MacBook A1278 (3115) No PPBUS_G3H Issue

[pcbmaniac]

Subject: Help Needed: MacBook A1278 (3115) No PPBUS_G3H Issue

Hello everyone,

I'm working on a MacBook A1278 with the 3115 logic board and facing an issue with no PPBUS_G3H voltage. Here's what I've checked so far:

1. U7000 Measurements:
   • Pin 3 has 0V, even though R7012 shows 16.5V from PPDCIN_S5_CHGR.
2. Resistors:
   • I measured R7010 and R7011 with one leg disconnected, and both tested OK.

Based on these findings, I believe U7000 needs to be replaced. However, I have a related question:

• If I also decide to replace the SMC, do I need to order it pre-programmed, or can I program it myself? I have an EEPROM programmer available if BIOS programming is necessary.

Thank you in advance for your guidance!

[mon2]

Remove all power. Meter in resistance mode.

What is the resistance to ground of PPBUS_G3H?

[pcbmaniac]

I measure after fuse F7040 with ground and found about 20KΩ resistane. Also when put DC power about 16,5V, the current is only about 16 mA.

[mon2]

Magsafe led is on? Stable 3v42? Official power adapter?

https://www.badcaps.net/forum/troubl...t-when-powered

[pcbmaniac]

Official magsafe, 3,4V stable, no green light no ppbus_g3h. Please tell me do i need to order SMC pre-programed or i can do it my self?

[mon2]

My understanding is that the SMC needs to be sourced from a donor board. The device details on programming of this component are not public.

Do not believe the SMC is the root cause at this time since the PPBUS_G3H is at 0v. Flux and remove fuse @ F7040. With the fuse removed, do you now have a voltage at the output of the ISL6259 (U7000)?

Pin 3 on ISL7000 cannot be at 0v since this is a simple resistor based voltage divider built by R7010 & R7011.

Meter in diode mode. Remove all power. Touch your meter probes together and there should be a tone beep. Touch one meter probe onto R7010, pin #2. Other meter probe to pin #3 on the ISL (U7000). You must hear a tone beep. If not, there is a pcb trace break that needs to be fixed.

Meter in dc volts mode (30v or higher). Attach the power adapter. What is the voltage to ground at R7010, pin #2? This must be a safe and lower voltage created by this voltage divider. This same lower safe voltage must reach pin #3 of U7000.

Cannot proceed till this is corrected.

https://www.youtube.com/watch?v=oNC1hI0hEsU

[pcbmaniac]

I do a reballing to SMC and i will return.

[pcbmaniac]

Subject: Update: SMC Reballing Attempt

Unfortunately, I wasn't able to reball the SMC because I didn't have the correct stencil. I'll order the appropriate stencil along with some 0.3mm solder balls and will update once I try again.

Thank you for your reply and support!

[pcbmaniac]

Update: SMC Reballing Attempt success but..

After succesfuly rebaling SMC and replacing the U7000, i've managed to get both PP_BUS_G3H at 12,27V and PP3V4_G3H at 3,4V. Unfortunately i cant manage to make macbook operate no green light and no fan spining. Please advise, I can provide all the measurements i can.

[mon2]

Are you using an official power adapter?

Review this flow chart:

https://logi.wiki/index.php/G3_to_S3..._and_Broadwell

SMC is not communicating since ppbus_g3h is low.

Test the voltage to ground of the smbus scl and sda lines on the battery connector.

Magsafe green light will enable after smc is communicating and ppbus_g3h is boosted.

[pcbmaniac]

After many measurements according to diagram mon2 sugested are all corect until, i found that voltage 3,3V_SUS_FET is only 0.3V. I do have at pin (4,7) - 3.3V and at pin (3), 3.3V as well. Any suggestions to go on tomorrow?

[mon2]

Remove all power. Meter in resistance mode.

Measure the resistance to ground of 3,3V_SUS_FET.

[pcbmaniac]

I did measure it and found about 500 ohms.

[mon2]

The resistance is not considered to be a short.

The mosfet @ Q7820 is SIA427DJ and is a P-channel type. So the gate voltage must be lower than the voltage that is being passed between the source / drain pins to enable.

What is the voltage to ground of P5V_3V3_SUS_EN? Measure @ Q7822 (gate pin).

[pcbmaniac]

At Q7822 the gate pin P5V_3V3_SUS_EN is 3.3V

[mon2]

Good. Then this mosfet should be enabled and forcing the resistor @ R7840 to be LOW. That is, when this mosfet enables, the one leg of R7840 will be shorted to ground. Since the pull-up resistor (R7842) is of a much higher resistance @ 220k ohms vs. 3k3 (R7840), the high resistance resistor will lose this battle and allow for this logic low to travel onto the gate of Q7840. However, this is not the case.

So, there may be a damaged trace from the mosfet @ Q7822 (drain pin 3) to the resistor leg @ R7840 OR Q7822 OR R7840 is defective.

With no power to the board, meter in resistance or diode mode -> touch one meter probe to drain pin mosfet Q7822; other probe pin to R7840. In diode mode, you should hear a tone beep. In resistance mode, the resistance measurement should be ~0 ohms. Confirm this important detail. If yes, measure the resistance of R7840. This resistance must be ~3k3 ohms. If not close to this value, the resistor could be defective.

Finally, if the above values are ok, flux and replace Q7822 which is most likely defective it you do not observe a low or 0 volts on the gate of Q7840.

[pcbmaniac]

Since i use schematic PDF 820-3115, the part numbers and some values are different but the principal is the same. For now i must go to sleep. We can continue tomorrow at noon. Thank you for your help.

[mon2]

Yes, do review but my schematic is supposed to be also 820-3115. Post this section of the schematic tomorrow to continue. There is a fault in this region based on the shared measurements.

Update - I see my error - there are 2 mosfets inside of Q7822. Each gate of these mosfets is linked to the same drive signal. Trace your board for the NORTH half of the schematic shared below. There is a fault in this region.

Q7820 is not enabled because the mosfet (1/2) that is linked to R7820 is not low. This implies that Q7822 is defective OR there is a trace break to R7820. Once Q7822 enables, the gate of Q7820 must be low. Since the gate of Q7820 is at 3v3, the resistor @R7820 is ok.

Also review the resistance across Q7820 to rule this part as being defective.

Measure the resistance of:

source / drain
source / gate
gate / drain

Each should be hundreds of k ohms or higher. If not, then this mosfet could be leaky.

[pcbmaniac]

I did measures and find that PM_SUS_EN is missing. Since i dont have a replacement chip U7940, i put the missing resistor 0 ohms R7917 and now i do have both PP5V_SUS = 5V and PP3V3_SUS =3.3V. Then i noticed that signal S5_PWRGD is 0V. What to do next?

[pcbmaniac]

Any chance to fix my old macbook by reheat in the point of pins under chip SMC? Any other ideas?