820-3115 Power Issues

[hambook]

Hi all, I have an 820-3115 that is having issues. Came in with no liquid damage, customer reported they were watching a movie and it shut off unexpectedly. I get intermittent green light but it only pulls 0.013A from the bench PSU. Found that PP5V_S3 was shorted to ground (0.30ohm) and injected 1v, found C6213 to heat up so I removed it. Short is clear now but still not getting PP5V_S3.

PPBUS_G3H: 12.6v
PP3V3_SUS: 0v
SMC_ADAPTER_EN: 0v
PM_DSW_PWRGD: 0v
PCH_DSWVRMEN: 3.3v
PM_BATLOW_L: 0v
PCH_SRTCRST_L: 3.4v
PPVRTC_G3H: 3.4v
RTC_RESET_L: 3.4v

 

[2informaticos]

Post U7200 basic voltage; pins 16, 13, 3, 8, 17, 6.
Do you get SMC_PM_G2_EN?

 

[hambook]

U7200
3: 0v
6: 0v
8: 0v
13: 3.4v
16: 12.6v
17: 0v

SMC_PM_G2_EN: 3.4v

 

[2informaticos]

Check diode mode to ground at VREF and VREG3/5.

 

[hambook]

VREF: 687
VREG3: 464
VREG5: 516

 

[2informaticos]

Then change U7200.
Be sure to have good solders and traces.
Also check diode mode to ground at L7220/60.

 

[hambook]

Changed U7200, double checked all the solders/traces. Am now getting
VREF: 679
VREG3: 637
VREG5: 503

L7260 seems really low, diode is 144, L7220 is 390. Does this mean something is pulling PP5V_S3 down?

 

[2informaticos]

Post again U7200 voltages; above mentioned pins.

 

[hambook]

Whoops, sorry. Completely forgot to check again.

U7200
3: 2v
6: 0.757v
8: 3.3v
13: 3.3v
16: 12.6v
17: 5v

So PP5V_S5 has returned.

 

[hambook]

Just to check my understanding so far. U7200 needs Pin 6 to be low, Pin 13 to be high, and 13/17 to be at 3.3v and 5v. So this chip is now functioning correctly?

 

[2informaticos]

"U7200 needs Pin 6 to be low"
Don't make wrong assumptions so easy!
However, 0.757V is the correct voltage there; theoretical value is 10uAx78.7Kohm=0.787V.
Chip's datasheet explains why.

You should now have 3V3_S5 present at L7220.

 

[hambook]

I do now have 3V3_S5 present at L7220. I don't have PP5V_S3 though. PM_SLP_S4_L is 0v. C1802/1803 are 3.3v

 

[hambook]

Update: After reading some forum posts, I replaced U2600 on a hunch. I now get consistent green light.

PP5V_S3: 3.3V
PM_SLP_S4_L: 3.3V

Power supply is drawing 0.226A. No fan spin.

 

[2informaticos]

PM_SLP_S3_L should be also high.
Check that, as all voltages controlled by this signal too.

 

[hambook]

Looks like PM_SLP_S3_L is also 3.3v

 

[2informaticos]

Then you should have voltage in many S3 and S0 power rails; not CPU maybe.
ALL_SYS_PWRGD goes high?

 

[hambook]

Looks like ALL_SYS_PWRGD is still low. Will do some backtracking and see what rails I'm missing

 

[2informaticos]

Remove Q7950 and check ALL_SYS_PWRGD again.

 

[hambook]

ALL_SYS_PWRGD still low (0.027v) with Q7950 removed.

 

[hambook]

Q7950
1: 0.033V
5: 1.075V
6: 3.29V
7: 1.505V

Also noticing now that the PCH gets hot after sitting plugged in for 5 or so mins. I take it that's not good...