[FIXED!] Need Help: Acer 8930 le2 laptop keeps restarting after a few seconds

[Watth]

Edit: Fixed! see solution here  by user xavier60

Hey there,
A neighbour asked me to have a look at his Acer 8930G series laptop (model 8930G-844G32Bn). The laptop is still useful, and they'd like to be able to recover some files from the PC's HDD.
Initially the problem was that it didn't charge : removing one screw revealed the problem was the wire to the PSU connector was broken (stupide design idea : the barrel connector twists when the laptop screen is opened). It looks like a common failure un this model. I fixed the wire, the laptop is now powered.

Now the problem is that the laptop won't stay on for more than a few dozen seconds. Since the first try, it turned on, Windows started its repair process thing, and the PC would restart.
I checked the BIOS, set thing to default, removed the battery, and tried again : same thing, the laptop keeps restarting after a few dozen seconds (sometimes before).
I then tried with a live Ubunbtu USB drive, even after disconnecting the HDD, same thing.
I removed every thing I could (USB ports PCB, PCI slot, Optical disk drive, WiFi module, etc.) and the only thing remaining were the screen, the power button, the keyboard and the power adapter. I checked with either RAM modules. Same thing. The copper heat pipe is not that hot : I can keep my finger on it, so I guess it's under around 55°C. Still I replaced the thermal paste.
A weird thing : If I open the BIOS menu, it doesn't restart on its own.

TLDR: laptop restarts after a few dozen seconds on its own.

What could be the problem? What should I check?
Thanks!

[Rasz]

Graphics Processor NVIDIA GeForce 9600M GT

Start windows in safe mode, this wont load gpu driver

[xavier60]

The model seems to use the troublesome NEC Tokin capacitor that filters the Vcore supply.
Search for " Acer 8930G  NEC Tokin"

[Watth]

That could really be it. I'll definitely try to replace this.
To be continued...

[Watth]

Well that was indeed the problem. I could fix the computer for 8.48€ of capacitors.
Thanks a lot!

[lacta13]

Hi folks. i have the same problem with my acer aspire 8930G,my laptop keeps restarting while booting,even if i boot from a cd.
cause 2 people here said 2 solution,one soft and one hard, i tryed the soft one to boot in safe mode and indeed it booted fine. so cause it booted in safe mode,means it is the nvidia graphics cards faults?and what is the solution to that?also means it is not the tokin chip problem that another user said?

[Rasz]

Tokin cap seems to be the default go to answer for those laptops when they start failing to boot, so replace it first

[xavier60]

The popular replacement is 4x  330uF low ESR tantalum caps.
Near to 10 years later, they are also failing.
I also used 10x 100uF MLCCs in some which are still fine.

[lacta13]

so you don't propose to use same NEC capacitor,right?cause i also found that here

so i found here in Greece this type,is that correct?

https://www.markidis.gr/en/capacitor-tantalum-low-esr-330uf-63vdc-case-e-2917-tps-smd

Manufacturer AVX
Type of capacitor tantalum
Kind of capacitor low ESR
Capacitance 330΅F
Operating voltage 6.3V DC
Case E
Case - inch 2917
Case - mm 7343
ESR value 100mO
Capacitors series TPS
Mounting SMD
Tolerance ±10%
Operating temperature -55...125°C
Capacitors features low ESR resistance value

or this one?

https://www.aliexpress.com/i/32822778493.html

[xavier60]

No, the NEC Tokin capacitor was failing after 4 years in the Toshiba Satellite A200 laptops. It can't be hand soldered anyway.
It was a long time ago and I can't remember all of the details. They were Panasonic tantalums, the ESR might have been lower.
I will only use MLCCs now. They are 100uF 6V that I got on Aliexpress years ago.
With the MLCCs I fitted recently, I used Mechanic brand 138°C solder to make soldering easier.