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820-00165 no power

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andrew boren

Member
i get a amber light for power, board was water damaged, around smc, r5177 -5180 all burned /missing, replaced with good resistors , trace gone at r7516, r8141 was gone. i get 16.4v ppdcin_g3h i get 0v on pp5v_s4rs3. i noticed on alot of the enable lines im getting half a volt.
 
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dukefawks

Administrator
PPBUS, 3V3_S5 present? The usual suspects inspected, U1900, U1950, U6100 and termination resistors and traces, J6100. Probably crap under the SMC too if liquid was nearby.
 
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dukefawks

Administrator
PPBUS? Green orange light even present? Diagnose before just doing a reflow, now there is another variable introduced.
 
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dukefawks

Administrator
S5_PWR_EN present? If no the probably still crap under SMC, pull and reball. If it is present problem will be around TPS51980, commonly corroded trace to pin 23.
 
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andrew boren

Member
im getting 1.7v on pin 2 of r8140 but 3.4v on pin 1, i replaced that resistor from another board, is that voltage right? pin 2 on r8140 goes to s5_pwr_en. r8140 and r8141 were gone when i looked at the board, repaired a trace to r8141 and replaced both resistors.
 
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dukefawks

Administrator
1.7V is way too low. The voltage drop over that resistor is way too high. Either the resistor is dead or there is something pulling it down. Resistance to GND on pin 2?
 
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andrew boren

Member
i may have put the wrong resistor there, the schematics say 100 but not 100 of what, do you know what the resistor is, ill have to pull one from another board
 
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andrew boren

Member
sorry my replys take a bit. ive been doing multiple devices, iphone screen replacements, ipad 5th gen screen, have to balance the board work with priority work
 
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andrew boren

Member
my bad i replaced it with a 100k replaced with right value, now im getting 3.4v on pin 21 of u7501. im getting 1v on c7500 but im getting 8.2v on C7541 and 0v on c7503
 
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dukefawks

Administrator
im getting 1v on c7500 but im getting 8.2v on C7541

Your answer is right there.

But it also seems your PPBUS is at 8.2V which you said was 8.6V earlier.
 
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andrew boren

Member
if they are right next to each other how can it be so low, that would mean something is pulling it down. dont caps short directly to ground so i would get 0v. im assuming c7500 is partly bad?
 
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andrew boren

Member
is there a way to fine the corroded trace? i have been over this board several times and have yet to find anything that looks corroded. anything that had ive already fixed
 
smiba

smiba

New member
You can fix a corroded trace by soldering a wire from point A to point B (In your case from C7541 to C7500), its most likely internal so this is the only option.
 
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andrew boren

Member
sweet, that had worked. i had power, ran it threw ultrasonic, tested, still worked, put it in housing and it stopped working, took it out, tested still dead. i have 8.6v on c7500, 3.3v on c7503, 3.4v on r8140, 1.5v on r7506 instead of 3.3v, 0v on r7551. could the chip be bad? all my problems seam to be around this chip
 
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