Acer 5742G, PQ88 MOSFET blowing..

[Pauliini]

Laptop stop working. LA-5891P shematic. Missing B+ voltage, reason was that PC326 was shorted. I removed and try again no powerled star and stop quickly. Then I find out that MOSFET PQ 88 and PQ 92 (TPCA8028-H) was broken so I removed both.

After that without CPU and RAM and any other devices laptop start, leds go on charging working. I measured all PJ voltges:

pj23 0,0V
pj6 3,37V
Pj8. 5,1V
pj11. 19,1V
pj14 1,833V
pj7 0,761V
pj2 and pj4. 0,0 V
pj5. 1,518V
pj9 and pj10 0,08V
pj15 and pj16. 0,0V
pj22. 1,5V
pj20. 1,5V
pj18 19,4V

I need some helposti, what Componenta I have to check before replacing MOSFET?
What is reason that MOSFET blowing?

I find another motherboard some MOSFET what of them I can use I have pair of

FDS6676AS

SI7686DP

79NO3S

4634

What about missing +1.0VSPDGPU and +1.05VS_VTTP. Is it all voltges on or not?

I understand that VGA_ON trigger those two missing voltgess after I reassembling laptop
and start again after all Componenta are installed. I also removed battery from mainboard.

Is it possible yhä GPU or CPU is fault. Laptop running quite cool, GPU temp. is running 50-70 degrees.

When I replace MOSFET next, Is it good idea to try first without CPU, RAM and other components and check voltages again before final assembly.

Please help me soon.

[highpulse]

Re: Acer 5742G, PQ88 MOSFET blowing..

well cetainly there many reasons to blow fets , possible cause , capacitors in that section are in short , regulator is pulling high a gate or vice versa making it to bypass to gnd...well many thing can make this happen , but first of all wich board model is it

la-5891p ???? 5742 have 2 type of boards , and bit different from each outher , so give us correct board code for we can help you oout to solve this problem

well cheking online on both schemtic , your must be la5891p , so therefor your cpu controler is the ADP IC

sofirst thing , remove cpu , and access this site , in this moment i cant put attachments , but you can acess schematic here https://cdn.badcaps-static.com/pdfs/...0cbac68b75.pdf

so , remove cpu , and test all mosfet attached to the ADP IC , you can see it on page 54 of the schematic for you can know wich mosfets you need to test , and also capacitor to test to gnd to see if they are in short .

quick way to test mosfet (outisde board)
IF N channel , black probe on drain side (pin 5 6 7 8) and red proble pins 1 2 3 , in this way (on diode mode ) you must have a value showing on your multimeter . now keep black probe on drain side (5 6 7 8) and touch one time with red probe on pin 4 GATE , now if you touch with the red probe again on any pin 1 2 3 it must make NOISE indicating continuity , swap probes black probe 1 2 3 and red probe in any pin of 5 6 7 8 and it must make noise as well showing continuity , then keep red probe on pins 5 6 7 8 , and black probe touch pin 4 gate , and now chek that there is no more continuity .if ok final test , now red probe on pins 5 6 7 8 , and black probe on pin 1 , and it must display on multimeter infinite or else (1).

for P channel , its the oposite , gate is activated with black probe instead of red probe
test all fets , if all ok , good ,
chek on schematic main capacitors for main cores lines , test them like this , black probe attached to any ground spot , like USB shield or holes . red probe , touch negatice side of mosfet it will make continuity , the outher side of the fet CANNOT make continuity ,if it does , means it is shorted .

any doubt's just ask , and we will go further with the repair , first test fets and capacitors
cheers

[Pauliini]

Re: Acer 5742G, PQ88 MOSFET blowing..

well cetainly there many reasons to blow fets , possible cause , capacitors in that section are in short , regulator is pulling high a gate or vice versa making it to bypass to gnd...well many thing can make this happen , but first of all wich board model is it

la-5891p ???? 5742 have 2 type of boards , and bit different from each outher , so give us correct board code for we can help you oout to solve this problem

well cheking online on both schemtic , your must be la5891p , so therefor your cpu controler is the ADP IC

sofirst thing , remove cpu , and access this site , in this moment i cant put attachments , but you can acess schematic here https://cdn.badcaps-static.com/pdfs/...0cbac68b75.pdf

so , remove cpu , and test all mosfet attached to the ADP IC , you can see it on page 54 of the schematic for you can know wich mosfets you need to test , and also capacitor to test to gnd to see if they are in short .

quick way to test mosfet (outisde board)
IF N channel , black probe on drain side (pin 5 6 7 8) and red proble pins 1 2 3 , in this way (on diode mode ) you must have a value showing on your multimeter . now keep black probe on drain side (5 6 7 8) and touch one time with red probe on pin 4 GATE , now if you touch with the red probe again on any pin 1 2 3 it must make NOISE indicating continuity , swap probes black probe 1 2 3 and red probe in any pin of 5 6 7 8 and it must make noise as well showing continuity , then keep red probe on pins 5 6 7 8 , and black probe touch pin 4 gate , and now chek that there is no more continuity .if ok final test , now red probe on pins 5 6 7 8 , and black probe on pin 1 , and it must display on multimeter infinite or else (1).

for P channel , its the oposite , gate is activated with black probe instead of red probe
test all fets , if all ok , good ,
chek on schematic main capacitors for main cores lines , test them like this , black probe attached to any ground spot , like USB shield or holes . red probe , touch negatice side of mosfet it will make continuity , the outher side of the fet CANNOT make continuity ,if it does , means it is shorted .

any doubt's just ask , and we will go further with the repair , first test fets and capacitors
cheers

Hello!

Thanks for your quick replay

This is all information my laptop

CPU is Intel Core i3-380M @ 2.53GHz There is Intel chipset and GPU is ATI RADEON HD6370M 512MB.

Motherboard model is

NEW70 LA-5891P
Rev.1.0
2010-03-23

Bottomside my laptop is marking:

Aspire 5742 Series
Model NO. PEW71

Aspire 5742G-384G50Mnkk

SNID: 04734305516
S/N:LXR8Z0200804753C0F1601


http://aijaa.com/y3IXJG

http://aijaa.com/n3PHr7

[highpulse]

Re: Acer 5742G, PQ88 MOSFET blowing..

ok , so start making the measurement i requested to you for we can solve the short you got

[Pauliini]

Re: Acer 5742G, PQ88 MOSFET blowing..

ok , so start making the measurement i requested to you for we can solve the short you got

I remove CPU, RAM and all other components and check all Mosfets near to ADP IC by Fluke 87 True RMS meter. I also measured all ADP 48 pins resistance to ground with and without CPU installed.

I am not sure, how to measure Mosfet on the Mainboard. Resistane to ground and clear shortcircuit is quite easy to see, but turning Mosfet on and off is not.

I learning to check one big tree pin Mosfet by your info and it works. I cannot still check sameway 8 pins Mosfet, why?

Near ADP is 4 Mosfet, bottom side has PQ87 and PQ90, PQ86 and PQ91 is not installed. Topside has PQ88 and PQ92. PQ89 and PQ93 are not installed. As I say before PQ88 and PQ92 are 100% sure broken so I remove them before any measurement. SO topside near to CPU socket has not any Mosfet, only two working i hope are bottomside.

Measured resistances pins to Ground, CPU not installed

PQ87

1,2,3: 0,5 ohm
4: 202,5 kohm
5,6,7,8: 680 kohm

PQ90

1,2,3: 0,5 ohm
4: 203,8 kohm
5,6,7,8: 680 kohm

PQ88, no IC

1,2,3: 0,5 ohm
4: 4,92 Megaohm
5,6,7,8: 0,5 ohm

PQ92, no IC

1,2,3: 0,5 ohm
4: 0,5 ohm???
5,6,7,8: 0,5 ohm

ADP3212, CPU not installed

1: >Mohm
2: 93,kohm
3: 5,6kohm
4: 23,2 kohm
5: 100 ohm
6: 1,75 kohm
7: 6,1 Mohm
8: 5,1 kohm
9: 5,0 ohm
10: 5,6 Mohm
11: 6,7 kohm
12: 0,5 ohm
13: 80,6 kohm
14: 69,3 kohm
15: 162,1 kohm
16: 550..850 kohm, not stable
17: 271,4 kohm
18: 8,5 ohm
19: 65,0 kohm
20: 271,4 kohm
21: 273,5 kohm
22: 5,72 Mohm
23: 5,72 Mohm
24: 6,92 Mohm
25: 203 kohm
26: 0,5 ohm
27: 0,5 ohm
28: 0,5 ohm
29: 0,5 ohm
30: 0,5 ohm
31: 4,8 ohm
32: 10,0 ohm
33: 0,5 ohm
34: 1.0 ohm
35: 201,1 kohm
36: 12,3 Mohm
37: 0,5 ohm
38: 0,5 ohm
39: 0,5 ohm
40: 600 ohm
41: 600 ohm
42....48: 1.0 kohm

[Pauliini]

Re: Acer 5742G, PQ88 MOSFET blowing..

No lucky, ADP3212 IC is very hot now and it is possible to change. Thanks anyway, I give up to try fixing this mobo..

[shutt1e]

Re: Acer 5742G, PQ88 MOSFET blowing..

hi, cannot make new posts yet, so sorry if i use yours. i have a power off issue with this board, i'm pretty sure it is not cpu overheating.
even on a cold start it stay on 10/20 seconds then power off, no components on board seem to overheat, and it power off randomly, after 20 seconds, or even 10 minutes. pressing powerbutton it restart normally then power off again.
i have many broken spare boards of this kind (new70) where i can pull components. any suggestion on what i can try first?