Lenovo Legion 5 Pro 16ACH6H Water Damage

[Andreasbest]

Test the resistance across the 2nd dcin mosfet.

source / drain
source / gate
gate / drain

often 2nd dcin mosfet is defective and takes down the 1st dcin mosfet since they share the gate pins.

no power to the board during these tests.

S - D 7ΜΩ
S - G 7.19ΜΩ
G - D 12ΜΩ
With mosfet soldered on board.

[khaahk]

I was wrong about the work from battery, from the datasheet we read :

7.3.1.1
Battery Only
When VCC voltage is above UVLO, bq24780S powers up to turn on BATFET.

This is the PQ5403 on schematic, it connects the battery voltage to B+.
So this mainboard does not work without the charger ic.

I don't know no checks that can be done, it is ic-s internal fault. If mainboard has no further problems then it probably should work from battery.

[Andreasbest]

So i must order a new PU5401 to replace it and test it again, correct?

[khaahk]

So i must order a new PU5401 to replace it and test it again, correct?

Yes

[Andreasbest]

Ok, ordered 5 pieces. When they come i'mm come back with results

[funnypenguin]

Sorry to jump in on this one. I'm working on the same laptop that seems to be going through the same thing, no signs of life. Here's what I have so far. If anyone has any ideas or input I would be super greatful! I'm thinking maybe get a new 24780s?

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Resistances

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DC in MOSFETS

PQ5401, gate source drain no shorts

PQ5402 gate source drain no shorts

Main Power Rail to Ground 3 Mega Ohms


Current sensing lines

AC input current sensing amp inputs .7 ohm

Batt Current sensing amp 20 ohms

ACOK (pin 5) to ground .47 MegaOhms


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Voltages

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Main Power Rail Check

@ PR5401 Fluctuating 3.1-3.3v, not fully shorted.

Charger IC voltages


REGN (pin 24) 6.04v

VCC (pin 28) 19.7v

ACDET (pin 6) 2.62v

- TI manual says greater than 2.4v should be ok?

CMSRC (pin 3) .03-.35v

- Should be close to AC? something wrong?



ACDRV (pin 4) .02-.35v fluctuating with CMSRC and Main Power Rail.


ACOK (pin 5) 0v

[Andreasbest]

Replacements of charger ic arrived, you want to replace it and try if it power on OR you want to take any measurements before I connect power?

[khaahk]

Make the replacement, if there are any problems then take measurements, with liquid damage everything is possible.

[Andreasbest]

Sorry for the delay, got a problem.
Here are the measurements:

PR5401 16Ω on both pins to GND

PU5401 voltages:
pin5 0v
pin6 2.68v
pin24 6v
pin28 30v

Just replaced it.
Still no power, voltages the same, except the pin 6 now gives 0.5v
Replaced it with 24780 not 24780S, this is what the supplier sent me and as i read here it's compatible.

[khaahk]

I don't know why but somehow i missed the PR501 ohms reading on your original message. This means that you have low ohms on main power rail B+, meaning you might have some high side mosfet failure or some component failure on main power rail. Why is pin6 low - maybe bad connection or bad chip. Try to measure resistance to gnd on all coils - try to find the 16 ohms reading which might indicate the failed part. For now you can ignore the PU5401 - first you need to deal with the main power rail.

[Andreasbest]

PL1009 has the same resistance to GND as PR5401.
Plus i get beep when i connect probes to PL1009 and PR5401, seems they are in same rail.

[khaahk]

Then PQ1005 is a suspect, remove it and see if resistance on PR5401 goes higher. If so then the PQ1005 needs to be replaced, hopefully the cpu survived the failure, resistance reading gives some hope but ...

[Andreasbest]

Then PQ1005 is a suspect, remove it and see if resistance on PR5401 goes higher. If so then the PQ1005 needs to be replaced, hopefully the cpu survived the failure, resistance reading gives some hope but ...

Removed PQ1005 and now the resistance on PR5401 is several KΩ. So i replace it and resolder back the old 24780s?

[khaahk]

Probably the old 24780s is good, do you have a replacement for PQ1005? - it is a dual mosfet.
At the same time you can make resistance measurements on PU1006 pin 3,7 and 8 to gnd, looking for abnormal low resistance, it might be damaged due to PQ1005 being shorted.

Removed PQ1005 and now the resistance on PR5401 is several KΩ. So i replace it and resolder back the old 24780s?

[Andreasbest]

3 16K
7 7.2K
8 10k
I'll solder back the old charger ic as i trust it more than the chinese replacement, not sure about MOSFET, i'm checking on donor boards now.

Found several Z998 they look compatible, can you confirm please?

[khaahk]

Layout is a little different, also less powerful. Try to find some other options.

[Andreasbest]

Checked 12 motherboard. not able to found this or anything compatible, very powerful and dual mosfet, rare.
Ordered some, i'll get back when they arrive. I think this was the cause of the problem and i hope CPU is not damaged.