820-00165 Works until you plug in battery

[bjf]

This came to us with the smallest amount of corrosion on C5126. I replaced that and U5110. Entire area around SMC, and entire rest of board, was clean. The computer works fine until you plug a battery in. After that the MagSafe light either stays orange or doesn't come on and the computer won't turn on. Any ideas? I'm not sure what would cause this.

 

[CRC2018]

Based upon the assumption you are trying a known good battery:
1) Check PPBUS Voltage is normal
2) check inside the battery connector on the board for any corroded pins - i've seen liquid move down the cable from the battery before and corrode the connector inside.
3) Check R5380, R5381 and R6950

 

[2informaticos]

Post exact voltage and diode mode to ground for SCL/SDA lines of battery bus.
Check if Q7135 is not shorted D-S; between R7120 and L7130.
Also post exact PPBUS_G3H voltage w/ and w/o battery.

 

[bjf]

SCL and SDA are normal at .519 and .518 and 3.4V with normal communication drops when adapter is plugged in without battery.

PPBUS voltage on battery is same as a good board at 7.65V. Voltage while plugged in with battery bounces between 8.1V and 8.3V. MagSafe light goes off. SCL and SDA stay flat at 3.4V.

No short between R7120 and L7130. Diode measurements on Q7130 are all normal.

 

[2informaticos]

Correct PPBUS_G3H is around 8.5V with charger only; check it.
Did you try known good battery?

Post exact resistance between pins 16/18 and 27/28 of U7100.
Also post CHGR_A/BMON levels, w/ and w/o battery.

 

[bjf]

Ok, it just shifted. The SMC is not turning on now, even without the battery. PPBUS is at 8.19V and SMC_RESET_L is down at around 1V and bouncing around a little. This is what it was doing before I replaced U5110.

As I'm writing this I tested 3V42 and the board turned on and works again without battery.

With it working, PPBUS is 8.59V without battery, so that's normal. 3.3 ohms between pins 17 and 18. 20.1 ohms between 27 and 28.

With power adapter-only: CHGR_AMON is at .158V and BMON is at 1.1V and then goes up to 8.59 if I keep the probe on it for a few seconds.
With power adapter and battery plugged in: CHGR_AMON is at .61V and BMON is at .85V. For my tests, I'm using my known-good test battery.

 

[2informaticos]

"BMON is at 1.1V and then goes up to 8.59 if I keep the probe on it for a few seconds."
Are you sure?
CHGR_BMON should be lower than 0.5V without battery.
Now you get stable SMC_RESET_L?

 

[bjf]

Sorry, no, I was still looking at BGATE. BMON is at .63V without battery, and .50V with battery. And yes, I'm getting stable SMC_RESET_L now - with and without battery plugged in - ever since I measured 3V42 and it came back on. Something is unstable on this and appears to be intermittently failing. The liquid-damage was extremely minimal though so it's hard to know what's happening.

 

[2informaticos]

Try reballing SMC...

 

[bjf]

Any idea what would cause SMC_RESET_L to get pulled down like that? I had assumed U5110 but what you're thinking is that it was just the SMC doing it?

 

[2informaticos]

U7100, SMC and U5110 are connected there.
Corrosion at J6100 can also affect SMC_RESET_L.
Also voltages at pins 4, 6, 7 of U5110 are important; so components connected there should be checked too.

 

[bjf]

Thanks, I can't invest the time to reball the SMC but I changed everything around U5110, including a different U5110. We'll see if it holds up. If not I'll sell it as-is to someone who has time to pull the SMC.