@200k ohm; pins (1,2,3) = 00.0 ohm each
@2000k ohm; pins (1,2,3) = 000 ohm each

PQ7

@200 ohm; pins (5,6,7,8) = no reading
@2000 ohm; pins (5,6,7,8) = 511
@20k ohm; pins (5,6,7,8) = no reading
@200k ohm; pins (5,6,7,8) = 71.6
@2000k ohm; pins (5,6,7,8) = 048

[DanielDacko]

Re: Hp compaq nc6400 hatoo la-2951p power issue

@mon2

MY METRE IN RESISTANCE MODE

check: resistance to ground

PQ4

@200 OHM; pins (1,2,3) = 1.3ohm each
@2000ohm; pins (1,2,3) = 1ohm (001 on metre)
@20k ohm; pins (1,2,3) = 0.01 ohm each
@200k ohm; pins (1,2,3) = 00.0 ohm each
@2000k ohm; pins (1,2,3) = 000 ohm each

Inject 1V on pins 1,2,3 with lab PSU and see what heats up. Probably some ceramic capacitor.

[vettouch]

Re: Hp compaq nc6400 hatoo la-2951p power issue

@DanielDacko

I don't have Lab PSU.

[vettouch]

Re: Hp compaq nc6400 hatoo la-2951p power issue

@DanielDacko. As I don't have Lab PSU, what alternative using multimetre will I use to diagnose?

[DanielDacko]

Re: Hp compaq nc6400 hatoo la-2951p power issue

Multimeter won't help you in this case and it's just time wasting, fastest way is injecting voltage on the shorted rail. What can I tell you except to get lab psu or remove part by part to see when the short is gone. You can't use desktop psu since this is a dead short and the psu won't even start.