Laptop problem (Acer Aspire 6920G)

[kostas-]

Hello everybody,

Trying to bring back to life an old laptop and i'll appreciate for any help and advices.

All start when the NEC/TOKIN fail. The laptop was working without reboots when the second core was disabled by the OS. So i decide to replace it. I order one but when i replace it the laptop was showing blank screen.

Next step was to repair it with the smd tantalum capacitors. I wasn't carefull and by accident i put one capacitor wrong with opposite polarity.

After i put correct some other working 2x 470uF caps but the damage was already done from before. I replace the core voltage controller (ADP3208) (from PDF is page 10 - U1002) and two mosfets (Si7686DP) (from PDF is page 10 - Q4&Q6). Still not working.

I'm testing the M/B with only CPU/FAN/memory/MXM card attached only. When i remove the CPU the fan spins at full speed. When i insert the CPU somewhere is a short. The short happens only when a CPU is inserted. I test and other CPU in case the CPU was damaged but happens the same.

From where i should start you think? What have more chances to be damaged with the wrong capacitor polarity?

[Techtiger]

Re: Laptop problem (Acer Aspire 6920G)

check the coil L501 L502 resistance to GND with the CPU & with Out CPU and all Gray Coil of the Mob for voltage, point out which Cap accidently you put wrong opposite polarity

[kostas-]

Re: Laptop problem (Acer Aspire 6920G)

thanks for the response

Without CPU:
L501 = 871Ω
L502 = 871Ω
L15 = 330Ω
L524 = 610Ω
L525 =1480Ω

With CPU:
L501 = 14Ω
L502 = 14Ω
L15 = 330Ω (no change)
L524 = 610Ω (no change)
L525 = 1480Ω (no change)

For Voltage:

Without CPU:
L501 = 0.75V - when power on jumps to 1.6V and increasing to 2.6V
L502 = 0.75V (same as L501)
L15 = 1.84V
L524 = 3.3V
L525 =5.1V

With CPU:
L501 = 0V
L502 = 0V
L15 = 0V
L524 = 3.3V
L525 = 5.1V

The wrong polarity was the tantalum caps under the CPU to replace the NEC/TOKIN. If i am not wrong on PDF on page 16 the C47 (900μF/2.5V).

I did a test and connect the CPU while the M/B was on. The fan didn't stop to spin and stay power on and the coils L501,L502 drop to 0V. Pull it out again the voltage increasing as mention above.

[Techtiger]

Re: Laptop problem (Acer Aspire 6920G)

I don’t see any short in CPU line 14 Ohms is Good, now test C35 36 37 38 39 Cap resistance to ground without CPU, but L501 L502 Voltage increase 2.6 is to high, test those tantalum caps again out of the Mob

[kostas-]

Re: Laptop problem (Acer Aspire 6920G)

A correction: The voltage increase on cpu coils L501,L502 was happening only when the Q5,Q7 mosfets was removed (i remove them to test them out of mob). So i guess was normal that wrong high voltage. Sorry for that, forgot to mention it previous.

So the voltage on L501,L502 is 0.75V without cpu and 0V when i insert it (without power on, just insert it on stand by the voltage drops to 0V).

I guess the caps you mention me is the C535-C539 but they didn't put them on that mob, i guess was optional (pic attached).

I test the two 470μF tantalum caps and looks ok. Those was removed from an other working mob. I test them tho while was on mob. It's a must to test them again out of mob?
If you can't think something else then i'll do it tomorrow.

[Techtiger]

Re: Laptop problem (Acer Aspire 6920G)

In the CPU VRM section you need to match the MOSFET or else they will be unbalanced and Use the same model, and if possible replace both MOSFET , may be you are having a short in CPU socket , they is a way to test it try to buy a CPU socket tester

[kostas-]

Re: Laptop problem (Acer Aspire 6920G)

Yes maybe the short is on socket. I have to test it. I'll find a 478 socket cpu tester. At the very start when remove the faulty NEC/TOKIN and replace it with the new maybe the hot airgun did a damage on the socket joints and for that didn't work at my first repair attemp.

[piernov]

Re: Laptop problem (Acer Aspire 6920G)

You shouldn't use hot air to remove NEC Tokin. It requires a lot of heat and that will damage the socket on the other side.

[kostas-]

Re: Laptop problem (Acer Aspire 6920G)

Yes true. But the hot air was used at start but not too much to do a damage to the socket. At the end removed by destroy it with a tool and iron gun.

I did an optical observation to the socket and didn't find something bad.

I see on the market exists some socket testers but for mPGA478MN it just categorized pins for the address line, control line, standard voltage, Vcc etc

In the PDF file (pga478__p42ghz_512kb_400mhz_fsb.pdf) i guess have the same pin layout with my socket. It's on page 29. It's a good practice to test it with multimeter based on that?

[Aurumnus]

Re: Laptop problem (Acer Aspire 6920G)

Did you managed to fix it?