820-3476 Keeps blowing Q7130

grmacs

Member
This was working off battery only but wouldn't charge. Looked like something was on board that shorted Q7180 to ground pin nearby. REplaced Q7180 U7100 C7125 and DCIN Fuse. I've changed Q7130 4 times now after replacing it short will be gone on pin 1 but if I plug charger in long it will burn Q7130 fairly quickly. I've checked the traces from Q7130 and all has good traces. Tried replacing ISL at the same time as Q7130 but no luck. Any chance the coil L7130 could cause this? Seems like I've seen this before.

Diode at PPBUS_G3H is .138

ISL voltages and resistance look ok other than 18,17,27,28 of course are low.
 

2informaticos

Administrator
Staff member
Be sure about both R/C7125 and their traces/solders to U7100 and Q7130.
Also check diode mode to ground directly on the Gate pins of Q7130.
 

grmacs

Member
TRaces all check out and Q7130 pin 1 is 625 and pin 6 is .465 once Q7130 is replaced and before powering board. If I power the board with magsafe only, Pin 1 will be somewhere around .03 range. Could Q7180 cause it to be burning up? I feel like that is the only major change since I started working on the board unless I shorted something unknowingly checking test points or bad solder on U7100. I say that because originally this board booted off battery and currently that would not be the case.
 

grmacs

Member
I tried swapping Q7180 again prior to powering board but no luck. Diode at pin 1 Q7130 is now .15 after plugging in charger. Pin 6 is still .465
 

2informaticos

Administrator
Staff member
Why do you insist so much to check diode mode on the MOSFET Gates, after applying power?
This is totally irrelvant; it may come to normal values after few minutes.
If U7100 detects a problem, will force off corresponding Q7130 section shorting G-S pins; inside the chip, on the output driver.
When in doubt, remove the MOSFET and check it outside of the board.

Board still works on battery alone?
Did you check resistance between pins 17/18 and 27/28 of U7100?
 

grmacs

Member
Ahhhh ok. Got it. Board still starts with battery.

Yes resistance is good.
Pin 17/18 -3.5 ohms
27/28 - 20.0 ohms
 

grmacs

Member
After checking the chips off the board it doesn't appear they did. I thought low value I was getting on pin 1 was indicative. Q7180 and DCIN fuse are only things I know for certain were broken to start with.
 

2informaticos

Administrator
Staff member
OK, then no danger to connect charger and post U7100 basic voltages; pins 1, 2, 3, 9, 12, 13, 14, 15, 17, 19, 20, 27.
 

grmacs

Member
1- 0
2- 16V
3- 4V
9 - 0V
12 - 3.4V
13 - 3.2V
14 - 3.2V
15 - 0
17 - 1.2V
19 - 5.5V
20 - 5.5V
27 - 1.2V

I've changed Q7180 and U7100 multiple times and same results. I've tested traces from Q7180 also
 

2informaticos

Administrator
Staff member
Post R7185/86 resistance value; measured onboard, ohm scale.
Check their traces.
Also check continuity between R7120 and Q7180.
 

grmacs

Member
R7180/1/5/6 all measure correctly and I have checked for continuity from all points of Q7180 to the according traced points on the board.
 

2informaticos

Administrator
Staff member
Can you post what I asked???

"1- 0"
One of mentioned resistors, or Q7180 is bad; as MOSFET is driven on, but you don't get voltage at R7120.
 

grmacs

Member
Thanks for your help. I DID figure this out. I pulled Q7180 again and under the scope when touching up those pads on the board again there was a little thin layer of pink plastic ribbon on one of the pads. I looked at the bottom of Q7180 and there is a thin layer of pink plastic that was partially damaged and shifted. So I believe when I was pulling them and placing, I used too much heat that was causing that pink layer to get partially damaged. After cleaning up the bottom of Q7180 and touching up the pads on it with some solder prior to placing it back, the board now starts every time. From now on when I change a Q7180 I will use less heat and check the bottom prior to placing it on the board! Oy what a headache.
 
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