Troubleshooting: Lenovo Motherboard

[DanFen]

Hi, I have a Lenovo motherboard that's not powering on. It's a Lenovo G40-30 ACLU9/ACLU0 NM-A311 Rev 1.0

I didn't manage to find the schematics for this revision, but found one for Rev 0.2... and I'm attaching this even though it's already uploaded in this forum.

Please note that I am quite a newbie in the sector, so I'm trying to trace the voltages component by component... starting with DCIN and moving forward.

19V at DCIN is fine. It reached PQ301 mosfet. Then there is another mosfet (PQ302 on the schematics, and noticed that it outputs 1.045V. And at this stage I was lost, cause I can't understand why it would do this, and not even sure if it supposed to do this at all. This tells me that every other component from now onwards is getting this low 1.045V. Is my thinking correct? In fact, even the battery connector is getting such voltage.

Would appreciate if you can guide me in the right direction to troubleshoot this Thank you

Dan

[kiraro]

Re: Troubleshooting: Lenovo Motherboard

what is the voltage measurement of the p-channel PQ302 ( source (pin1),gate (pin4), drain (pin 5) ), and PU301 :BQ24737RGRR, vcc(pin20), ACDET (pin6), ACOK (pin5).

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Hey So...

PQ302
S: 19V
G: 19V
D: 1.04V

PU301
This number on the IC is BQ737 TI. I am not sure if this is the same as the one in the schematic. The number 16 on the right hand side confused me even more, cause the datasheet shows 16 top right. So I hope I got the pinouts correctly!
VCC: 0V
ACDET: 2.57V
ACOK: 0V

Because I'm unsure, I'm attaching a photo. Thanks

what is the voltage measurement of the p-channel PQ302 ( source (pin1),gate (pin4), drain (pin 5) ), and PU301 :BQ24737RGRR, vcc(pin20), ACDET (pin6), ACOK (pin5).

[piernov]

Re: Troubleshooting: Lenovo Motherboard

Check PQ301 for short between drain/source/gate.

As you can see on the picture, the chip is rotated 90° right. Pin 1 is top-right, with the dot on the chip and the white line on the board. Pins are counted counterclockwise. Numbers on the board in the corner of the chip gives you pin number at this position.

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Can I test PQ301 in circuit or do I have to remove from the board? Just to be sure, you are referring to PQ301 and not PQ302 right?

Thanks for the explanation about the IC. I was following the schematics as shown thinking the pins match exactly how it's drawn!

So these are the correct measurements for PU301:

VCC: 19V
ACDET: 2.57V
ACOK: 0V

Check PQ301 for short between drain/source/gate.

As you can see on the picture, the chip is rotated 90° right. Pin 1 is top-right, with the dot on the chip and the white line on the board. Pins are counted counterclockwise. Numbers on the board in the corner of the chip gives you pin number at this position.

[piernov]

Re: Troubleshooting: Lenovo Motherboard

PQ301 indeed, test in-circuit.

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

OK thanks. So I tested using this method, hope it's a correct one.

Drain pins: got continuity between all

Then I held the positive lead onto the Gate and moved the positive onto each of the Source pins. There was no continuity (no beeps on the MM).

[kiraro]

Re: Troubleshooting: Lenovo Motherboard

OK thanks. So I tested using this method, hope it's a correct one.

Drain pins: got continuity between all

Then I held the positive lead onto the Gate and moved the positive onto each of the Source pins. There was no continuity (no beeps on the MM).

Drain pins (pin 5-6-7-8) they are internally connected together by default,
source pints (pin 1-2-3) together also ,
gate (pin4)

it's a p-channel so by default when you held the positive probe (red) onto Drain ,and the black probe onto source you should get between 0.500.. 0.600 in normal condition, and when you inverse probes it's open.

For P-Channel:

Short the gate and drain pins of the P-mosfet. This will initially enable the internal capacitance of the device to discharge (which is essential for the testing process) touch the RED probe to source and the BLACK probe to drain of the mosfet, you will find an "open" circuit reading on the meter.
Next, without moving the RED probe from the source, remove the black probe from drain and touch it to the gate of the mosfet for a second, and bring it back to the drain of the mosfet, this time the meter will show a continuity or a low value on the meter.this will confirm your mosfet is alright.

For N-Channel:

Short the gate and drain pins of the mosfet. This will initially keep the internal capacitance of the device completely discharged, touch the black probe to source and the red probe to drain of the transistor, you should see an "open" circuit indication on the meter.
Now keeping the black probe touched to the source, lift the red probe from drain and touch it to the gate of the mosfet momentarily, and bring it back to the drain of the mosfet.This time the meter will show a continuity or low value.this will confirm your mosfet is alright.

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

That explains it Positive on Drain and Negative on Source gave a reading of 536 k ohms

As regards to the test, I've shorted the gate and drain using the tweezers and went ahead with the instructions. At the end, the meter never showed continuity. It stayed 0L with no beep.

[kiraro]

Re: Troubleshooting: Lenovo Motherboard

Check if there is a short on B+, resistance to ground on PR301.

[piernov]

Re: Troubleshooting: Lenovo Motherboard

It's in-circuit so the testing method above won't work. It doesn't really matter as the point was just to check if drain/source/gate were permanently shorted together (MOSFET melted).

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Hi piernov, so what would be the correct way to test it in circuit? Was my approach bad? If it's more accurate I can just remove it, test it, and put it back.

It's in-circuit so the testing method above won't work. It doesn't really matter as the point was just to check if drain/source/gate were permanently shorted together (MOSFET melted).

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

So what I have so far is:

PQ302 gets 19V on Source but only outputs 1.04 on Drain.

Testing the same mosfet PQ302 in diode mode (-ve on Pin 2 and +ve on Pin 7) gets no results, in circuit. PQ301 returns ~560. Because I have no mosfet to replace with (I'd need to order), I wonder if it's clear that the problem is the mosfet, or if it can also be some other component on the same circuit?

I'm attaching a screenshot of the schematic to make it easier.

[piernov]

Re: Troubleshooting: Lenovo Motherboard

https://www.badcaps.net/forum/showpo...3&postcount=10

[Techtiger]

Re: Troubleshooting: Lenovo Motherboard

What voltage you get in PACIN ?

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Not sure how to do that, would need some assistance

https://www.badcaps.net/forum/showpo...3&postcount=10

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Looked for PR311, but couldn't find it, so I checked for PQ306B (and I am guessing that PQ306 is both PQ306A and PQ306B in the same mosfet).

Checked voltage on this mosfet and only got the following voltages:

Pin 1: 0V
Pin 2: 0V
Pin 3: 19V
Pin 4: 0V
Pin 5: 0V
Pin 6: 7.3V

Datasheet

What voltage you get in PACIN ?

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Some more closeups to make things easier:

[Techtiger]

Re: Troubleshooting: Lenovo Motherboard

pin 5 should get 3.3V through PR311 for this to work you need PU301 pin 16 REGN 6V test this point what voltage BQ24737 ? do you have a DC power LAB ? remove PQ302 test it out of the MB in DIODE mode dont put it back for the moment

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

REGN confirmed 6V. I don't have a DC Power Lab. Tempted to get one, only if I get better with this

... I'll get PQ302 out.

pin 5 should get 3.3V through PR311 for this to work you need PU301 pin 16 REGN 6V test this point what voltage BQ24737 ?