MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powered

[duwane]

Hi All.

I have a very strange issue that I have been trying to fix for a few days now.

Model: MacBook Pro A1278
Logic board: 820-3115-B


Laptop history:
No visible liquid damage/corrosion, but found evidence of other rework (flux) so any signs of liquid may have been cleaned. The laptop went in for a battery replacement but wasn't working afterwards and was deemed unfixable (as told to me by previous owner). Not sure if this was by Apple, or another repair company. The flux found was found around ISL6259HRTZ, so can assume it was replaced at some stage. Also there is one missing pin in one of the memory slots. Looks like it snapped at some stage. The remains of this broken off pin removed by me, so not shorting anywhere.

The issue:
- No boot at all while on charger or battery
- No charger light at all
- 10mA constant current draw from power supply
- ADAPTER_SENSE line is 0v, but not shorted to ground
- SMC_BC_ACOK(CHGR_ACOK) is short to ground, but only when the board is powered (by either adapter or battery)
- PPBUS_G3H fluctuates between 0v and 3v when connected to charger, but voltage drops steadily while measuring towards 0v
- PPBUS_G3H shows 12.33v when connected to a charged functional battery (but SMC_BC_ACOK still shows as short to ground, and still no boot or fan spin)
- Most of the S5 rails not present - due to missing PPBUS_G3H I guess
- PP3V42_G3H is present and measures 3.45v

What I have tried:
I have tried a known working DC in board with the exact same results.
I have replaced the following components with no noticeable changes:
- U7000 (ISL6258) - Replaced 3 or 4 times, so no chance all of these were faulty
- Q7510, Q7520
- U6900
- Checked for shorted caps and bad resistors on the SMC_BC_ACOK line asper touch points indicated by Boardview
I Have removed the following components in an attempt to get rid of the SMC_BC_ACOK short with no results. (I can't replace these as I am waiting for replacement parts to arrive)
- Q7030, Q7035
- U4900 (SMC)
- Q6901

Until I can figure out why there is no voltage showing on ADAPTER_SENSE I am pretty sure I will not be able to get PPBUS_G3H back either. Really baffling me at the moment, and hoping there is something obvious that I am missing? Could there be some sort of short inside the board that only shows up when powered?

Any and all help appreciated!

Thanks.

[mon2]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

SMC_BC_ACOK(CHGR_ACOK) is short to ground

What is the voltage of CHGR_ACIN ? (U7000, pin # 3)

Never mind this measurement - U7000 is working since you have PPBUS_G3H.

Confirm that the soldering is ok for U7000, pin # 14 (CHGR_ACOK).

Confirm that R5087 is present and its value. This CHGR_ACOK is an open-drain output and respectively requires a local pull-up resistor = R5087 in this case to be present. Then R5087 must have a pull-up voltage (ie. PP3V3_S5_SMC) to be function to allow for the '1' state.

After the above, the MAXIM single wire communication IC will be powered to light up the external adapter light.

[reformatt]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

CHGR_ACOK is open drain on ISL chip. Should be pulled high to PP3V3_S5_SMC by a pullup. This comes from the ISL......PPBUS_G3H is 12.3V, this indicates to me that the SMC isn't communicating to the ISL. Most common cause of that is SMC is stuck in reset or issue around the power rails to the SMC.

[mon2]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

Ditto brother...

[duwane]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

What is the voltage of CHGR_ACIN ? (U7000, pin # 3)

Never mind this measurement - U7000 is working since you have PPBUS_G3H.

Confirm that the soldering is ok for U7000, pin # 14 (CHGR_ACOK).

Confirm that R5087 is present and its value. This CHGR_ACOK is an open-drain output and respectively requires a local pull-up resistor = R5087 in this case to be present. Then R5087 must have a pull-up voltage (ie. PP3V3_S5_SMC) to be function to allow for the '1' state.

After the above, the MAXIM single wire communication IC will be powered to light up the external adapter light.

Thanks for the help @mon2 and @reformatt

Have rechecked pin 14 of U7000, and can confirm no short when board not powered.

R5087 is a strange one. Unpowered the value of this resistor shows as the correct value (470k Ohm), but when powered shows as short to ground on pin 1 (as this is SMC_BC_ACOK). The voltage when measured across R5087 pins when board is powered is showing as 3.45v and Ohm value shows as OL.

P3V3_S5 is showing as 0v at this stage.
P3V3_S5_AVREF_SMC showing as 3.28v
P3V3_S5_SMC_VDDA showing as 3.45v

@reformatt PPBUS_G3H is only 12v when a battery is connected. When no battery is connected, PPBUS_G3H only reads as milli volts.

[mon2]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

Do note that resistance checks can only be performed with all power OFF / REMOVED from the logic board.

if you see PPBUS_G3H on with battery only then the battery mosfet @ Q7055 is engaging.

Remove the battery. Using only the external power adapter, post the voltages of the attached points of interest.

Also measure the voltages on both sides of fuse @ F6905.

[duwane]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

Thanks again @mon2

Do note that resistance checks can only be performed with all power OFF / REMOVED from the logic board.

Thanks, yes I realised that after posting. Been a long night/day lol

if you see PPBUS_G3H on with battery only then the battery mosfet @ Q7055 is engaging.

Remove the battery. Using only the external power adapter, post the voltages of the attached points of interest.

Noted. All the S5 voltages I posted in my previous post are with only desktop power supply connected (no battery connected). Only voltage that seems to change between having battery connected and not connected so far is PPBUS_G3H it seems.

Also measure the voltages on both sides of fuse @ F6905.

16.46v measured both sides of this fuse to ground.

[mon2]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

Wait.. you are not using an official magsafe power supply ?

You cannot do that - there is a single wire communication IC from Maxim (formerly Dallas Semiconductor) @ U6900 that will ping the external power supply.

Only the magsafe head (which features a proper single wire communication IC inside as well) will respond to the query.

[duwane]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

Wait.. you are not using an official magsafe power supply ?

You cannot do that - there is a single wire communication IC from Maxim (formerly Dallas Semiconductor) @ U6900 that will ping the external power supply.

Only the magsafe head (which features a proper single wire communication IC inside as well) will respond to the query.

I am using a BY-3200 power cable designed for testing Macs that I got from Union Repair.

I have a second A1278 with the same board in it, and thats what I am basing my findings on. It boots using the same power supply and cable, and even with the same DC In board

[mon2]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

OK. PPBUS_G3H is still a suspect when powered by your external power supply only.

1) Confirm that you have PP3V42_G3H_REG with ONLY the external power adapter (your BY cable should be fine).

2) See post #2 of this thread and review the voltage @ CHGR_ACIN.

Based on the non-existent PPBUS_G3H with the adapter only case, U7000 is not operating properly - for some reason.

Also, be sure that U7000 is being powered via

PP5V1_CHGR_VDDP
PP5V1_CHGR_VDD
PPCHGR_DCIN

3) The power on order chart on sheet # 3 of the schematics will be logical to follow.

[duwane]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

OK. PPBUS_G3H is still a suspect when powered by your external power supply only.

1) Confirm that you have PP3V42_G3H_REG with ONLY the external power adapter (your BY cable should be fine).

Agreed. It is doing my head in lol. I have already replaced it 3 times with new chips, so highly unlikely to be a bad chip, but could be possible I guess.

PP3V42_G3H_REG = PP3V42_G3H = 3.45v as measured @ pin 1 of C6999

2) See post #2 of this thread and review the voltage @ CHGR_ACIN.

CHGR_ACIN (@pin 3 of U7000)= 3.86v - About the same on working board.
PPCHGR_DCIN (Pin 2 of U7000) = 2.36v - This measures 15,9v on the working board, so this could be the main issue. Will investigate this further in bit.

Based on the non-existent PPBUS_G3H with the adapter only case, U7000 is not operating properly - for some reason.

Also, be sure that U7000 is being powered via

PP5V1_CHGR_VDDP
PP5V1_CHGR_VDD
PPCHGR_DCIN

PP5V1_CHGR_VDDP & PP5V1_CHGR_VDD both measure 2.86v. The test board measures 5v for these two, so we have an issue here too grrr.
PPCHGR_DCIN: Currenty measures 2.86v. As mentioned above, will investigate further and advise in a bit if I find anything.

3) The power on order chart on sheet # 3 of the schematics will be logical to follow.

Will work through this and see what I can find, but the 2 lines above that don't match the working board seem like likely candidates?

[mon2]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

PPCHGR_DCIN (Pin 2 of U7000) = 2.36v - This measures 15,9v on the working board

This is major. Review this area carefully. Start with removing all power. Meter in resistance mode.

Check the resistance from the measured pin to a point where you know the power rail is ok. Again no power. This could be trace break or similar.

Compare each measurement to the known good board.

Time for beauty sleep here...my basketball team lost (western semi-final). will check the forum in the morning. Your last post has some good areas to investigate.

For now, do not replace u7000. It may be ok.

[reformatt]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

Check D7005.

Don't replace components en masse unless you have a valid reason. This is a good way to introduce additional faults and then it makes it difficult to help.

All troubleshooting should be done with adaptor only; if you are chasing anything to do with Magsafe, you should always use an original adaptor, trust me.

[duwane]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

This is major. Review this area carefully. Start with removing all power. Meter in resistance mode.

Check the resistance from the measured pin to a point where you know the power rail is ok. Again no power. This could be trace break or similar.

Compare each measurement to the known good board.

Time for beauty sleep here...my basketball team lost (western semi-final). will check the forum in the morning. Your last post has some good areas to investigate.

For now, do not replace u7000. It may be ok.

Fair enough. Thanks for the help so far. Hopefully I will have found the issue by the time you wake up lol

[duwane]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

Check D7005.

Don't replace components en masse unless you have a valid reason. This is a good way to introduce additional faults and then it makes it difficult to help.

All troubleshooting should be done with adaptor only; if you are chasing anything to do with Magsafe, you should always use an original adaptor, trust me.

Thanks @reformatt. I understand, however I don't actually have a magsafe charger for this model sadly, so have no choice at this stage. Also I have no way to tell what current the board is drawing if I use the actual charger.

As far as replacing componenets, I only changed what seemed to not be giving correct outputs, but as you say, this could have introduced other issues, so will slow down on the replacements for future fixes.

Edit. Forgot to mention. D7005 is good Measured with diode test mode. When powered it has 16.45v on both inputs, and the same on the output

[reformatt]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

So if the output of D7005 is ok, that means from your earlier statements you have a 14V drop across R7005? Check R7005 resistance and resistance to ground from pin 2 of the ISL.

[duwane]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

So if the output of D7005 is ok, that means from your earlier statements you have a 14V drop across R7005? Check R7005 resistance and resistance to ground from pin 2 of the ISL.

I rechecked D7005, and yes 16.5v on each ping 1 and 2, and 16.3v on pin 3. Pin 2 of U7000 measures 2.4M ohms to ground (without a DCIN board attached), but the resistance drops constantly until it stabilises at around 1.6M ohm after about 30 seconds after unplugging the power. I removed one pin of C7005 to take it out of circuit, and R7005 gives and immediate value of 300ohm without any fluctuation in value.

R7005 measured inline without a DCIN board attached reads 50k ohm to start with also drops for 20 seconds or so until it stabilises at around 1k ohm. According to the schematic I have, it should be 20 ohm, so must be something else inline that is throwing off the reading.

[reformatt]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

Not sure what your logic is re DC IN board since there is a diode in between, but R7005 is clearly faulty.

[duwane]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

Not sure what your logic is re DC IN board since there is a diode in between, but R7005 is clearly faulty.

Yeah I am trying to find a replacement. The working board's R7005 measures 1kohm, so what should I replace it with? 20 ohm as per schematic, or as per other board 1k ohm?

Regarding the logic with removing the DC IN board, only mentioned it as it has caused different readings with some values for me in the past, so now I remove it before taking any measurements.

Regarding SMC_BC_ACOK, it is still short to ground when the board is powered, which is not correct either I am guessing. Measured using diode tester to ground (positive terminal on ground) it measures a 0.5v drop, but the minute I connect power to the board it direct shorts to ground.

[duwane]

Re: MacBook Pro A1278 - No charger light, no PPBUS_G3H, SMC_BC_ACOK short when powere

Sorry, correction: R7005 on the working board measures 130ohm, not 1k. Measured the wrong one.