Lenovo IdeaPad 330 laptop mosfet issue

[ebyte64]

Good day everyone.

I have been scratching my head with a Lenovo laptop I got in today.

The laptop had no power and taking no amps from the power supply. Checking voltage showed 20v only on one side of the first mosfet. Took it off and replaced it and then same story. Took off second mosfet and then the first mosfet had the right voltages as well as 25v on gate is it should. Replacing the second mosfet the problem started again.

Even using a wire to bypass the second mosfet does the same interference with the first mosfet.

Would anyone have any idea why?

[mon2]

Re: Lenovo IdeaPad 330 laptop mosfet issue

Are the mosfets known good and of the same type? That is, N-channel mosfets?

Remove all power. Meter in resistance mode.

Check the resistance to ground of the main power rail that follows the 2nd DCin mosfet.

What is the measurement?

PS: never bridge the mosfets. If it could be done, the vendor would have done so to save a few pennies.

[mcplslg123]

Re: Lenovo IdeaPad 330 laptop mosfet issue

Very likely one of the mosfets is shorted or leaky near charging coil. Check them one by one. 2 mosfets for charging coil(Upper and Low side) and another for discharge has to be checked in resistance mode.

[ebyte64]

Re: Lenovo IdeaPad 330 laptop mosfet issue

The resistance measurement after the second mosfet is 5.6 mega ohm. I have just to test bypassed both mosfet and the board does come on then and I can boot into windows. But that was just to test I will of course not leave it as is. Also the mosfet I have used are known good. I did check them beforehand.

[mon2]

Re: Lenovo IdeaPad 330 laptop mosfet issue

Link the schematic if available in the schematic forum.

What is the charger IC on this board? This charger IC will drive the gate pins of the 2*DCin mosfets.

Does the first mosfet behave normally if the 2nd mosfet is removed? Post the voltage to ground of each pin on the 2*DCin mosfets.

Source
Gate
Drain

Then remove all power. Meter in resistance mode.

Measure the resistance of:

Source and drain
Source and gate
Gate and drain

Pins of each mosfet, while each is on the board. If the mosfets are known good then the fault is elsewhere but need to study the schematic.

[ebyte64]

Re: Lenovo IdeaPad 330 laptop mosfet issue

Thank you for your time the first mosfet behaves normally without the second mosfet on the board.

First mosfter voltages:

Drain: 19.6v
Source 19.6v
Gate 25.6v

As soon as you add the second mosfet the voltage on source and gate becomes very eratic. 15 to 18v

The resistances of the first mosfet :

Drain to source 3.8m ohm
Drain to gate 6m ohm
Source to gate 3.9m ohm

The charging ic used on this board is the bq24708s

I wish I had a schematic for this board but unfortunately I do not.

[mon2]

Re: Lenovo IdeaPad 330 laptop mosfet issue

The charging ic used on this board is the bq24708s

bq24780s ?

This chip is well documented. Suggest to download the datasheet for this component for a deeper study.

https://cdn.badcaps-static.com/pdfs/...2a8abce3d9.pdf

Focus on the region with the current loop resistor. Suspecting that there is no fault in the 2*DCin mosfets nor the boost voltage required to enable each of the 2*DCin mosfets. That is, you have ~25v on the gate pin till both of the mosfets are soldered in place.

Also, you know from the bypass method with an external DC power supply, the logic board works normally. The difference is that the charger IC is no longer involved in the decision making process.

Respectively, the charger IC is involved once you restore the mosfets to be both onboard. It is very possible that the fault is in the current sense resistor circuit that follows these 2*DCin mosfets.

Remove all power.

Meter in resistance mode.

Measure the resistance between the pins of the charger IC, pins #1 & #2 (ACP & ACN).

Post the measurement. Be sure to measure directly at the charger IC and again, with NO power to the logic board / no battery attached.

PS: Is this the IDEAPAD 330S ? If yes, found the schematic in my paid service.

[ebyte64]

Re: Lenovo IdeaPad 330 laptop mosfet issue

I get 1. 3 ohm between pin 1 and 2

[ebyte64]

Re: Lenovo IdeaPad 330 laptop mosfet issue

Ah thank you so much for the schematic. I only have the board with me right now but I will 100% sure if it is the right model.

[mon2]

Re: Lenovo IdeaPad 330 laptop mosfet issue

What is the resistance if you short your meter probes?

[ebyte64]

Re: Lenovo IdeaPad 330 laptop mosfet issue

0.3 ohm

[mon2]

Re: Lenovo IdeaPad 330 laptop mosfet issue

Ok. To me, the path between ACN & ACP is too high.

Measure the resistance from ACP to the mosfet Q5902 - should be 0R3.

Then measure the resistance from ACN to the main power rail (C879) - should be 0R3.

This is to confirm that the traces BEFORE and AFTER the current sense resistor are ok.

The current sense resistor between ACN & ACP should be 10mohms = 10 milli-ohms. Respectively, with your meter, it should appear like 0R3. Only a very high quality milli-ohm meter can measure the true 10mohm value.

Perhaps wait on others to comment but consider, if available, to replace the current sense resistor @ R5903.

[Vesko356]

Re: Lenovo IdeaPad 330 laptop mosfet issue

I wish I had a schematic for this board but unfortunately I do not.

PS: Is this the IDEAPAD 330S ? If yes, found the schematic in my paid service.

Schematic ---> https://www.badcaps.net/forum/showth...26#post1215826

.

[ebyte64]

Re: Lenovo IdeaPad 330 laptop mosfet issue

mon2, thank you so much for your help. It was the current sense resistor.

[mon2]

Re: Lenovo IdeaPad 330 laptop mosfet issue

Awesome! Now, I just need some of that good luck to fix the units others have rejected around town. So much garbage out there..

[ebyte64]

Re: Lenovo IdeaPad 330 laptop mosfet issue

I am sure you will be able to fix them.