Macbook A1502 820-4924-A No power

[piernov]

Re: Macbook A1502 820-4924-A No power

SMC most likely bad, will fail again at one point.

[orion78fr]

Re: Macbook A1502 820-4924-A No power

SMC most likely bad, will fail again at one point.

Yeah sadly.

The battery is not recognized (no info on it in report but removing charger put the device to sleep like it's low percentage) and the trackpad is not detected. Are these signs the SMC doesn't work properly ?

[mon2]

Re: Macbook A1502 820-4924-A No power

Check the voltage to ground of the SMBUS SDA and SCL lines. Measure each and post the readings.

[orion78fr]

Re: Macbook A1502 820-4924-A No power

Check the voltage to ground of the SMBUS SDA and SCL lines. Measure each and post the readings.

SCL (pin 4 of battery) is 2.820 V & SDA (pin 5) 6 mV

[mon2]

Re: Macbook A1502 820-4924-A No power

So SDA is stuck.

Locate and remove D7050 ESD diodes off the logic board.

Test again.

[orion78fr]

Re: Macbook A1502 820-4924-A No power

Removed D7050 & doing the same, 2.8V on SCL & 6mV on SDA, with only battery, only charger or charger+battery

[mon2]

Re: Macbook A1502 820-4924-A No power

Remove all power.

Meter in resistance mode. Measure the resistance to ground of the SDA line.

Compare the resistance against the (working / ok) SCL line.

SMBUS (aka I2C) is an open drain driver. That is, there MUST be local pull-up resistors present on these 2 lines to function correctly.

Respectively, check that the pull-up resistor @ R5380 is present.

Measure the voltage to ground on each side of R5380.

If R5380 is missing or defective, you can have the same fault.

The value for the pull-up is not critical but must be present.

[orion78fr]

Re: Macbook A1502 820-4924-A No power

Remove all power.

Meter in resistance mode. Measure the resistance to ground of the SDA line.

Compare the resistance against the (working / ok) SCL line.

SCL is 2.02 kOhm
SDA is 1.7 Ohm

SMBUS (aka I2C) is an open drain driver. That is, there MUST be local pull-up resistors present on these 2 lines to function correctly.

Respectively, check that the pull-up resistor @ R5380 is present.

Measure the voltage to ground on each side of R5380.

R5380 reads as 100 Ohms
R5381 reads as 2k Ohm

Voltage on R5380 is 3.40 V on the PP3V42_G3H side & 6 mV on the SMBUS_SMC_5_G3_SDA side.

If R5380 is missing or defective, you can have the same fault.

The value for the pull-up is not critical but must be present.

The value of R5380 seems too low, should I swap the resistor ? (the measure is in circuit so it may be 2kOhm but maybe there is a lower resistance path through the SMC)

[mon2]

Re: Macbook A1502 820-4924-A No power

Yes - the resistance does not make sense. If it was this strong, the line should be hard high logic level.

Yes, remove it and then check the resistance without this resistor on the board.

Then replace it with any value of even up to 10k ohms.

[mon2]

Re: Macbook A1502 820-4924-A No power

Forgot to mention it earlier, do remove the battery and trackpad cable. Then measure the voltage to ground again of this smbus line.

Perhaps some short in the trackpad or battery BMS module causing this pull-down fault.

[orion78fr]

Re: Macbook A1502 820-4924-A No power

Forgot to mention it earlier, do remove the battery and trackpad cable. Then measure the voltage to ground again of this smbus line.

Perhaps some short in the trackpad or battery BMS module causing this pull-down fault.

Yeah, last tests were made with the board out of the case (R5380 / R5381 are on back of the board)

Yes - the resistance does not make sense. If it was this strong, the line should be hard high logic level.

Yes, remove it and then check the resistance without this resistor on the board.

Then replace it with any value of even up to 10k ohms.

Still 103 Ohm between the pads of R5380, the removed resistance reads correctly 1.989 kOhm out of the circuit.

Resistance of SMBUS_SMC_5_G3_SDA to ground is 0.4 Omhs, so seems like something is pulling the SDA line to ground.

[mon2]

Re: Macbook A1502 820-4924-A No power

Meter in Diode mode.

Remove all power.

Red meter probe to ground.
Black meter probe to SDA line being reviewed.

What is the reading?

Repeat for the SCL line.

[orion78fr]

Re: Macbook A1502 820-4924-A No power

Meter in Diode mode.

Remove all power.

Red meter probe to ground.
Black meter probe to SDA line being reviewed.

What is the reading?

0.041 V

Repeat for the SCL line.

0.572 V

Almost the same if I reverse the probes (0.041 & 0.653)

[mon2]

Re: Macbook A1502 820-4924-A No power

Yes, this SDA line is shorted.

SMC @ U5000 is the bus master for numerous SMBUS lines including this one.

As per @Piernov's comments (pos #21), SMC may be bad.

1) What are the voltage to ground readings of:

SMBUS_SMC_2_S3_SDA
SMBUS_SMC_2_S3_SCL

Concern is that the trackpad is not working and the trackpad makes use of this SMBUS pair of interconnects.

2) What is the voltage of PPBUS_G3H now with the power adapter?

It should be the wrong value since the SDA line that is used to communicate with U7100 is stuck low. Confirm the voltage.

The SMC often has some underfill / corner glue that with low heat can be wisked away.

If you have no other option - consider to remove this underfill on U5000 with care -> apply flux around each side of U5000 and reflow this IC. That is, apply enough heat and low air pressure (so other parts do not go flying) to make this IC dance with a gentle nudge of the tweezers. The IC will push away a small bit and then bounce back to its natural position. Perhaps this process will correct this fault. If not, then U5000 must be replaced.

[orion78fr]

Re: Macbook A1502 820-4924-A No power

1) What are the voltage to ground readings of:

SMBUS_SMC_2_S3_SDA
SMBUS_SMC_2_S3_SCL

Concern is that the trackpad is not working and the trackpad makes use of this SMBUS pair of interconnects.

3.318 V both

2) What is the voltage of PPBUS_G3H now with the power adapter?

It should be the wrong value since the SDA line that is used to communicate with U7100 is stuck low. Confirm the voltage.

12.27 V

PPVIN_G3H_P3V42G3H is 18.75 V
PP3V42_G3H is 3.406 V

The SMC often has some underfill / corner glue that with low heat can be wisked away.

If you have no other option - consider to remove this underfill on U5000 with care -> apply flux around each side of U5000 and reflow this IC. That is, apply enough heat and low air pressure (so other parts do not go flying) to make this IC dance with a gentle nudge of the tweezers. The IC will push away a small bit and then bounce back to its natural position. Perhaps this process will correct this fault. If not, then U5000 must be replaced.

I will try a reflow then. Warned the owner about the risk, will try this a bit later.
Do you know the size of the solder balls of U5000 ? I ordered solder balls for reballing and a reballing jig but just want to check if I have the correct ball size if the owner wants to swap the SMC.

[mon2]

Re: Macbook A1502 820-4924-A No power

Perhaps wait on others to comment before the SMC reflow but in the past, fluxing and reflowing it worked for other macbooks - likely was corrosion / liquid damage for my case.

Do not know the ball size but often, a smd stencil with solder paste is used + hot air.

[piernov]

Re: Macbook A1502 820-4924-A No power

Pointless to reflow/reball a bad component.

[mon2]

Re: Macbook A1502 820-4924-A No power

Test without the battery to see if the sda line returns to a normal ~3v value.

There is a small possibility that U6100 is pulling down this line. If you feel comfortable, apply flux and remove U7100 and test this SDA line voltage to ground again.

Someone is pulling down this SDA line. It is vital that the pull-up resistor on the SDA line is not defective. If available, replace the pull-up with a fresh one. It can be any value upto 10k ohms or as low as 2k2 ohms.

This case is pointing to a defective SMC as the SMC is the SMBUS bus master.

[piernov]

Re: Macbook A1502 820-4924-A No power

We already know SMC is bad, why keep messing with the rest of the board.

[orion78fr]

Re: Macbook A1502 820-4924-A No power

Pointless to reflow/reball a bad component.

Doesn't cost much to try a reflow aside 10 min & some flux, even though I didn't see sign of corrosion, you cannot always trust what a customer says about a board.
Wasn't going to reball this one anyway, was just asking in case I need to extract another SMC from another board, then I would need to reball it (and it would be my first reballing then).

Test without the battery to see if the sda line returns to a normal ~3v value.

Yeah, already tested without battery. Same.

There is a small possibility that U7100 is pulling down this line. If you feel comfortable, apply flux and remove U7100 and test this SDA line voltage to ground again.

I don't think so, resistance to ground is getting lower the closer you get to the SMC (IIRC battery terminal is 2.7 Ohm, U7100 is 1.4 Ohm and R5380 is 0.4 Ohm, or something like that), so this clearly points towards the SMC.

Someone is pulling down this SDA line. It is vital that the pull-up resistor on the SDA line is not defective. If available, replace the pull-up with a fresh one. It can be any value up to 10k ohms or as low as 2k2 ohms.

Yeah, replaced the resistor after a successful reflow of the SMC (did the tap and solder surface tension pulling it back in place thing), but still the same, booting, no battery recognized, no touchpad.

This case is pointing to a defective SMC as the SMC is the SMBUS bus master.

Going to see with the owner if he want to go that route (changing the SMC).