820-2850 PPBUS_G3H Trolling Me

supamodz

Member
Working on a 820-2850, customer stated i was doing a party and mac dies in the middle of the session. When i opened the back cover and plugged in the charger the fans are pulsing, not spinning only pulsing. so i started to check the power rails, and ppbus_g3h voltage keeps dropping. It will not stay a solid 12v , it drops to like 4v and spikes back to 12v. I checked current sensing resistors all of them, replaced isl chip same problem replaced transistors, i removed the fuse and checked pin 1 for a short no short i checked caps around area no short I'm completely lost. With fuse off i plugged in the charger and checked pin 1 for voltage same 12v droops to 4v and back up again no water damage board looks fine.What the hell could be the problem here. Please i need help.
 

supamodz

Member
Yes duke i tried with a battery and it won't turn on i read the battery voltage as well i get 10 volts at the fuse steady 10v no pulsing just wont turn on.
 

dukefawks

Administrator
I'm suspecting something in the TPS51125 circuit. Check if the enable P3V3S5_EN is pulsing and if 3V3 output is actually coming high. U7940 is generating RSMRST this way.
 

supamodz

Member
Duke your absolutely right, P3V3S5_EN is pulsing. So what could actually be causing enable to pulse in the circuit? In the schematic it says it comes from SMC_PM_G2_EN does this mean bad smc, or something telling the smc signal to pulse.
 

supamodz

Member
Hardly any power to cpu vcore at all, max voltage 0.030 and back down to 0.000 and back up again you can sort of say its pulsing but not with the proper power.
 

supamodz

Member
no its dead hardly putting out any voltage i doubted it would be on because it needs 3v3_s5 to open the gate
 

dukefawks

Administrator
Well, one of the power rails is not coming on, so it is pulsing. Check all coils and see which one does not pulse, that one is probably keeping ALL_SYS low.
 

supamodz

Member
These are the readings im getting im confused as hell
PPBUS_G3Hpulsing
PPBUS_CPU_IMVP_ISNSpulsing
PPDCIN_G3H17-18V
PP3V42_G3H3.41V
PP5V_S5PULSING
PP5V_S3PULSING
PP5V_S0PULSING
PP3V3_S5PULSING
PP3V3_S3PULSING
PP3V3_S0PULSING
PP1V8_S0PULSING
PP1V5_S3PULSING
PP1V5_S3RS0PULSING
PPVTTDDR_S3When I test this probe fans completely stop pulsing
PP0V75_S0_DDRVTTPULSING
PP1V2_S0When I test this probe fans completely stop pulsing
PP1V05_S0When I test this probe fans completely stop pulsing
PP3V3_S0GPU0.004V
PP1V8_GPUIFPXPULSING
PP1V8R1V55_S0GPU_ISNS0.00V
PP1V05_S0GPU0.00V
PPVCORE_GPU0.00V
PPVCORE_S0_CPUPULSING
PPVCORE_S0_GFX0.00V
PPVCORE_S0_CPU_VCAP0PULSING
PPVCORE_S0_CPU_VCAP10.00V
PPVCORE_S0_CPU_VCAP2PULSING
 

dukefawks

Administrator
I just read you tried a charged battery and PPBUS is 10V? A charged battery should be way over 11, confirm again if this machine is also dead with a known charged battery.
 

supamodz

Member
Hey duke i tested it with a different battery, I get 11.07 v at PPBUS_G3H steady. When i try to turn it on the fans pulse, as soon as i release from jumping pin 5 on the keyboard connector it stops.
 

supamodz

Member
i get what your saying, but where should i start duke. Should i pull coils one by one to see if my voltage gets stable or pull controller chips one by one to get a stable voltage. How would you handle a mess like this?
 

dukefawks

Administrator
Put multimeter on coil and see if something is there. Could also see if you can disconnect the PGOOD signal one by one.
 
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