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

[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

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

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

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

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

Ditto brother...

[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

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.

[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.