(347) 552-2258 [email protected]

820-3662 Boots very slowly. PPBUS is 12.26V

bjf

bjf

Member
This board was hit at the battery connector by liquid. It had 1.8V on SMBUS_SMC_5_G3_SCL. That is back to 3.4V but PPBUS is at 12.26V so I'm not sure what's happening with the SMC. I can't be sure, but I believe PPBUS was at 12.6V because the board was working fine but not recognizing the battery at all. Not sure what might have changed.
 
bjf

bjf

Member
Yes, the SMBUS lines are okay, so i'm trying to solve what signal is being sent to the ISL from the SMC reducing the voltage. I usually only see this when the SMC is not working at all. In this case the computer is actually booting, so I'm not sure what the communication is.
 
2informaticos

2informaticos

Administrator
Staff member
PPBUS_G3H correct level is send by SMC to U7100 via I2C bus (SCL/SDA lines).
U7100 requires high level at CHGR_RST_L also.

SCL is near positive line of battery connector.
I suppose an overvoltage there, because of liquid spill.
Usually SMC is affected, as it is the more sensitive.

Check diode mode (red probe to ground) on both lines; less than 1% difference allowed.
If no good, remove D7050 and check again.
Still bad, check without U7100.
Finally, only remains SMC.
 
bjf

bjf

Member
Thanks, yes, they're good. .504 for SDA and .506 for SCL. Those both have measured fine from the beginning but the voltage was 1.8V on SCL until I ran a little flux underneath the SMC and heated up the area around the SCL ball. I removed the edge bonding before doing that and was careful with the heat. That restored the 3.4V on SCL but then PPBUS dropped down to 12.26V and the computer slowed down. CHGR_RST_L is at 3.4V.
 
bjf

bjf

Member
Yes, normally I would call this a dead SMC but I replaced the 3 resistors above the SMC (R5381, R5361 and R5174) and everything is good now. We'll see where it ends up after final testing, but so far so good. I've never recovered correct data line voltage by reflowing the top of the SMC but I'l be trying it more often now.
 
2informaticos

2informaticos

Administrator
Staff member
When you detect corrosion near SMC is better to reball it.
Heating it with good flux is good for diagnose usually.
You can leave it as is, but do not discard warranty time return...
 
bjf

bjf

Member
Thanks, yeah, I wish I had time but I don't reball or replace SMC's anymore. I just have too many boards to work on. If a reflow doesn't fix it I just sell them as-is, even if I know it's just an SMC replacement or reballing.

As far as holding up, all of our repairs are for computers we bought, and we sell them all with 1-year warranties so if it's going to fail I'm sure it will happen well within that first year.
 
You must log in or register to reply here.
Top