Troubleshooting: Lenovo Motherboard

[Techtiger]

Re: Troubleshooting: Lenovo Motherboard

Trace back this Curcit write down all voltages pic and upload,
P-Channel Fet black probe to S Red probe to D you should get value of 50-600 if you reverse probe no value or high value , S black Probe G Red probe no value or high value, D to G no Value or high val

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

REGN confirmed 6V. Followed the below in Diode mode:

1. 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.
.... got 0L

2. 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.
... got a very low value ~0.002

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

[kiraro]

Re: Troubleshooting: Lenovo Motherboard

meter in resistance mode , black probe to ground red probe to PR301 ,what value you get ?

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Is it OK to give power without the mosfet?

Following your instructions on the removed mosfet:

1. Black on Source and Red on Drain: 0.517
2. Reverse: 0L
3. Black on Source and Red on Gate: 0L
4. Drain to Gate: 0L

Trace back this Curcit write down all voltages pic and upload,
P-Channel Fet black probe to S Red probe to D you should get value of 50-600 if you reverse probe no value or high value , S black Probe G Red probe no value or high value, D to G no Value or high val

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

2.87, but mosfet PQ302 is currently removed from circuit (if that matters). Removed it for the testing techtiger is suggesting.

meter in resistance mode , black probe to ground red probe to PR301 ,what value you get ?

[kiraro]

Re: Troubleshooting: Lenovo Motherboard

2.87, but mosfet PQ302 is currently removed from circuit (if that matters). Removed it for the testing techtiger is suggesting.

you mean 2.87 ohm?or kilohm or Megaohm?,So if it's 2.87 ohm that mean you have short un B+ line in the motherboard, and you should solve this short by finding what component cause the short ,or bad capacitor, a little trick you can measure the resistance between the PR301 and others coils in motherboard if you find a very low value with one of them, than check upper transistor in this power section ,if nothing so probably bad capacitor , I give you this trick because you don't have power lab.

[Techtiger]

Re: Troubleshooting: Lenovo Motherboard

Is it OK to give power without the mosfet?

Following your instructions on the removed mosfet:

1. Black on Source and Red on Drain: 0.517
2. Reverse: 0L
3. Black on Source and Red on Gate: 0L
4. Drain to Gate: 0L

PQ302 is good now check the voltage on drain side of the mosfet PQ302 on MB with out the mosfet, after check out the post 21# follow the Curcit write down all voltages pic

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Thanks for the help. It was Megaohm. What is strange now, is that everytime I check it I get a value and it starts decreasing slowly. It's actually never the same, sometimes it increases, sometimes it stays the same but it's always a different value. What does this mean?

you mean 2.87 ohm?or kilohm or Megaohm?,So if it's 2.87 ohm that mean you have short un B+ line in the motherboard, and you should solve this short by finding what component cause the short ,or bad capacitor, a little trick you can measure the resistance between the PR301 and others coils in motherboard if you find a very low value with one of them, than check upper transistor in this power section ,if nothing so probably bad capacitor , I give you this trick because you don't have power lab.

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

It's difficult to follow the tracks with a handheld magnifier maybe I should also get myself an entry level scope (any recommendations?)!

However, anything around PQ309 is 0V.

In this case, I think it's more accurate if I post an actual photo with the voltage measurements rather than guessing which resistors on the schematic are located. Tried to zoom as much as I can.

PQ302 is good now check the voltage on drain side of the mosfet PQ302 on MB with out the mosfet, after check out the post 21# follow the Curcit write down all voltages pic

[peste]

Re: Troubleshooting: Lenovo Motherboard

put PQ 302 back and remove PR301 from the motherboard and measure the voltage where you now have 1.04v.

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

EDIT: I see you have asked for PR301 to be removed
EDIT 2: With PR301 out situation is still the same, it's actually now below 1V. Below info is with PQ301 out, due to mistake, but readings in the photo remain the same with PR301 out.

With PQ301 out and PQ302 in place, there is now no voltage on PQ302 (just a 0.2V).

Is it possible that the DRAIN pads of PQ301 has 19V and the SOURCE pads have none? If you look at post #29, DRAIN pads would be the ones on the right.

With PQ301 out of circuit readings:

1. Black on Source and Red on Drain: 0.539
2. Reverse: 0L
3. Black on Source and Red on Gate: 0L
4. Drain to Gate: 0L

Also, it seems that resistor PR302 gets 19V and outputs 7V. Is this normal? Photo to make things easier



Voltage readings in orange text (as opposed to above, with PQ301 in circuit, and PR301 not in circuit):

put PQ 302 back and remove PR301 from the motherboard and measure the voltage where you now have 1.04v.

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

So these are the current voltage readings with every component in circuit:

[peste]

Re: Troubleshooting: Lenovo Motherboard

read again what I wrote ..

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

PR301 removed and voltage remained the same (first I removed PQ301 by mistake, but then removed PR301). My mistake.

read again what I wrote ..

[peste]

Re: Troubleshooting: Lenovo Motherboard

so, with all the parts on the motherboard, remove only the PR301 and measure the voltage at the point where you have 1.04v in the picture from item # 29.

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Yes, voltage remained the same when removed PR301 (not PQ).

so, with all the parts on the motherboard, remove only the PR301 and measure the voltage at the point where you have 1.04v in the picture from item # 29.

[peste]

Re: Troubleshooting: Lenovo Motherboard

that is all 1.04v?

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Yes do you find it strange?

that is all 1.04v?

[SMDFlea]

Re: Troubleshooting: Lenovo Motherboard

With no power attached test these 3 resistors across pins 1 and 2 of each resistor PR303 200Kohms ,PR307 20Kohms,PR308 68Kohms

[DanFen]

Re: Troubleshooting: Lenovo Motherboard

Assuming the location is fine (I'm in doubt which is which PR308), then the readings seem fine. Uploading some photos: