A2681 no power

[2try’s]

Hi, i have a 820-02536-09 board that not powering on. I have already found a shorted to ground cd3217b13 (it was shorted UF400 on PD_UPC0_USBP3_RN rail)
After changing this chip from the same donor motherboard it started showing 0.722 diode mode but still no power. Usb-c tester showing 5v and different pulsing on each connector, but both between 30-218 mA

 

[2informaticos]

Steady 5V on the input?
What about PPBUS_AON and 3V8_AON?

 

[2try’s]

5v steady
PPBUS_AON - 12.32v, not steady, dropping to 12.03v, to 0v and then back to 12.32v
PP3V8_AON - 3.789-3.801v

 

[2informaticos]

Remove F5200 and check if C5252 voltage is stable.

 

[2try’s]

Removed f5200
c5252 - 12.32v stable

 

[2informaticos]

Resolder it.

Now check diode mode to ground on all secondary power rails.
Also check voltage and diode mode on U8100 and U7700 LDOs; pages 39 & 34.

 

[2try’s]

PP3V8_AON - 0.310
PP3V3_AON - 0.499
PP1V8_AON - 0.370
PP5V_S2 - 0.286
PP3V3_S2 - 0.461
PP1V8_S2 - 0.247
PP1V8_S2SW - 0.384

U7700 LDOs
PP1V25_S2 - 0.249
PP0V72_S2_VDD_LOW - 0.253
PP1V8_AON_SPMU - 0.557
PP1V2_AON_SPMU - 0.571
PP0V78_S1_VDD_FIXED - 0.252
PP1V5_LDOINT_SPMU - 0.255

U8100 LDOs
PPVDD_LDO20_14_8_3 - 0.251
PP1V8_AON - 0.375
PP1V8_AON_MPMU - 0.479
PP0V855_S2SW_CIO - 0.241
PP1V5_LDOINT_MPMU - 0.254
PP1V05_S2SW_VDD2H - 0.034
PP3V3_S2_LDO - 0.453
PP1V2_AON_MPMU - 0.251
PP3V3_S2SW_SNS - 0.708
PP1V2_AWAKE_PLL - 0.413
PP3V3_AON - 0.499
PP1V2_S2_CIO - 0.457

 

[2informaticos]

U8100 & U7700 have also many buck converters.
These are also considered secondary power rails.

 

[2try’s]

you talk about buck rails on page 33 & 38?

 

[2informaticos]

Exactly...

 

[2try’s]

U8100
BUCK3_LX - 0.251
BUCK3_FB - 0.251
BUCK4_LX0 - 0.035
BUCK4_LX1 - 0.035
BUCK4_LX2 - 0.035
BUCK4_FB - 0.035
BUCK7_LX0 - 0.238
BUCK7_LX1 - 0.238
BUCK7_FB - 0.238
BUCK9_LX0 - 0.238
BUCK9_LX1 - 0.239
BUCK9_FB - 0.239
BUCK11_LX0 - 0.203
BUCK11_LX1 - 0.203
BUCK11_FB - 0.203
BUCK13_LX - 0.251
BUCK13_FB - 0.251

U7700
BUCK5_LX0 - 0.242
BUCK5_LX1 - 0.242
BUCK5_FB - 0.242
PP2V58_AWAKE_NAND_VCC - 0.309
BUCK6_LX - 0.309
BUCK6_FB - 0.309
BUCK8_LX0 - 0.184
BUCK8_LX1 - 0.184
BUCK8_LX2 - 0.184
BUCK8_FB - 0.184
BUCK10_LX - 0.108
BUCK10_FB - 0.108
BUCK12_LX - 0.319
BUCK12_FB - 0.319
BUCK14_LX - 0.423
BUCK14_FB - 0.423

 

[2informaticos]

Check if you can put the board in DFU.

 

[2try’s]

No, it can’t go into dfu

 

[2informaticos]

Did you try with battery connected?
PPBUS_AON still droping to 0V?

 

[2try’s]

With battery connected tester shows pulsing between 5-448 mA
PPBUS_AON still pulsing, but dropping to 9.9v instead of 0v

 

[2informaticos]

3V8_AON and LDOs voltages are stable then?

 

[2try’s]

yes, they are stable

 

[2informaticos]

Then the machine should appear into DFU.

 

[2try’s]

Maybe I am doing something wrong, you talk about getting board into DFU using Apple Configurator?

 

[2informaticos]

Of course; it should be detected.