[SOLVED]820-3024 (another) - SMBUS_SMC_BSA_SDA line droop

[2andrewd]

I purchased this board, came fully functional aside from not recognizing battery. Looks clean, no evidence of liquid.

U7000
Pin 11 3.4v stable
Pin 10 SMBUS_SMC_BSA_SDA moves between 3.4v - 0.15v


R5280 2K
R5281 2k
SMBUS_SMC_BSA_SDA is stable at 3.4v on pin 1 of R5280 while pin 2 measurement behaves as stated above.

Data line troll fix suggestions?

 

[larossmann]

That is the point. The SMC, ISL6259, and battery communicate on that line by dropping it from 3.42v to 0v by shorting to ground to create pulses. Those pulses are the communication. The SCL and SDA line should have something like 0.441 diode mode measurement to ground on them with red probe on ground.

Check PPBUS_G3H, if it is 8.16v and the pullups & traces are fine, most likely bad SMC.

 

[2andrewd]

Shiiioot. 8.26 on PPBUS_G3H.
V to ground on both lines are good. Anything else to check before the bullet bite? And... What are the odds that a reflow will bless this thing? There are a few red TP's around the SMC, I suppose it's worth trying. You may be selling an smc stencil soon.

 

[larossmann]

You can always try reflowing it but I doubt it

 

[2andrewd]

Got it. Why do failed smc's pull down ppbus_g3h and is that always an indication of it's state?

 

[2andrewd]

I forgot I borrowed some fb resistors from from u7400, replaced &. ppbus_g3h back at 8.4. but no orange julius!
Relowed smc..battery <---> smc now chatty cathy.

this one is a wrap. thanks louis!

 

[G.Beard]

I forgot I borrowed some fb resistors from from u7400, replaced &. ppbus_g3h back at 8.4. but no orange julius!
Relowed smc..battery <---> smc now chatty cathy.

this one is a wrap. thanks louis!

When I have reflowed SMC, the board comes back to haunt. I would replace SMC.

 

[2andrewd]

Noted. I've never attempted any BGA rework before but looking like it's gonna be a cornerstone.