Acer Aspire E1-571 (Q5WV1 LA-7912A) many fets defect, why?

[G33RT]

Hi to all,

I have a strage defective laptop mainboard.
It's an Acer Aspire E1-571
The board vendor: HannStar
Q5WV1 LA-7912A
Rev: 2.0
2012-08-24

The laptop sudden would not start anymore no respond and no LEDs whatsoever.
I discovered that the PSU was gone defective due to a short in the DC-Plug input, as the dc-plug and inside connector where okay I looked further thr circuit.

As I measure the input FET and Caps I soon saw that PQ9 was shorted what is comon whit these boards normaly due to shorted cap(s).

There are no brun components nor PCB tracks!

At the moment I gave up on trying to repair as I now discovered so many many FET's are shorted.


List of shorted FET's:

PQ9 AO4304
Although PQ10 & PQ11 are just fine !

PQ29 FDMC7696 shematic page 50
PQ30 AO6504 shematic page 50

PQ35 FDMC7696 shematic page 52
PQ36 AO6504 shematic page 52
PQ37 FDMC7696 shematic page 52
PQ38 FDMC7696 shematic page 52
PQ39 AO6504 shematic page 52
PQ40 AO6504 shematic page 52

If I go any further with repairing I need to know at least what the heck is going on here and if one of you guys have experience similar defects like these?

Thanks in advance for your reaction!

[caspian]

Re: Acer Aspire E1-571 (Q5WV1 LA-7912A) many fets defect, why?

which pins of the FETs are shorted?
are they shorted to each other or shorted to ground?
have you tested them separated from the circuit?
do you see any corrosion on their pins?

[caspian]

Re: Acer Aspire E1-571 (Q5WV1 LA-7912A) many fets defect, why?

multiple damages are usually caused by liquid spill.

[G33RT]

Re: Acer Aspire E1-571 (Q5WV1 LA-7912A) many fets defect, why?

I measure the FET's from Source-to-Drain and Drain-to-Source.

No liquid (ever) was spilled on the device.

A lightning strike could be, but not likely :-)

It's a real mistery.

[caspian]

Re: Acer Aspire E1-571 (Q5WV1 LA-7912A) many fets defect, why?

a FET has the duty to short its Source and Drain when it gets specific input voltages at its Gate.
that is normal.

I measured a FET a while ago which had a short from its Gate to Drain only when it got powered. without power, it had no short from its Gate to Drain. this is abnormal and I never discovered its cause.

[caspian]

Re: Acer Aspire E1-571 (Q5WV1 LA-7912A) many fets defect, why?

It will be great if technicians share their experience about shorted transistors in computer boards.

[G33RT]

Re: Acer Aspire E1-571 (Q5WV1 LA-7912A) many fets defect, why?

All mosfets are tested off-board with a transitor/mosfet tester.
As I already menstion they are all defect.
Anyone have a clue what could happend?

[caspian]

Re: Acer Aspire E1-571 (Q5WV1 LA-7912A) many fets defect, why?

I think you meant a permanent short from Source-to-Drain.
Yes, that is a common fault in MOSFETs.
and your question is: How did multiple MOSFETs become shorted at the same time?
It will be great if technicians share their experiences.

[G33RT]

Re: Acer Aspire E1-571 (Q5WV1 LA-7912A) many fets defect, why?

Yes, that is so strange to me, you can heva some bad fet's and cap's that lead to shorts etc...
But what the heck ish happend here, no liquide is spilled on the device and curefull threated.
So why are there so many defective fet's?
A normal awnser would be a chain reaction cause multiple overloads that lead to shorts but if you look the schematic this is not the case !?

[caspian]

Re: Acer Aspire E1-571 (Q5WV1 LA-7912A) many fets defect, why?

what is common between those shorted transistors is that they are all connected to the B+/Vin line.
you have to check the resistors and the capacitors which are connected to the B+ line.
and see if they are faulty or not.
if they are mostly faulty, you will find out what happened.