Alienware 18 LA-9332P 3V, 5V short

[Johndill]

Hi, as far as I can tell, this board has a short on 3VALW and 5VALW and I am currently stuck on what to do next.

PU100 gets hot when the AC adapter is connected so I assume it's shorted so I have removed it for testing.

QZ1 is grounded on pins 1, 2, 3, 5, 6, 7, 8.

PQ104 pin 5 grounds the DC jack shorting the AC adapter so I have removed it.

PL102 is grounded on pin 1.

PL101 is grounded on pin 1.

PL501, PL502, PL503 and PL504 are grounded when the CPU is in, they are ungrounded when the CPU is removed.

PL201 is grounded.

QZ3 is grounded on pins 1, 2, 3, 5, 6, 7, 8.

PQ201 is shorting the DC jack also and is removed for testing other stuff.

As far as I can tell, 3VALW and 5VALW are shorted somehow and I have come to an end on where to go next so I;m acking the experts on what could be going on. Thanks :-)

[piernov]

Re: Alienware 18 LA-9332P 3V, 5V short

It's not always safe to remove a buck controller and power on the board because then the gates of the high-side MOSFET are floating, and they could pass current, meaning sending 19V to the 3V or 5V rail. If you need to power on the board with the buck controller removed, either disconnect the PJP jumper, remove the output inductor or remove the high side MOSFET.

Ignore PL501, PL502, PL503 and PL504, it's normal to have low resistance to ground there with CPU inside the socket.

You have several places shorted to ground that should not be shorted together and are mostly unrelated. I'm not sure what happened but this doesn't look good.
It's especially concerning to have PQ201 shorted but for now ignore that circuit as the 3V/5V circuit must be fixed first.


You should try to isolate the shorts as much as possible, so remove QZ1 and QZ3 (which are probably dead anyway) and check which side is shorted for both.

Disconnect PJP100, PJP101 and PJP102 and check which sides are shorted too. If they cannot be disconnected, remove PL101 and PL102.

Also check for a short to ground on pin 3 and pin 13 of PU100.

[Johndill]

Re: Alienware 18 LA-9332P 3V, 5V short

It's not always safe to remove a buck controller and power on the board because then the gates of the high-side MOSFET are floating, and they could pass current, meaning sending 19V to the 3V or 5V rail. If you need to power on the board with the buck controller removed, either disconnect the PJP jumper, remove the output inductor or remove the high side MOSFET.

Ignore PL501, PL502, PL503 and PL504, it's normal to have low resistance to ground there with CPU inside the socket.

You have several places shorted to ground that should not be shorted together and are mostly unrelated. I'm not sure what happened but this doesn't look good.
It's especially concerning to have PQ201 shorted but for now ignore that circuit as the 3V/5V circuit must be fixed first.


You should try to isolate the shorts as much as possible, so remove QZ1 and QZ3 (which are probably dead anyway) and check which side is shorted for both.

Disconnect PJP100, PJP101 and PJP102 and check which sides are shorted too. If they cannot be disconnected, remove PL101 and PL102.

Also check for a short to ground on pin 3 and pin 13 of PU100.

I've replaced everything I removed except PL101 and PL102 as I removed them to isolate the short earlier.

QZ1 removed:
pins 1, 2, 3, 5, 6, 7, 8 shorted, pin 4 good.

QZ3 removed:
pins 1, 2, 3, 5, 6, 7, 8 shorted, pin 4 good.

PL101 already removed:
pin 1 short
pin 2 good

PL102 already removed:
pin 1 short
pin 2 short

PU100:
pin 3 good
pin 13 good
found pin 12 short

cap PC117 short to ground, short was gone when I removed PU100 earlier.

[Johndill]

Re: Alienware 18 LA-9332P 3V, 5V short

Please refresh as I have corrected some mistakes ^^^

[Johndill]

Re: Alienware 18 LA-9332P 3V, 5V short

What should I try next?

[Johndill]

Re: Alienware 18 LA-9332P 3V, 5V short

Bump.

[Johndill]

Re: Alienware 18 LA-9332P 3V, 5V short

I'm not sure what else to test from here, suggestions?

[Johndill]

Re: Alienware 18 LA-9332P 3V, 5V short

Am I alone? It's so cold in here.

[ktmmotocross]

Re: Alienware 18 LA-9332P 3V, 5V short

to be sure u mean short is resistance under 2ohms?

to locate short remove all components where u find shortted pins

[Johndill]

Re: Alienware 18 LA-9332P 3V, 5V short

to be sure u mean short is resistance under 2ohms?

to locate short remove all components where u find shortted pins

Yes, short is under 2 ohms and continuity to ground.

That has been done in the previous posts but have still been unable to find the main short.

[ktmmotocross]

Re: Alienware 18 LA-9332P 3V, 5V short

there are too many shorts. did u remove pu100 and check?

[khaahk]

Re: Alienware 18 LA-9332P 3V, 5V short

Use lab PSU to find shorts in +3VALW and +3VS, the same with +5VALW and +5VS rails. It is most likely not an easy job - probably need to replace many components (maybe too many). If successful then replace PU100 and PU200, measure mosfets - change if needed, check ram chip for short.

[Johndill]

Re: Alienware 18 LA-9332P 3V, 5V short

there are too many shorts. did u remove pu100 and check?

Yes, PU100 was removed in post#1, however the shorts remained.

Use lab PSU to find shorts in +3VALW and +3VS, the same with +5VALW and +5VS rails. It is most likely not an easy job - probably need to replace many components (maybe too many). If successful then replace PU100 and PU200, measure mosfets - change if needed, check ram chip for short.

I have been looking for a donor board for parts but from what both of you are saying, mine will be better off being the donor board instead, if I can find another AW 18 board to repair.

[Enderhelper]

Had a 5V short on a similar LA board, had to remove around 12 components to get to normal readings on the rail (40k ohms after capacitive spike). Waiting on the chips from Ali rn just hoping the chips I ordered are all good, pretty much wishful thinking. It might be better to just use boards like for this parts.