A2338 820-02020-A | Battery Not Detected/Random Reboots

[grimacelord]

Hello,

I have a A2338 MacBook Pro here that came to me because the battery wasn't being detected. The owner tried to replace the battery themselves thinking that the battery was the problem but the behavior continues even with their new aftermarket battery. They also accidentally ripped off the black plastic clasp to the battery flex cable connector @ J5151, but I pulled that off of a donor board and replaced that for them already. I did quickly check to see if that was simply the problem, but it's not.

First thing I checked was I2C_SMC_PWR_3V3_SCL and I2C_SMC_PWR_3V3_SCA in diode mode with no power or battery connected. I found that I2C_SMC_PWR_3V3_SCA is showing a short on that line reading at 0.015V. I2C_SMC_PWR_3V3_SCL reads 0.624V in diode mode. I then checked the schematic and tried removing any of the components on that line that are attached to ground to try and find which component is shorted. I removed U5150, CD201, and UD201, but the short remains. So then I checked to see if there is also a short present on PP3V3_AON and PP3V3_S2, but there is not.

I'm still learning this type of repairs, but from my limited knowledge and looking at the schematic, I am failing to see what other components could be responsible for bringing the I2C_SMC_PWR_3V3_SCA line short to ground.

I am really not sure what I need to check next, so I was hoping someone could help me out here. Thank you.

[mon2]

Post pics of the removed UD201 and U5150 areas of the board.

With these parts removed, there should be no short on I2C_SMC_PWR_3V3_SDA / I2C_SMC_PWR_3V3_SCL.

Remove all power. Meter in resistance mode (not diode mode). Measure the resistance to ground on:

I2C_SMC_PWR_3V3_SCL
I2C_SMC_PWR_3V3_SDA

Post the measurements in ohms.

[grimacelord]

Post pics of the removed UD201 and U5150 areas of the board.

With these parts removed, there should be no short on I2C_SMC_PWR_3V3_SDA / I2C_SMC_PWR_3V3_SCL.

Remove all power. Meter in resistance mode (not diode mode). Measure the resistance to ground on:

I2C_SMC_PWR_3V3_SCL
I2C_SMC_PWR_3V3_SDA

Post the measurements in ohms.

I2C_SMC_PWR_3V3_SCL - (In Ohms scale on my multimeter) reads 0L. (if I set to auto-range - 13.53kohms)
I2C_SMC_PWR_3V3_SDA - 11.4 Ohms

Attached are pictures from the two areas as requested. Please disregard my flux stains that surrounds the area. I will clean that up later. I tried to cleanup the area you're interested in a bit with some isopropyl alcohol so what you're seeing surrounding the area is flux.

[grimacelord]

The only other thing I can think of is the battery flex cable connector itself, J5151. I have removed all of the components on the I2C_SMC_PWR_3V3_SDA line that could be responsible for bringing it short to ground and the short is still there. The only component I haven't removed yet is J5151. Could that be the culprit? And if not, what else could it be? Internal short?

[grimacelord]

Wow. That was it. The connector was the problem. As soon as I removed the connector J5151, the short cleared. Thanks for your help mon2. Solved.

[mon2]

Well done. I was on the sidelines on this one but at least we can agree that it is logical for the suspected region of the defect. Good job!!

[grimacelord]

Back again. Not quite fixed. Removing J5151 did indeed clear the short, but it hasn't fixed the problem of the computer not detecting the battery. I soldered a brand new J5151 connector onto the board, reassembled everything, and the computer still does not detect a battery and the fan spins high. I decided to measure the voltage this time and here is what I have:

I2C_SMC_PWR_3V3_SDA - 0.735V
I2C_SMC_PWR_3V3_SDL - 0.735V
PP3V3_AON - 3.3V

I did change UD201 and U5150 from a donor board, but it made no difference at all. I suppose they could have been bad components from the donor board as well, but the behavior didn't change whatsoever.

Can you help me out again, mon2?

[grimacelord]

Also, I tested for continuity from the test points on the logic board for both I2C_SMC_PWR_3V3_SDA and I2C_SMC_PWR_3V3_SDL to the battery side of the flex cable connector to make sure J5151 was soldered on well and the battery flex cable isn't broken and it's not. There is continuity.

[mon2]

I2C_SMC_PWR_3V3_SDA - 0.735V
I2C_SMC_PWR_3V3_SDL - 0.735V

These are too low. You may be missing the required pull-up resistor on these SMBUS lines or the actual voltage rail for the pull-up resistors. These pins are open-drain by design. They either sink the lines to ground or allow them to float. When floating, you must have external pull-up resistors on each line to park them to the logic '1' state.

[grimacelord]

These are too low. You may be missing the required pull-up resistor on these SMBUS lines or the actual voltage rail for the pull-up resistors. These pins are open-drain by design. They either sink the lines to ground or allow them to float. When floating, you must have external pull-up resistors on each line to park them to the logic '1' state.

Would the required pull-up resistors for these lines be RD207 and RD208? If so, both of those resistors read 6.7kohms, but the schematic says that they should be 4.7kohms. I checked my donor board and they read 6.7kohms on that board as well. Also, if those are the correct resistors, then to me, it looks like PP3V3_AON is the voltage rail for those resistors and I do have 3.3V on that rail.

So if all of that looks alright, could it be that UD201 and U5150 I pulled from the donor board may have also been faulty or would truly faulty UD201 and U5150 present itself differently from what I am seeing?

[mon2]

I think you mean:

UD102
UD150

level shifters? Are these BOTH level shifters onboard? To me, this is a strange arrangement to have 2 different levels shifters with different operating voltages paired together.