HP G6 MB R13 battery mosfet gets hot when recharging

[Caimano]

Laptop : HP G6 with mb Quanta R13 .
Processor : Intel i5

Laptop could not start and led near dc in connector was off.
Found missing +vh28 : replaced PU2 chip which generates it and PQ52 (second dc in mosfet ).
Now led near dc in connector is lit when on ac power and pc starts and stops fine. Led correctly turns orange when inserting battery with adapter showing that battery is charging.
Everything looks ok, but I found that battery mosfet PQ53 gets very hot when ac adapter and battery are used. I tried replacing PQ53 (the original one tested good after removal), 2 different adapters and 2 different batteries , but same problem.
Here are the voltages on PQ53 :
on ac only : S = 19,5V; G = 19,5V; D = 0,6V (Q53 is cold)
on battery only : S = 10,7V; G = 8,6V; D = 10,7V (Q53 is cold)
AC + battery : S = 19,5V; G = 19,5V; D = 11,5V (Q53 is hot)

I don't see why Q53 gets hot during recharging : any idea or suggestion? Thanks in advance

[mon2]

Re: HP G6 MB R13 battery mosfet gets hot when recharging

Remove all power. Meter in resistance mode, lowest scale.

Check each mosfet to see if it is defective.

Measure the resistance across:

Source (1-2-3) and drain (5-6-7-8)
Source (1-2-3) and gate (4)
Gate (4) and drain (5-6-7-8)

Repeat for each mosfet. Post the readings.

Checking for low resistance on the mosfet = defective and will need to be replaced.

[Caimano]

Re: HP G6 MB R13 battery mosfet gets hot when recharging

I checked resistence between the 3 pins of mosfets PQ23, PQ52 and PQ53 and all readings show high resistence. Measuring in diode mode shows the internal diode as expected. I would say the 3 mosfets are ok, but I replaced them anyway and problem remains.
I found that the 20V ZVS diode PD8 protecting +VAD gets hot when battery is charging. I then checked +VAD and found that on AC only is 19,5V (ok), on battery only is 11,3V (ok), but when battery is charging +VAD raises to about 24V (?!?) as if the charging voltage somehow flows to +PWRSRC and +VAD.
This extra voltage causes PD8 to heat up discharging the extra voltage to ground and PQ53 gets hot too. I am pretty confused why this happens after replacing the battery mosfet .

[keeney123]

Re: HP G6 MB R13 battery mosfet gets hot when recharging

This may be a stupid question but, is the battery good?

[mon2]

Re: HP G6 MB R13 battery mosfet gets hot when recharging

Since the battery can power the laptop, for now do not suspect the battery to be defective.

Remove all power. Meter in lowest resistance mode.

Check the resistance as per above of PQ29 and PQ30 mosfets.

[Caimano]

Re: HP G6 MB R13 battery mosfet gets hot when recharging

I finally found the problem .
I checked PQ29 and PQ30 : ok.
I removed battery charger chip PU9 and checked the resistors and capacitors connected to it and found that PR181, one of the two sense resistors on the charge line was 127 Ohm instead of 10 Ohm.
Replaced resistor and PU9, just in case and PC is working fine and PQ53 is cold even whit battery charging.

Probably PU9 was receiving a wrong feedback from the charging line and behaved incorrectly.
Thanks to the forum for the help provided

[mon2]

Re: HP G6 MB R13 battery mosfet gets hot when recharging

Well done!!

[keeney123]

Re: HP G6 MB R13 battery mosfet gets hot when recharging

I finally found the problem .
I checked PQ29 and PQ30 : ok.
I removed battery charger chip PU9 and checked the resistors and capacitors connected to it and found that PR181, one of the two sense resistors on the charge line was 127 Ohm instead of 10 Ohm.
Replaced resistor and PU9, just in case and PC is working fine and PQ53 is cold even whit battery charging.

Probably PU9 was receiving a wrong feedback from the charging line and behaved incorrectly.
Thanks to the forum for the help provided

That will do it. Good job!