Dead motherboard

[jultrem]

Hi, I am new here. I have a broken motherborad that I would like to fix. The laptop is an Acer nitro AN515-54. It worked fine until it wouldn't turn on anymore. When the power supply is plugged in, i read 19.58v on the power connector. Then, I followed the current up to a mosfet that I think might be the problem. It is the first mosfet after the power connector so there is no current on almost the entire board. I would like your opinions. In the attached picture, i have 19.58v before the mosfet but nothing after. I tried replacing the mosfet with one that looked the same from an other board but I had no luck so I put back the original. Now I am out of ideas. Thanks in advance for your help !

 

[rjenkinsgb]

It does not look like the big MOSFET has any gate drive? It's most likely a P Channel with the source to the incoming power.

This is a J0315 of another make, which most likely has the same pinout:

https://www.renesas.com/us/en/document/dst/rjj0315dpa-datasheet?r=1341766

If that is the same, then the gate is one of the lower pins that's showing 19V?


It looks like you may be able to download a full schematic here:

Nitro AN515-54 EH50F EH51F Compal LA-H501P Rev.1A Schematic - AliSaler.com

Nitro AN515-54 EH50F,EH51F,EH5VF,EH70F) Compal LA-H501P Rev.1A schematic file download. We are believing in reviving the technology and making minimum

www.alisaler.com

 

[jultrem]

Hi, sorry, it dosent't show in the picture, but the big mosfet does in fact have a gate. It is the pin on the top left and it has no power to it.

 

[Tony Stewart]

That means the switch is fused open, if you by pass that with jumper, you get power thru ( as a test use a current meter ), but something caused that chip to fail from your fault or an internal fault.

... like excessive dust inside and not maintaining it
... or bottom air vents blocked sitting on soft material smothering air flow during >1 hour of battery charging indicated maybe by random shutdowns.

 

[jultrem]

Yeah probably cause I charged it in my bed because it had almost no dust in it and was only a year and a half old when it stopped working. But, when you suggest I jump it, since I don't want to blow up everything, how do you suggest I jump it? Right now, I have power comming in from the drain. When I jump it, should I go from drain to source or from drain to gate? I am not an expert in any means in electronic, I just wan't to fix that laptop and learn a few things. Thank you !

 

[rjenkinsgb]

but the big mosfet does in fact have a gate. It is the pin on the top left and it has no power to it.

A P channel mosfet would be switched on when the gate was low; 0V should = ON
It does appear to be reverse connected though; that is sometimes used for power switching such as that.

 

[Tony Stewart]

I believe this Pch FET is the primary input power switch to feed all the DCDC converters except for maybe the stdby for RTC clock and is enabled from the soft power switch button or slider or disabled from overtemp sensing.

We learn this lesson to ensure free air under the laptop after this experience. I think this was a thermal runaway issue with a bright screen + charger in CC mode + playing high CPU load apps. with no airflow.

A good laptop never runs more than 60'C on CPU full load. Your fan speed on 100% ought to be a clue something is wrong is another clue. Otherwise thermal runaway effects can occur with PTC MOSFETs.

 

[Nigel Goodwin]

We learn this lesson to ensure free air under the laptop after this experience. I think this was a thermal runaway issue with a bright screen + charger in CC mode + playing high CPU load apps. with no airflow.

Good idea, after he mentioned charging it on his bed - it's a very BAD idea, and blocks all the air flow. You always want to charge (or use) a laptop on a hard surface (like a desk) if you can, and if it's actually on your 'lap', then ensure you're not blocking airflow.

 

[jultrem]

Thank you guys for your answers, I did learn my lesson and will not charge my laptop on my bed anymore. Anyways, someone suggested jumping the mosfet a little bit higher in the thread, Is it possible to tell me which pins I should jump. I don't wan't to break anything more than it already is. You can use the numbers in the schema Tony Stewart kindly provided. Thanks !