la-c582p blown transistor

[mawa1105]

I found a blown transistor (q24) in the picture. I replaced it, and it blew again 🤔
If I measure the Voltage while turned on without the transistor on the pads, it is 10V, 3.3V, 0V The resistance if turned on: High, High, 0.
Anny idea how I could proceed?

Regards
Mawa

[mon2]

Hi.

1) never measure resistance with the power on.

2) what is the part number of the original component? Which part was applied as the replacement?

3) do make a note of the pin #1 dot on the top surface of this part. Most likely the part polarized.

[mawa1105]

Hi,
Resistance with power off:
5 MOhm, 55 KOhm, 0,2ohm.
The part is supersmall but As far as I can read on a similar looking one on the other side its F28 (Picture attatched)
Pin 1 is marked in another picture.

Thanks in advance
Mawa

[mon2]

From the LA-C581P schematic, Q24 = TPCF8002. There is a polarity to the component so be 100% the replacement is aligned in the same orientation as the original. Part should be inexpensive so do order some spares and test again.

Q24 = TPCF8002

reference:

TPCF8002 N Channel MOS 30V 7A SOT23-8 MARKING F2B Low drain-source ON resistance Low leakage current|Welcome to Eric Online Store - Shenzhen ERIC Electronics Co., Ltd. (eric1688.com)


Tpcf8002 Printing F:2b F28 F2b Sot23-8 - Contactors - AliExpress


Datasheet is attached.

[mawa1105]

Hey,
I tried it again, with a desoldered part from another board. Same phenomenon. Its blowing imedeately and the Fan starts spinning continously.
Maybe there is sth. wrong with the "Think-Engine"? The IC U101, thats controlling this little Mosfet?

Also Im struggling to find where VCC3M and VCC3B is comming from?! Could you tell me on which page in the Datasheet it is listed?

Thanks for your awesome support.

[mon2]

Suspecting that you have an excessive loading condition on VCC3B which is causing this mosfet to burn out.

Remove all power -> meter in resistance mode -> measure the resistance to ground of VCC3B. Perhaps a good idea to flux and carefully remove this now defective mosfet out of the circuit before you make the resistance measurement.

Will post the source of this switched power rail in a sec from the other similar board schematic. In summary, this mosfet is acting like a solid state relay to power the downstream rail of VCC3B ON / OFF. When it is ON, the load is too much and burns out this part.


VCC3M = power rail producer.
VCC3B = power rail consumer.

[mawa1105]

EDIT: I mixed the readings between working and broken😣

Okay,
on the broken board, that I need to run once again:
between Pin 5 and GND we have 0,3Ohm
between Pin 4 and GND 8,45KOhm
between Pins 123678 and Pin 4 10k (rising)
between Pins 123678 and Pin 5 440Ohm /Reversed Polarity: 500k

on the initial not broken board:
between Pin 5 and GND we have 2k (rising)
between Pin 4 and GND 11,65kOhm
between Pins 123678 and Pin 4 10k (rising)
between Pins 123678 and Pin 5 3kOhm (rising)

Could c19 be broken? And how can I identify "Cs" there is no writing on the silkscrenn.

Thanks so far.
I have the feeling it might boot up sometime again...

[mon2]

Is it possible that the readings are reversed from the good to the bad part?

pin #5 to ground are the measurements of interest.

if a low resistance = heavier load = burning out this mosfet.

[mon2]

Ok - now the readings are making sense. Pin #5 resistance is the root cause of the mosfet damage.

Do you have any connected cables to the main logic board? If yes, remove each and check if the pin #5 resistance increases.

Would you have an adjustable power supply for voltage injection? Often can be used to heat up the shorted part on the board.

[mawa1105]

Jeah... Sorry, mixed the readings..

when I apply a voltage from my laboratory power supply, ther is a current of 3A at 3V immediately flowing. But nothing is getting noticably hotter...

How can I find the the short circuit?

[mawa1105]

There is nothing connected to the board. Not even the Wifi-card

[mon2]

Are you applying this voltage from your external power supply onto pin # 5 where there is the low resistance? If yes, someone is heating up and this part must be located. Apply IPA (Costco pharmacy alcohol is great) onto the board and then perform this voltage injection. The area where the IPA evaporates fastest due to the heating process is the guilty component.