820-00928 stuck on 5v

Hello. I am usually pretty good at fixing 5v issues on touchbar machines, but this one has got me stumped. This board had very minor liquid damage in some small areas around the board. It takes steady 5v on all 4 ports and the amp draw fluctuates between 40-60ma. U3100 has some minor corrosion around it so I changed it but it did not make any difference. I do not find any shorts and PP3V3_G3H is present at 3.4v on all 4 ports. I compared diode mode reading on all the LDO lines for the CD3215 and they all match. All 4 chips produce their 1.1v LDO rail, so it does not seem to be an issue with the CD3215's. Despite this, I still replaced the other 3 CD3215's just in case but still have the same issue. I figured it must be an SMC issue, so I replaced the SMC from a donor board of the same model, but still same thing. All 4 ports still steady 5v and 40-60ma. SMC_RESET_L and BUF_SMC_RESET_L are both preset at 3.3v and PPBUS_G3H is ~10mv and is not shorted, so I don't know what else could be wrong. Is there something else I should check?
 

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There should be other components affected by corrosion.
Remove F7000/1 and check C7050 voltage.
Check ohm resistance over C7020/23.
Also check R/C/Q7030/40.
 
There was only some minor corrosion around U3100, U9391/93 and C7608. I removed F7000/1 and I get about 75mv on c7050. C7020/23 are both 3.3 ohms. I also replaced U7000 just in case, but no change. R/C/Q7030/40 seem to all be ok. All 4 ports still takes 5v and amps cycle between 40-60ma. One thing I did notice is that when its using only 40ma, SMBUS_SMC_4_G3H_SCL and SMBUS_SMC_4_G3H_SDA are 3.4v. Then when it goes to 60ma, both of those voltages drop to around 0.5-0.8v, then go back to 3.4v when the board goes back to 40ma current draw.
 

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Post voltage and diode mode to ground at SMBUS_SMC_5_G3H_SCL /SDA lines.
Check PPBUS_G3H and 3V3_G3H with battery connected; w/ and w/o charger present.
Don't forget to connect battery data cable.
 
SMBUS_SMC_G3_SCL and SMBUS_SMC_G3_SDA are both 3.3v and fluctuates down to about 2.6v every couple of seconds. Both measure 0.441 in diode mode, which matches another board I have that gets 20v. PPBUS is like 5mv with or without the battery connected and PP3V3_G3H is 3.4v with the battery and charger, but 1.4mv with just the battery. I don't think the battery is charged though so that would be why PP3V3_G3H is missing on battery alone.
 

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Can you charge the battery with the other board, which switch to 20V?
This may help to diagnose if the problem is on USB-C side, or other side.
 
Yea I was able to charge the battery using another board with a dead CPU. Now when I connect this board to the charged battery and connect the charger, I get 20v 0.00a, still does not turn on. PPBUS is 12.7v and PP3v3_g3h is 3.4v with both the battery and charger connected and its the same thing with just the battery.
 

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If USB-C ports switch to 20V with battery connected, means SMC can communicate properly with CD3215 chips.
You can have a problem with U7000, or its surrounding components.
Check SMC_BC_ACOK and A/BMON.
 
SMC_BC_ACOK is 3.4v but AMON and BMON are 0v both with and without the battery connected. I replaced U7000 again, but still the same
 

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SMC_DCIN_VSENSE is correct, as you don't get 20V input voltage yet.
A/BMON are also good, because the board doesn't start.

Check power on signals with charger plus battery connected.
 
SMC_BC_ACOK is actually 3.4v only when just the charger is connected and the board is stuck at 5v. When the battery and charger are connected and its taking 20v, that signal is 0v. I checked the below signals with just the charger connected and then again with both charger and battery connected.

SignalBattery + Charger
(20v)
Charger only
(5v)
SMC_USBC_INT_L00
SMC_CHGR_INT_L3.40
SMC_PMIC_INT_L3.43.3
SMC_BC_ACOK03.4
SMC_ADAPTER_EN00
S5_PWRGD00
PM_BATLOW_L078.7mv
PM_DSW_PWRGD00
SMC_RESET_L3.43.4
PM_RSMRST_L0360mv
 

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You should get some voltage on PPBUS_G3H, when battery is connected.
Be sure to get good contacts with data cable.
Also try another battery.
If not possible, then you have a problem with the communicayion between SMC, U7000 and battery.
 
PP3V3_S5 - 0v
PP5V_S5 - 0v
PP5V_S4 - 0v
PP3V0_G3H - 3.09v
PM_DSW_PWRGD - 0v
PCH_INTRUDER_L - 2.8v
RTC_RESET_L - 3.08v
PCH_SRTCRST_L - 3.4v
PPDCPRTC_PCH - 1.123v
SMC_PMIC_INT_L - 3.4v
PM_SLP_SUS_L - 0v
LPC_PWRDWN_L - 26.5mv
PM_RSMRST_L - 0v
PM_PCH_PWROK - 0v
PM_PCH_SYS_PWROK - 0v
PMIC_SHUTDOWN_L - 3.2v
 

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Check LDO and VREF rails at U7800 (7 OF 10).
Also check SMC_ONOFF_L and SMC_RESET_L levels.
Remember to keep battery connected.
 
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