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Old 05-25-2022, 06:47 AM   #1
lapfix
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Default Acer 5741 LA-5892p not power on.

Hello friends , thinking was easy to fix...but

Got this Acer 5741 5742 LA-5892p that didn't power on.

When charger is plugged ,got only 7v at PR351 = P3..the 2 first mosfet are ok but i got 18.7v at the 2 gate...it's P-channel so must be 8-10v..
To get the right gate voltage Pq63 must be ON to allow the rule of voltage divider..but it's off = PQ63 pin1 =18v.

PACIN = 3v and same at first pin of PR371...but 0v at pin 2.
If i got 3v at side 2 of R371 so PQ 59/PQ 63 will be ON and the voltage divider will be ok...but no 3v.

Testing PQ 56/ PQ 58 / PQ 59 /Pq 63 for short and they are all OK.

Testing PU17 : no voltage at DCIN pin 24...no voltage at the enable pin

To get DCIN PQ 55 must be ON than the gate of PQ 54 will be realize fron the voltage divider and the voltage pass from P3 to DCIN...but it's off.

PQ 55 is off because no FSTCHG ( who supply the enable pin too of pu17 )

So..direction 3/5 v always....no short and no voltages!!..so the io is not supllied...so no FSTCHG.

Changing pu16 still the same.

I m so confused here..any others ideas
Thank you
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Old 05-25-2022, 07:05 AM   #2
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Default Re: Acer 5741 LA-5892p not power on.

Good review so far !

There is another similar case on the thread and following the same logic flow.

What is the voltage of ACOFF ?

ACOFF is driving the base of PQ65 to turn it ON and this is causing the resistor, PR371, pin # 2 to be 0v.

This will then turn OFF PQ63 so the voltage divider is not enabled.

Can you confirm this ?
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Old 05-25-2022, 07:20 AM   #3
lapfix
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Default Re: Acer 5741 LA-5892p not power on.

Thank you mon2...yes i read all the threads post it here to know more...and i read also yours.

Yes i know for your logic about PQ65...so pin 2 = ACOFF is 0v ...i doubt like you maybe he's shorting and causing this issue...so i desoldered and see if i got 3v at pin2 of PR371....but nothing.

Pr 371 :
side 1 =3v
side 2 = 287mv...that's what i find at PQ65 pin1 and also PQ 59/ 63 gate

PR371 = 22K ...when i desoldered Pq 65/59/63 i find this value...so i think that the resister is ok
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Old 05-25-2022, 07:47 AM   #4
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Default Re: Acer 5741 LA-5892p not power on.

What is the voltage of Pin # 1 of PD15 dual diode ?
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Old 05-25-2022, 07:51 AM   #5
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Default Re: Acer 5741 LA-5892p not power on.

26mv...tested with diode mode pd is ok
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Old 05-25-2022, 08:43 AM   #6
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Default Re: Acer 5741 LA-5892p not power on.

Can you confirm in diode mode that the component is not defective?

Do check also 2 & 1 then reverse the meter leads, etc.

Concern is if ACON is being pulled down due to this diode.
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Old 05-25-2022, 08:58 AM   #7
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Default Re: Acer 5741 LA-5892p not power on.

yes i confirm
0.325 reading for 2 to 1 and 3 to 1 , 0l at reverse
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Old 05-25-2022, 09:01 AM   #8
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Default Re: Acer 5741 LA-5892p not power on.

Remove PD15 and then check the voltage of ACON.

What is the voltage of RTCBATT ?
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Old 05-25-2022, 11:03 PM   #9
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Default Re: Acer 5741 LA-5892p not power on.

Remove PQ56/58 and test gate voltage on PQ51 again.
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Old 05-26-2022, 06:16 AM   #10
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Default Re: Acer 5741 LA-5892p not power on.

Hello again and sorry to be late....and the lap is solved

RTCBATT = D1 = 2.7v
Without PD 15 i got this voltages at the place of pin :
1 = 5.22v
2 = 4.62v
3 = 3.125v

Removing pq56/58 sitll the same issue.

After removing PD15 i got a short to GND !! don't know how...i find the short at PQ73..i notice that he got a little corrision...so replace this mosfet

and replace PD15 and the voltage still there...but always 18.5v at the gate of 2 firsts mosfets...back to PR371 and i find 3v at the 2 sides!!! so PQ 63/59 are ON now but still 18.5v at the gate...test again the 2 first mosfet find that PQ 52 is shorted now...replaced and all is OK..8.05v at the 2 gate..the lab is ON.

Maybe PQ73 was faulty at first and when he s totally short and repalced the issue is Gone.


Thank you my friends mon2 and mcplslg123
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