A2251 820-01949 no power

[hgoncalves]

Hi,

I have an A2251 that has no power.

It puls 5V and 0.120A from lab PSU.

It had PP3V3_G3H shorted, and after replacing U6903 that short is gone.

However on PP2V5_NAND_SSD0 I have 0V and 0.095 on diode reading wich I think is to low (not sure).

Already tried DFU but it isen't recognized.

Can you help?

 

[2informaticos]

You definitelly have a problem with 2V5 power supply for SSD.
Lift L9080/81 and check where the bad reading remains.
I suspect at least one dead NAND chip there.

Please, use correct line names.
What relation do you see between U6903 and 3V3_G3H???

 

[hgoncalves]

Sorry. I ,meant to say PP3V3_G3H_RTC_REG_R.

After Lifting both L9080/81, the diode reading seams to became normal (0.396).

However, now PPBUS_G3H droped to 10.40V, and osclitaes until reaches 12.27V

PP1V8_G3S = 0V
PP3V3_S5 = 0V
PP5V_G3S = 0V
PP3V3_G3S = 0V

 

[2informaticos]

"diode reading seams to became normal"
Yeah, which side of the coils???

 

[hgoncalves]

Both sides were normal.

PP2V5_NAND_SSD0 was 0.396 and the other sides were above 0.400 on both coils. Shall I remove the coils to give exact measured?

 

[2informaticos]

You've said to have 0.095 before.
This low reading should remain one side of the coils.
You must lift both coils and check.

 

[hgoncalves]

Hi.

Yes I had 0.095 on PP2V5_NAND_SSD0, but I might have made the mistake that haven't waited enough before the mesure, because now, after powering on the board, i still get that value there for several minutes after powering off. Sorry.

I lifted again both coils and I have:

L9080:
1 = 0.518
2 = 0.396

L9081:
1= 0.523
2 =0.398

 

[2informaticos]

So you get 0.092 reading only for short time, after power is removed?

Do you get correct 3V3_G3H_RTC now (stable)?
What about SLPS2R and AWAKE voltages of T2?

 

[hgoncalves]

Hi, yes thats correct. On PP2V5_NAND_SSD0 I get 0.95 for a few minutes and growing until reaches 0.398.

3V3_G3H_RTC = 3.395 stable

PP0V8_SLPS2R = 0V
PP1V1_SLPS2R = 0V
PP1V8_SLPS2R = 0V

PP1V2_AWAKE = 0V
PP1V8_AWAKE = 0V
PP3V3_AWAKE = 0V

 

[2informaticos]

Check U7800's LDOs.

 

[hgoncalves]

U7800:
LDO_CORE = 1.491V
PMU_LDO3_OUT = 1.834V
LDO_RTC = 1.481V

PP3V_G3H_RTC = 0.052V

 

[2informaticos]

What about LDO0/2?

Be sure R7900 is good (0 ohm).

 

[hgoncalves]

LDO 0 = PP0V8_SLPS2R = 0V
LDO 2 = PP1V2_AWAKE = 0V

R7900 = 0.1 ohm

 

[2informaticos]

Check diode mode to ground on missing LDOs.
If good, change U7800.

 

[hgoncalves]

Diode reading:
PP0V8_SLPS2R = 0.238
PP1V2_AWAKE = 0.535

I don't have other board to compare. PP0V8_SLPS2R is a bit low, correct?

 

[hgoncalves]

Hi,

After replacing U7800, now I also have LDO 0/2, but the mac is rebooting.

It puls 5V, and reaches 130mA and then reboots.

Shall I try DFU?

 

[2informaticos]

Check if you can put in DFU.

 

[hgoncalves]

How can I force DFU on this board? Can you help?

 

[2informaticos]

You can use RE032 pads.
Connect a switch there.

 

[hgoncalves]

Hi. Thanks!

Force DFU didn't work. DFU isen't recogized.