[SOLVED]820-2879 Q7035 Keeps shorting to gnd

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TCRScircuit

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820-2879 came in not powering on w/ No water damage. Found dead short on PPBUS_G3H... Ran power found Q7035 getting very hot... Replaced it short gone, Got a green light w/o fan spin... PPBUS_G3H voltage was 3v. ISL had a hole burned through it so I replaced it.... No green light... Checked my soldering and even tried a new chip. I decided to measure PPBUS_G3H again and it was dead shorted AGAIN. Ran power, found the same mosfet getting hot... Removed it and short gone.... Stumped... What could keep causing the mosfet to burn out. Thank's Duke or Louis in advance.
 

aprendiz

Moderator
Replace U7000, Q7030 and Q7035 at the same time, aslo check R7005 and resistance between pin 17/18 and 27/28........

Resistance between pins 27/28 should be about 3ohm
Resistance between pins 17/18 should be about 20ohm
 

TCRScircuit

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Had 2 mosfets come in for another 2879, So I replaced both Q7035 and Q7030 and shorted again... Clueless
 

TCRScircuit

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Got the mosfets.... Replaced them and the ISL... No change... r7005 is good.. PPBUS_G3H still dead w/o green light.. No short to ground on PPBUSg3h or pp3v42. Replaced u6900 and u6901 as well with no change.... PP3V42 is present and chrgr L gate has continuity to mosfets from ISL..
 

TCRScircuit

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It's the SMC. Sysonewire is missing... Replaced u6900 and u6901.. SMC BC ACOK is present but still nothing. This is a rabbit hole.
 

TCRScircuit

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dukefawks This is is really strange.... Replaced the fets... Replaced the ISL... R7005 is good.. Current sense is good... PPBUS is dead.. 3v42 is good... Don't know what else it could be... No shrt on PPBUS either... Maybe something to do with SMC_BC ACOK?
 

TCRScircuit

Super Moderator
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I think I am getting trolled by a bad from the Reel ISL.... ACOK was low I believe.. I'll take another shot at in a day or so... No voltage on Chargr L Phase... It had PPBUS G3H before I replaced the fets and the ISL but it was high at 16V... So i think I just put on a dud ISL... Will update. And yes current sense is OK. No Green light..
 

TCRScircuit

Super Moderator
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dukefawks OK... I have restored PPBUS. However, Still no green light.. I'm thinking bad SMC or u6900...

Adapter Sense = 1.09v
Sys One wire is jumping between .30 and .75 v
SMC BC ACOK _VCC is 0.13 v
SMC BC ACOK is 3.21 v
PPBUS_G3H is 12.23v So the SMC is on?
PP3v42 is 3.42v ....

So right now I am leaning towards a dead SMC or dead u6900...
 

jgraffis

New member
looks more like something is bringing SMC_BC_ACOK_VCC down. i would remove u6900 and test for voltage at pin 1, if voltage is back to 3.4v (assuming you've already replaced the magsafe jack) then i would say smc issue try reflow if same issue replace smc.
 

jgraffis

New member
didnt want u too reball the smc. what was the voltage on pin 1 of u6900 after you removed u6900? this would have told you if u have an issue on the sys_onewire bi-directional line. this still doesnt eliminate a bad smc. Lets hope u didnt reball a bad smc.
Remove u6900, plug in and see what the voltage is at pad #1 of where u6900 used to be. what is the voltage?
 

TCRScircuit

Super Moderator
Staff member
jgraffis I know you didn't want me to reball it, But I wanted to do it just to rule out if there was crap under it... The voltage was the same on SMC_BC_ACOK_VCC with u6900 removed ,I forgot to include that in the above post.
 
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