Msi GT72 - MS-17851 V1 board no power

[mikay786]

Trying to figure out why I have no power on this board.

I’ve got power coming in from original charger fine, 1st 2nd mosfets seem fine.

I’ve got no voltages on the bios chip on any of the pins including the vcc

I’ve got 3.3v on the power button connector and does drop to 0 when pressed

I’ve noticed at a pair of mosfets I have got 19v at drain but nothing on the opposite end so kind of thinking I have a issue here

The mosfet after that has 100ohm resistance between drain and source.

Just wanted to make sure I’m on the right track and anything else to check

[mon2]

Re: Msi GT72 - MS-17851 V1 board no power

Yes, you are.

Link the schematic if available in the schematic forum.

The mosfets you are referencing are likely the usual DCin mosfets. Which charger IC is nearby? Perhaps the BQ series? Share the topside markings of the same.

If yes, measure the voltage to ground of each pin on this mosfet. If N-channel mosfets, gate should be ~25 volts to enable.

Update - never mind - found the schematic in my paid database.

The charger IC is indeed BQ series but the ACDRV pin is not used. Instead, your DCin*2 mosfets are P-channel.

So gate pin must be LOWER than the source / drain pin voltage to enable.

The low resistance you have observed is not a good sign is often means the mosfet is leaky.

See attached for the partial schematic of this region.

Proceed to measure the source / drain / gate pin voltage to ground of each of these DCin mosfets.

Post each measurement.

[mikay786]

Re: Msi GT72 - MS-17851 V1 board no power

The low resistance was on the mosfet near the ram with the red arrow.

PQ1

• G - 9.78
• S - 19.75
• D - 19.75
• RESISTANCE S & D is 15 MEGA OHMS

PQ2

• G - 8.31
• S - 19.75
• D - 19.75
• RESISTANCE S & D 32 KILO OHMS

PQ7

• G - 0
• S - 0
• D - 19.75
• RESISTANCE S & D 14 KILO OHMS

PQ8

• G - 0
• S - 0
• D - 0
• RESISTANCE S & D 100 OHMS

[mon2]

Re: Msi GT72 - MS-17851 V1 board no power

PQ2 is showing a very low resistance across source & drain.

Suggest to flux it and carefully remove this mosfet and then check it's resistance again once it is cool and on your work table.

[mikay786]

Re: Msi GT72 - MS-17851 V1 board no power

removed all 4 mofset

pq1&2

red probe drain / black on source both read about 5.6 M ohm
and 0.l when i flip the probes, why is this?

pq7

black prove drain red on source = 8.5 m ohm
0.l when probes reversed

pq8

black prove drain red on source = 6.3 m ohm
0.l when probes reversed


on the empty pads board

pq2
red probe drain / black on source read about 0.47 M ohm
reversed 0.47 m ohm and climbing slowly

pq1
red probe drain / black on source weird reading jumping 0.l & 2.6 k ohm on off
reversed 76 k ohm

[mikay786]

Re: Msi GT72 - MS-17851 V1 board no power

Do the mosfet reading look normal?

And the board readings where the mosfets were?

[mon2]

Re: Msi GT72 - MS-17851 V1 board no power

PQ1 measurements do not.

[mikay786]

Re: Msi GT72 - MS-17851 V1 board no power

Possibly another component like a capacitor nearby causing issues?