820-00165 no green light (possible short on pp3v42_g3h)

Gmorb

New member
customer stated they left it charging overnight with an external HDD plugged in and it just stopped working.

did extensive troubleshooting and found out theres what seems to be a short on pp3v42_g3h (multimeter beeps when checking)
now in these cases id do the usual inject voltage to find what component is shorting but my power supply doesnt detect a short.
it pushes 3.42v at 0.700A I removed a lot of caps to try and find the short even smc but i still get beeps.

any tips of how i can find this short or is it most likely within the board?

i compared to another mac of the same model and the known good doesnt beep at all on 3v42_g3h i also get 8kohm resistance to ground on the good one and 1ohm and dropping on the bad one.
 

2informaticos

Administrator
Staff member
1ohm is really short.
But do not believe beep is always short.
Some multimeters beep untill 075...

But 1ohm there should generate more than 3A when inject.
Check value in ohm scale (200ohms), not buzzer mode.

Short on 3V42 is not usually generated by a cap; all are 6.3V at least.
U7000 is a good suspect here, as U4650 too.
I suppose you disconnected SSD, trackpad and LIO flex.
 

Gmorb

New member
I removed both of those in the process of troubleshooting even the resistors that communicate with u4650 and still got beeps. Maybe i should start removing caps around u7000?
 

2informaticos

Administrator
Staff member
"Short on 3V42 is not usually generated by a cap; all are 6.3V at least."
I still doubt about any caps. Could be, but left them at the end...

On the 3V42 line are more chips connected; remove all of them.
 

Gmorb

New member
hey thanks for the advice so far I narrowed it down to smc being the cause of the short. now the short is gone and I installed a good smc but upon powering on r7005 blew. replaced it with a good one now i only get about 14.75v shooting out on pin 2. when i remove d7005 it fluctuates from 16v to 15v. something bringing it down?

update: damn short came back on 3v42. tested with power supply again and this tme i can feel the smc getting really hot.. smc keeps shorting..
 
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2informaticos

Administrator
Staff member
Possibly overvoltage on 3V42 line.
You must get 3V42 at C7098/99 whitout SMC.
Don't solder new SMC until get correct value.
Pay atention to R7095/96.
Open R7095 (corrosion) will increase 3V42 over 7V...
 

Gmorb

New member
ok yes there was over voltage and after replacing r7095/96 it went back down. now question is are my smcs fucked? i only had 1 :/ is it possible it may still work.
 

2informaticos

Administrator
Staff member
you can locate 3v42 and ground pins on SMC, comparing with boardview.
So you can measure on the SMC pads, not soldered.
If no short on 3V42, you can try it at least...
 

Gmorb

New member
So the one i thought was bad was actually good since it didnt get 7 volts to it. Now it boots thanks for the help!

no theres just one more issue. the fans kick in high only clue i see is palm rest temps are 128 degrees and i dont know where the thermal sensor for that is any ideas? may it just be the smc since it may have taken some damage?
 
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2informaticos

Administrator
Staff member
Palm rest, its name make me think about trackpad, isn't?
Try new cable first.
Next, clean the trackpad circuitry and connectors.
Finally, change the trackpad...
 

Gmorb

New member
I tried a known good same issue. Also mainboard proximity is high 128 any idea if that sensor exists somewhere?

im starting to think this maybe an smc issue could it have gotten slightly put out of wack due to the prior fault?
 
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