820-00426 - charging circuit - U7100 gets warm

[Rper123]

Hi,
Came in with U7100 blown. Replaced it, Q7130, Q7135, Q7155 and R7105 (measured kohm instead of 20ohm) also. U7100 got warm so I replaced Inrush Limiter mosfets from a donor board (in this model there are 2 mosfets but in schematics it shows only one - Q7180). U7100 still gets warm. Measured resistance on every pin on U7100 and nothing is wrong.
I tried charging the battery and CHGR_PHASE measures about 13,2V which normally is 12,6V.

 

[2informaticos]

Did you check exact voltage at F7140/41?

Post exact resistance between pins 17/18 and 27/28.
Also post basic voltages; pins 1, 2, 3, 9, 12, 13, 15, 17, 19, 20, 27.

 

[Rper123]

Strange. Now voltage at F7140/41 is 4V. U7100 still gets hot.
Resistance between pins 17 and 18 is 3,8 ohm. Resistance between pins 27 and 28 is 22,8 ohm.
Pin:
1=0V
2=18,9V
3=3,4V
9=0V
12=3,4V
13=3,34V
15=0,067V
17=4,1V
19=4,99V
20=4,6V
27=20V

 

[2informaticos]

"19=4,99V
20=4,6V"
Seems to have bigger difference than expected there.
Try abother ISL6259.
Be sure C7125 is OK.

 

[Rper123]

You had right. Pin 23 and 25 (CHGR_BOOT and CHGR_PHASE) are shorted (0ohm between) and R7121 and R7122 measures in kohm in stead of 20 ohm before. just replaced U7100 and after plugging power in measured 1,6V on CHGR_PHASE. Disconnected power and CHGR_BOOT and CHGR_PHASE again shorted.

 

[2informaticos]

"replaced U7100 and after plugging power"
NEVER do this again.
After replacing burnt component, check first in diode mode around it.

This "short" may not exist; is how the chip blocks high-side MOSFET, when detects a problem.
Did you check C7125?
R7121/22 can both burn only if bad ISL6259; less chance that C7121/22 get shorted at same time...

 

[Rper123]

I have checked in diode mode first
It seems that replacing U7190 (P5V1) was the problem all the time. Now stable 5,1V at P5V1_CHGR_VDD and P5V1_CHGR_VDDP.
U7100 doesn't get hot and the battery is charging.
Thanks a lot for your help