820-00034-A not turning on

BCN_Techs

Member
Hi guys,

I have iMac 21,5 820-00034-A logic board that doesnt turn on.

1st led is on.

G3 Rails are present,

PP12V_S5, PP5V_S5, PP3V_S5 are presents too.

ALL_SYS_PWRGD is 0V ( i have anothet working Mac with same board and ALL_SYS good is also 0V in S5)


Any idea? What else i have to meausure. Tried SMC bypass not running.



P.S: PM_SLP_S5_L is present 3.3V
 
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2informaticos

Administrator
Staff member
"PM_SLP_S5_L is present 3.3V"
Then all S4 voltages should be present too; confirm that.
If not, check for short at all S4 power rails; especially L7650.
 

BCN_Techs

Member
Also there is something happening that i have discovered just now. When plug cable iMac is entering s0 state, but no fan spins and only first led is on When press and hold power button for few seconds all s0 rails back to 0V again. The only rail missing is PP1V5_S0 ( not shorted to ground.
 
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BCN_Techs

Member
U7490

Pin 1,2,3,5 are 0V Pin 4 is 3.2 and Pin 6 1,8.

U8440 board doesnt have it. I can see it in pdf too, but there is no componenten U8440 on it.


P.S: U6200 was getting very hot. I removed it for now. Do you thinkg it can make machine not to turn on?
 
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2informaticos

Administrator
Staff member
U8440 pads look untouched?
It wasn't ripped off?
C8440 is there?
Do you get P3V3_S0_FET output voltage?

Check for short (or low value) at C6203.
Board should start if R6200 removed.
 

BCN_Techs

Member
No informaticos, there is just no pads. Will attach photo tomorrow. It's strange because it's not "NO STUFF" just there is no componentes and pads there. WIll check all u wrote tomorrow. Thank you
 

2informaticos

Administrator
Staff member
So the board doesn't correspond with schematic.

What about the other things mentioned in my previous post?
 

BCN_Techs

Member
sure, will do it tomorrow as promised:) thanks

P.S: at least in pdf there is 820-0034 mentioned in text so it's very strange
 

BCN_Techs

Member
So i have checked and:

it wasnt ripped off

there is no C8440

C6203 has low resistance to ground 120 OHMS ( checked with working logic board and it must have about 120Khoms).

There is no R6200. If you mean U6200 the board doesnt start with that removed.


Also U8400 seems to be blown. Dont have donor board so will wait untill it arrives me from China. Will back once put it again. Thank you 2Informaticos.
 

BCN_Techs

Member
I have recieved the U8400 and changed it. Again got 1.5V on PP4V5_AUDIO_ANALOG and almost shorted with 100 Ohms resistance to ground. Checked all and finally removed U6201 now get 4.5 instead of 1.5V and resistance to ground is ok. The question is, will iMac turn on without U6201?
 

BCN_Techs

Member
PP3V3_G3 - 3.3V
PP12V is ok
PP3V42_G3H - 3.4V

PP12V_S5 - 12V
PP5V_S5 - 5V
PP3V3_S5 - 3.3V


PP5V_S4 -5V
PP3V3_S4 3.3V

PP1V8_S3 - 1.8V
PP1V2_S3 - 1.19V

The board is going to S0 state ( but only first led on it is on). So


PP12V_S0 - 12V
PP5V_S0 - 5V


PP1V5_S0 - 0V and nod shorted to ground. Checking line there is nothing wrong i can see using microscope It's not generated because of U8440 doesnt sent enable signal to U7490. The problem is that schematic and boardview i have there is no U8400 on real board. Already checked all avialable on internet and all are same.

P.S. I Found it. it's on the other side of the board near where it must be on boardview. If someone in the future check schematic will need this info. Now will continue checking.
 
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BCN_Techs

Member
Measermunt are done with board in S0 state because when i connect power it enters in that state automaticly.


U8440:

1 - 3.3 V
2 - 5V
3- 0V
4- GND
5 - 3.3V
6 - 0V
7 . 3.3V
8 - 3.3V

U7490

1,2,3 - 0V
4 - 3.3V
5 - 0V
6 - 1.8V


Pin 3 of U7490 is what make me think that U8440 is bad ( i was wrong in my previous post it was U8440 changed
 

BCN_Techs

Member
Solved. It was PP3V_S0 low value due U8400. Changed not it seems to work. Will assemble it tomorrow and confirm. Thanks
 
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