820-3115 quarter fan spins in loop

[Bouba148]

BOARD HAD LIQUID DAMAGE AROUND TE EDGE OF THE BOARD (SMC AREA)

PPBUS_G3H : 16,11
PP3V42_G3H :3,476
PPVRTC_G3H :3,317

5V Rails:

PP5V_S5 (PP5V_S5_LDO) : 5,030
PP5V_SUS : 5,030
PP5V_S3 :0V TURNS TO 5V WHEN FAN SPINS
P5V_3V3_SUS_EN : 3,316v
SMC_BATLOW_L : 3,284V
PM_SLP_SUS_L : 3,315v
SMC_RESET_L : 3,444V

3.3V Rails:

PP3V3_S5 :3,297V BUT QUICKLY DROPS TO 1,4V WITH THE QUARTER FAN SPIN
PP3V3_S4 :0v BUT TURNS ON WITH THE QUARTER FAN SPIN

U7200 VOLTAGES:

P5VS3_ENTRIP: 0V
5V3V3_REG_EN: 3,431V
P5V3V3_REG_EN: 3,461V
P3V3S5_ENTRIP: 0,769V


PPVRTC_G3_OUT: 3,316V
SYSCLK_CLK32K_RTC : 32,77KHZ
CPU_VCORE_SO_CPU: 0v JUMPS TO 0,300v WHEN FAN QUARTER FAN SPINS resistance to ground 4ohms,I'm wondering if its not a short to ground?
ALL_SYS_PWRGD: PULSING TO 3,3V
voltage on R5014 IS 3.4V BUT PULSE TO 0V WHEN FAN SPINS
PP5V_S0 :0V BUT PULSE TO 4,5V WHEN FAN SPINS

 

[JohnB8812]

16 volts is way WAY too high on PPBUS_G3H! Replace Q7080, Q7030, Q7055 and the ISL all at the same time. Also check resistance between pins 17/18 and 27/28 of the ISL current sensing can definitely cause this problem.

 

[Bouba148]

Thanks John for your reply. Do you think that if i don't replace everything at the same time there is a risk to blow again ? What if i replace the isl first for example . .

 

[JohnB8812]

Yes it will. If you replace the ISL only and one or any of the fets are shorted, the ISL will die again. Best to replace Q7080/30/35 and the ISL all at the same time to avoid issues. That will likely fix the PPBUS issue. The quarter spin my guess would be current sensing so need to measure resistance between pins 17/8 and 27/28 of the ISL6259

 

[dukefawks]

See if it wants to power from a charged battery. The ISL circuit is not needed for that. If it also does quarter fan spin on battery then there are more issues.

 

[SMMRepair]

Also keep in mind that if liquid hit that SPI ROM chip, it could be damaged...and symptoms would be very similar to what you describe. Swap over another chip (just for testing!) once you address the obviously damaged stuff.

 

[Bouba148]

Hi Dukefawks, JohnB8812, team

The motherboard starts with a charged battery, does that also means that Q7055 is OK? I guess so.....
I've also checked the current sensing resistances between 17/18 and 27/28 and there OK: R7051 is 2,4Ohms, R7052 is 0,2 Ohm R7021 is 10,1 Ohms and R7022 is 10,2Ohms
Q7030 is not shorted between 123 / 5 ,123 / 4 and 5 / 4. Q7035 also is not shorted, i've compared with a good known board.
The same for Q7080
All that to say maybe only the ISL is bad no?

 

[dukefawks]

You should measure directly on the pins 17/18 27/28 to rule out corroded traces.

 

[Bouba148]

OK i think there is some thing bad with the ISL because between 17/18 i have around 311ohms vs 3,5ohms for a good board and for 27/28 it should be OK as i have around 20,5ohms like a good known board.
So i've replaced the U7000:
First i only had ppbus at 8,5V and no fan spin then few min later it came back to 15,90V with quarter fan spin in loop.
Now resistance 17/18 is 244 Ohms and 27/28 is 20,4 Ohms.

 

[JohnB8812]

Resistance between 17/18 is wayyyyy too high. A few possibilities there:

1. R7051 is blown check it again to make sure it’s not
2. R7052 is blown check it again to make sure it’s not
3. R7050 is blown (way less common but in this case could be)
4. The traces between the ISL and resistors or resistors and R7050 are blown which seems like the issue if your resistors all measure in spec

 

[Bouba148]

Hi JohnB8812, Dukefawks, team

it was the 4th possibility: both traces from resistors R7051 and 7052 to R7050 were blown. I've put new traces.
Now fan spins fine at power ON and have a nice 12,71v for PPBUS_G3H but the ISL is getting very hot (can't let my finger on it more than 3-5 sec) so i'm disconnecting the charger to prevent something else to blow.
Do you think this new ISL has been damaged because i've put the power on the board before solving the traces/high resistance issue?

 

[JohnB8812]

Possibly bad soldering or a bad ISL. 12.71 volts is a little high so if a new ISL doesn't bring it down, that makes Q7080, Q7030 and Q7055 suspect

 

[Bouba148]

The overheat was coming from the other side of the board, just at the opposite of R7051 and R7052, where the traces blown it was still shorted to ground. So i removed the short and cleaned the area
you can see it in the attached pictures.
Now ppbus_g3h is fluctuating between 12,44V and 12,51V with average of 12,48V. Resistance 17/18: 2,5Ohms 27/28: 21Ohms
Just have a single quarter fan spin , not in loop
PPVCORE_S0_CPU pulsing once then 0V
Idem if I only plug the battery and short the power pads.If you remember the board was starting with the battery;
If I plug the charger then the battery, all the volatges around the ISL drops to 0V I loose the green light but PP3V42_G3H stays ok and ppbus_g3h to 11,09V which is the voltage of the battery.

 

[dukefawks]

That is a massive short inside the board. This is a write off, RIP.

 

[Bouba148]

Hi duke you can close it, i will use it as a donor board