820-2850 ppbus_g3h

raainxx

Member
I'm having a hard time with this particular board. It's an 820-2850 with no power:

1. PPBUS_G3H bounces from 12.6v down to 3,5v, then back up. SMC_PM_G2_EN is also pulsing, as are my S5 rails, fan move just a few.
2. PP3v42_G3H stable at 3.42v. Green light solid.
3. Resistance at U7000 (17/18, 27/28) is normal (~3ohm and ~20ohm). Pin 3 of U7000=4V.
4. No power from charger or battery, however, PPBUS does NOT pulse when a battery is connected only (i.e., with battery plugged in, ppbus stays steady), however, the board still will not power on with battery.
5. I can't find a short anywhere; I've checked pp3v3_s5, pp5v_s5, pp3v3_s3, pp5v_s3, pp5v_s0, pp3v3_s0, pp1v05_s5, PPBUS, PP3v42, etc. Couldn't find a short anywhere that might be causing the board to cycle.
6. SMC_RESET_L is stable at 3.4v, however, it drops to 3.3v for a split second every time the board cycles/rails fluctuate.
7. R7020/R7050 measure fine.
8. no liquid or trace on the board.
9. what can i do? do you have some idea?
thanks
 

2informaticos

Administrator
Staff member
PPBUS_G3H fluctuates, is not a classic power cycling...

Stil the same if battery and charger both connected?
Remove F7040 and see if get stable voltage at C7040.

Post voltages at U7000, pins 9 & 15.
 

aprendiz

Moderator
Try to power it on with SMC bypass, must be a sensor issue, look closely with microscope.....
Only charger what do you have on CHGR_DCIN and SMC_BC_ACOK?
 

raainxx

Member
Battery & charger both fluctuate between 11,55V -> 12,46V
i Remove F7040 & i measure on C7040, 12,59V and slow fall to 4V in 3 sec and cycling again.
U7000 9=0V 15=0V
CHGR_DCIN = 16,5V stable
SMC_BC_ACOK=3,25->3,3V
what is SMC bypass?
 

raainxx

Member
I find smc bypass, i press power button and plug the magsafe, nothing on the mac (with or without the battery).
 

raainxx

Member
i don't find anything near TPS51125, seems clean no liquid.
S5 rise 5V and fall directly.
PP5V_S3 stay at 0V
5V3V3_REG_EN=3,3V
 
Last edited:

2informaticos

Administrator
Staff member
"If S5 power good is not coming on PPBUS will start to cycle"
You didn't post P5V3V3_PGOOD yet.
PP3V3_S5 should appear first at L7260; this requires P3V3S5_EN.
Do you get any pulse on these places at least?
 

raainxx

Member
ok i try to change TPS51125 but same problem.
3v3_s5 change between 0V to 3,3V but how can i find an overload on this rail? no short 4,2Kohm
thanks
 

dukefawks

Administrator
Check all other rails for shorts again. 5V_S3 is the first suspect.

What is 3V3_S5 doing with a battery and charger connected?
 

dukefawks

Administrator
5. I can't find a short anywhere; I've checked pp3v3_s5, pp5v_s5, pp3v3_s3, pp5v_s3, pp5v_s0, pp3v3_s0, pp1v05_s5, PPBUS, PP3v42, etc. Couldn't find a short anywhere that might be causing the board to cycle.

How did you miss this?
 

raainxx

Member
i make a mistake when i take the point pp3v3_s3.
i'm here to learn how to repair the board, i can make mistake.
thanks
 
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