ACER 5742 Dead M/Board

[John McGivern]

Hi, i am trying to repair this motherboard.
Ny daughter spilled red wine on it.
Adaper 19v
First mosfet PQ51 drain side 19v, nothing on gate or source.

Questions, 1. Do I have to install RAM for testing?
2. Current sense resistor missing R020 -2512-1%.
3. How difficult is it to solder this component?
4. Can I test without this or is value critical?

I have a 30v 1amp variable power supply for testing.

Many thanks in advance.
See photos and PDF.

[Techtiger]

Re: ACER 5742 Dead M/Board

Most probably your 1st Fet is gone since it’s P channel it should cross 19V but less than Drain

[piernov]

Re: ACER 5742 Dead M/Board

Why is the current sense resistor missing?

[John McGivern]

Re: ACER 5742 Dead M/Board

Must have come off when disassembling but never noticed it anywhere.

[piernov]

Re: ACER 5742 Dead M/Board

It looks like it has been removed so wanted confirm. It's required anyway.

[John McGivern]

Re: ACER 5742 Dead M/Board

What is best way to solder this component very tight tolerance 0.5 ml trace gap? Bit vary of shorting traces.

[mcplslg123]

Re: ACER 5742 Dead M/Board

Either with a finetipped solder iron or hot air gun.

[John McGivern]

Re: ACER 5742 Dead M/Board

Thank you mcpisig123.

[piernov]

Re: ACER 5742 Dead M/Board

The current sense resistor is a quite large component. A decent soldering iron and some flux will have no trouble soldering it.

[John McGivern]

Re: ACER 5742 Dead M/Board

Thanks piernov.

[John McGivern]

Re: ACER 5742 Dead M/Board

Should I leave the memory out while testing?

[John McGivern]

Re: ACER 5742 Dead M/Board

Pj15/16/18 all shorted to gnd.

[mcplslg123]

Re: ACER 5742 Dead M/Board

Pj15/16/18 all shorted to gnd.

PJ15/16 are supposed to show very low resistance to gnd.(measure it in resistance mode and not diode mode). thats not a worry for now. PJ18 is your B+ line(19V)-it is shorted. Open the jumper and apply low voltage like 1-2V on the shorted side if you have a bench power supply.

[John McGivern]

Re: ACER 5742 Dead M/Board

Hi, I only have 1 amp will this be enough?

[KvnTM]

Re: ACER 5742 Dead M/Board

Hi, I only have 1 amp will this be enough?

Should be enough to heat up the shorted component. Pour some alcohol on the board and look where it evaporates quickly.

[John McGivern]

Re: ACER 5742 Dead M/Board

KvnTN, thanks for replying, just a novice. I applied 1.8 volts to pj18 side 1 this was on pq62 drain only. R020 is missing so wil have to wait till it arrives to test. Many thanks.

[John McGivern]

Re: ACER 5742 Dead M/Board

Tested all coils diode mode least measurement was 0.024. Hopefully R0.02 will arrive tomorrow. I have first and second mosfets to fit at the same time. Will it be best to remove Ram while testing? Thanks again.

Removed solder from pj18. Pq62 reads1.2v other side of pj18 shorted.

[John McGivern]

Re: ACER 5742 Dead M/Board

Hi Guys, soldered Pr352 this connects to Pj18 which is open. This is side 2 which is shorted to ground. I injected 1volt at side 1 of Pj18 this was on drain of Pq62 nothing on gate/source.
Injected 19v to Pq51 this was on drain/gate/source and also on Pq52 source but nothing on gate/drain. Cheers.

[Techtiger]

Re: ACER 5742 Dead M/Board

your 1st FET is not switching you need PACIN GATE PASS to pin 4 to allow same voltage to cross over there is a body diode in side forward bias PQ51 whatever the voltage on DRAIN it will pass voltage to SOURCE but less than the DRAIN PU18A is the starting point of PACIN unless you don’t have the PASS it will not work

[John McGivern]

Re: ACER 5742 Dead M/Board

Thanks techtiger will change PQ51 tomorrow.