Lenovo IdeaPad Flex 5 14IIL05, ticking sound

[theManieq]

Hello people
Unfortunately I'm looking for help again. This time the patient is: Lenovo IdeaPad Flex 5 14IIL05. Board LC55-15C 19792-1.

I've bought it completely dead. Shorted main power rail. I found faulty U7205 - NX20P5090UK and PU4501 - TPS51393PRJER. Short's gone. Power suply shows oscillating current, around 20-40 mA. Laptop does not react for power switch and there is a ticking soung from the board.

I traced 20V from jack to PU4403 - dual mosfet FDMS3600. Input of this mosfet is the last place where 20V is stable. On the output it's only 3.4-3.5V, oscillating. Pictures

Suspecting PU4401 - BQ25710 being faulty, I replaced it but with no effect. Now, I have no idea where to look

I've checked both mosfets. They are ok.

[mon2]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Attach the power adapter.

Carefully measure the voltage to ground of each pin of the charger IC (BQ / pu4401)

Post each measurement.

[theManieq]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Pin - voltage

1 - 19.63
2 - 19.52
3 - 19.52
4 - 3.28
5 - 0
6 - 1.57
7 - 6.0
8 - 0
9 - 0
10 - 0
11 - 0
12 - 0.2-0.3
13 - 0.2-0.34
14 - 0.08-0.13
15 - 1.57
16 - 0.04-0.14
17 - 1.2
18 - 3.5
19 - 3.3-3.7
20 - 3.3-3.7
21 - 0.7-0.8
22 - 3.3-3.7
23 - 3.4-3.5
24 - 3.4-3.5
25 - 5.94
26 - 0.05-0.14
27 - 0
28 - 0
29 - 0.13-0.22
30 - 5.9-6.3
31 - 3.4-3.6
32 - 3.4-3.6

[mcplslg123]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Resistance to GND on CLR, no power attached? Resistance mode measurement for dc-in mosfets between
01.pin1-4
02.Pin1-8
03.Pin4-8

[theManieq]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Resistance to GND on CLR, no power attached? Resistance mode measurement for dc-in mosfets between
01.pin1-4
02.Pin1-8
03.Pin4-8

Sorry, I don't get it.

[theManieq]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

OK, I think I know now. So I believe there are two CLR resistors: PR4419 and PR4402. Resistance is in Mohms on both.

DC-in mosfets (PU4408, PU4407):
PU4408:
pin1-4: 147 kohm
pin1-8: Mohm
pin4-8: Mohm

PU4407:
pin1-4: 100 kohm
pin1-8: Mohm
pin4-8: Mohm

[mon2]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Many of the voltage readings of pu4401 are not in range.

Can you confirm the voltage to ground of pin 28 = REGN?

It should be ~6v and matching pin 7 voltage. Suspecting this is a measuring error since pin 7 is ~6 volts and is sourced from the REGN pin.

Remove all power. Meter in resistance mode.

What is the resistance to ground of 19V_DCBATOUT ?

[theManieq]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Sorry, my mistake. Pin 28 has 6V. I double checked all pins and results are the same.

[mon2]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Share the resistance to ground of the main power rail. No power in resistance mode checks.

[theManieq]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Mohms

[mon2]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Resistance is fine on the main power rail.

Suspects are the DCin mosfets and the charger IC.

Remove all power. Meter in resistance mode.

Check the resistance of the first DCin mosfet pair. There are 2 mosfets inside this single package.

This is PU4403.

Check the HIGH side mosfet and LOW side mosfet in the same way.

Meter across the mosfet pins as follows:

Pins 2 & 1 (gate)
Pins 2 & 9
Pins 9 & 1 (gate)

Then repeat for the low side mosfet:

Pins 7 & 8 (gate)
Pins 7 & 9
Pins 9 & 8 (gate)

Post each measurement.

The next dual mosfet @ PU4405 should be checked in the same way.

Post each measurement.

[theManieq]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

PU4403
Pins 1-2: Mohms
Pins 2-9: Mohms
Pins 9-1: 114k

Pins 7-8: 100k
Pins 7-9: Mohms
Pins 9-8: Mohms

PU4405:
Pins 1-2: Mohms
Pins 2-9: Mohms
Pins 9-1: 114k

Pins 7-8: 101k
Pins 7-9: Mohms
Pins 9-8: Mohms

[mon2]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

The resistance is low.

Remove the 2nd dual mosfet and then check the resistance of the 1st dual mosfet that is still on the board.

Check the resistance of the removed mosfet while it is on your work table.

Post the readings again.

[theManieq]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

OK, removed PU4405

PU4403
Pins 1-2: Mohms
Pins 2-9: Mohms
Pins 9-1: 114k

Pins 7-8: 97k
Pins 7-9: Mohms
Pins 9-8: Mohms

PU4405:
Pins 1-2: OL
Pins 2-9: 30k and growing
Pins 9-1: OL

Pins 7-8: OL
Pins 7-9: 1k and growing
Pins 9-8: OL

[mon2]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

For PU4405, these are the measurements with the mosfet removed and being tested on your work table?

[theManieq]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Yes

[mon2]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

These are very low readings. Search out and replace this and also the first mosfet. Purchase a few spares - they should be available on Aliexpress.

Share a link for a quick review before proceeding. The same shop should also have spare charger ICs. Each part will not be too expensive.

[theManieq]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

I have replaced them with AON6912A. They are not the same but similar enough I think. Result is the same - no change. And before you ask: I've also replaced PU4401 - twice. Perhaps the problem is somewhere else.

[mon2]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

Yes, the mosfets look suitable for the replacement.

Remove mosfet @ PU4409 (battery mosfet) and test again.

[theManieq]

Re: Lenovo IdeaPad Flex 5 14IIL05, ticking sound

No change. Besides I have discovered that 3D3V_RTC_AUX is 4.8V. Is it good? With borrowed thermal camera I've also discovered EC getting warm at one point. After removing it ticking sound stopped. All oscillating voltages are now stable. I will order new EC and let you know.