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Macbook Pro A1990 - 820-01041 Stuck at 5V / 0.02A [solved]

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datatech85

New member
Hello,
I am working on a Macbook Pro A1990 (motherboard 820-01041) which is not charging.
The Macbook consumes 5V and 0.019A at USB-C.

I've physically separated (by removing F7000 and F7001) PPBUS_G3H and the ISL9240 charging chip to see which side the short is coming from. Removing these fuses gives me 12.6V at the output of the ISL chip (PPVBAT_G3H_CHGR_REG).

However, I can't work out exactly why I don't have the PPBUS_G3H rail.

Here are the values I measured:

PPBUS_G3H: Diode = 0.006 / Resistance to ground = 6.7 ohm
PP20V_USBC_XB_VBUS = 5V
PP3V3_UPC_XB_LDO = 3.3V
PP1V8_UPC_XB/XA/TB/TA_LDOA = 1.8V
PP1V8_UPC_XB/XA/TB/TA_LDOD = 1.8V
PP1V1_UPC_XB_LDO_BMC = 0V
PPDCIN_G3H = 5V
SMBUS_SMC_4_G3H_SDA = 0V
PP3V3_G3H_RTC_X = 0V /Diode = 0.4 / Resistance to ground = 800kOhm

There seems to be a partial short-circuit on the PPBUS_G3H rail as I have 0V on this rail and low resistance.

I noticed that the RB703 and RB731 resistors have lower values than expected: RB703 = 7.3kOhm and RB731 = 16kOhm (instead of 27.4kOhm).

I've tried injecting 1.0V on the PPBUS_G3H rail but nothing heats up and it draws 0.330 Amps maximum.

Don't hesitate to ask me if you need any further information. Thanks in advance!
 
2informaticos

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

Aprox 6 ohm to ground doesn't sink to much current from 1V.
Difficult to detect anything heating with fingers only; IR camera is recommended.

I don't recommend to increase the voltage directly.
Check first if any big coil gets the same reading to ground.
Don't forget L9080/580.
Then we decide if you need to increase injected voltage, or the problem resides into a secondary power rail.
 
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datatech85

New member
Thanks for your quick reply!

I've used a thermal camera to detect a component that's heating up, but I can't find anything that's heating up.

I have big coil near the CPU that gets the same reading to ground (L7420 and L7410)

L9080 seems good as the resistance value starts at 1 mega Ohm and gradually decreases towards 180 kilo Ohm.

Thanks,
 
D

datatech85

New member
I get 0 ohm between these 2 coils : L7410 & L7420 and PPBUS_G3H. Does it mean there is fried component between PPBUS_G3H and CPUGT ?
 
D

datatech85

New member
It's done, I removed U7410 and I have a resistance value between coils L7420/7410 and PPBUS_G3H that increases progressively until infinity! What's more, I no longer have a short-circuit between PPBUS_G3H and the ground :D

Would you advise me to put in a new chip, re-solder the fuses F7000/F7001 and test to see if it works? Or do I need to run more tests to make sure everything's OK?
 
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