820-3437 Board with PPBUS_G3H at 8.18v

[tlough75]

So I am working on a MBA with an 820-3437 board. PP3V42_G3H is steady at 3.42v, but PPBUS_G3H is 8.18v. I checked the resistance of pins 27 & 28 of U7100 and get 20.2 Ohms and 3.3 Ohms on pins 17 & 18. I checked in diode mode on L7520 and it comes up as .01v drop on both sides. Not sure where to go from there.

 

[2informaticos]

Start checking SMC_RESET_L, if no Magsafe light present.
Next, diode mode to ground on SCL/SDA lines of battery bus; also check the voltage.

 

[tlough75]

Start checking SMC_RESET_L, if no Magsafe light present.
Next, diode mode to ground on SCL/SDA lines of battery bus; also check the voltage.

No Magsafe light is present.

SMC_RESET_L is 3.37v

SCL:
Diode mode is .540v
V= 2.72v

SDA:
Diode mode is .537v
V=3.42v

 

[2informaticos]

"V= 2.72v"
Are you sure about this?

Change ISL6259 first.
If still the same, change SMC.
You can try to reflow/reball SMC before replace it.

 

[tlough75]

"V= 2.72v"
Are you sure about this?

Change ISL6259 first.
If still the same, change SMC.
You can try to reflow/reball SMC before replace it.

Double checked SCL and it is 2.72v. I will replace the ISL6259. If that doesn't work I will first reflow then replace SMC & report back.

 

[tlough75]

Changed ISL6259 and still the same. I tried to reflow SMC but it came off board... Looked like some pads on the bottom of the chip were gone. So I will replace it.

 

[2informaticos]

Please do NOT quote an entire post, visible few centimeters above.
Try to maintain forum aesthetics...

 

[tlough75]

Got it. One question: Before replacing the SMC I found PP5V_S4RS3 is shorted. I tested via L7520. Even with the SMC removed. Is this a separate issue? Can I remove L7520 and inject voltage here to find a short? I checked this vs 5 other working machines and found that the short I am getting is an abnormal condition. This is not a customer machine BTW, just an experimental project of mine. This is by far the most interesting issue I have ran into so I am pursuing it for the understanding and education.

 

[2informaticos]

Why did you remove SMC?
It is not connected to any 5V rail.

You can try injecting voltage; if is really short, or very low value to ground.
Start with 1V and go up...

 

[tlough75]

I removed the SMC by accident... I had the air up on my hot air station up too high and not enough flux. Doesn't help that I am now using a bent nozzle when I am used to straight ones. Before I took it off I noticed the that the goo on the corners of the SMC was brown like someone burned it. I'll try injecting voltage starting at 1v. This should be fun...my thinking is that this board has more than one issue. I can definitely tell it has been messed with before. The hold down tab on the keyboard connector is gone & the battery connector is a little melted. Like someone baked the board. This came out of a MBA that someone gave to me as they bought a new machine so if I mess up I am not out any money but if I manage to get somewhere I got priceless knowledge!