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820-00840-A A1708 20V 0A no PPBUS_G3H

J

jadao

Member
This board was liquid damage with 5V 0A. Corrosion at cd3215 and nearby, also the PI3USB32 chip (the one we don't see on schematic &brdvw) was corroded.
Reflowed both of them and replaced all resistors around both CD32s.

Now I get 20v 0A and ppbus_g3h 0V with no short (diode mode 0,410)
Replaced u7000 and Q7030/40 and it's the same (20V 0A).

At U7000
Aux_det 5v
R7020/21/61/62 are ok
TBA_HPWR_EN_L 3.4V
PM_EN_P3V3_G3H 5V
SMC_RESET_R_L / SMC_RESET_R 3.4V
SMC_CHGR_INT_L 3.4V
CHGR_ACOK 3,3V
SMC_RST_IN 0V
PD_SMC_CBC_ON 0V

I don't know if even I get 20V I still need to check again near CD32 or even replace them, or something related with SMC?
Don't know what to check anymore at this point.
 
2informaticos

2informaticos

Administrator
Staff member
CD3215 chips should be good now, if switch to 20V.
Check other U7000 voltages; VDDA/P, VR1_3P3, A/BMON.
Compare diode mode readings on secondary power supplies with good board.
 
J

jadao

Member
Oh forgot to post other u7000 voltages:
R7075 is 5ohms and VDDA/VDDP is 5V
VR1_3P3 is 3.3V
A/BMON are both 0V / 0V (char only) with working board I get 0,050V / 0V (charger only)
TBA_COMP is 1.1V noticed it was 1,6 and 1,5V on working board

I compared diode mode reading with a working board and I found that
L7900 and L8060 are respectively 0.041 and 0.048 on the patient board as opposed to 0.245 and 0.206 on the working board...

Can I remove the coils, check from where the short is comming and eventually disconnect the feedbacks and see what happen when I plug power?
 
2informaticos

2informaticos

Administrator
Staff member
Not really short, but very low values comparing with good board.
Is sufficient to lift the coils one side; no need to use hot air.
Then check where the low values come from.
 
J

jadao

Member
I lifted the coils on one side and found the low values coming from PP1V_S5G and PPVCCPCH_S5G...:(
Removed also the feedback resistor going back to the u7800, but the low diode mode values are still present.
I started to isolate components on the PPVCCPCH_S5G path (only few caps on this rail) and I can confirm the low diode mode value is coming from U0500. Maybe some crap under the cpu but I think it's a hopeless extremely sensistive fragile board...
 
2informaticos

2informaticos

Administrator
Staff member
Nothing to lose trying to burn eventually crap.
Heat CPU until 180-200 degrees for 15-20s.
Use quality flux, not chinese honey...
 
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