iMac A1312 820-2828-A only led one lit

[bellyacres]

I'm stuck staring at the schematic.

PP12V_G3H is 12.02
PP3V42_G3H_REG measured on the output of L7900 is 3.38. The schematic indicates that is should be at 3.425. I'm not sure if that is causing my problem or not. Somewhere I have it in memory that it needs to be 3.425.

I have 3.39 at the power button also.

Any pointers most welcome.

Thanks

Using the schematic and boardview from this post.
https://www.badcaps.net/forum/showth...ght=820-2828-a

[qonma]

Re: iMac A1312 820-2828-A only led one lit

I'm stuck staring at the schematic.

PP12V_G3H is 12.02
PP3V42_G3H_REG measured on the output of L7900 is 3.38. The schematic indicates that is should be at 3.425. I'm not sure if that is causing my problem or not. Somewhere I have it in memory that it needs to be 3.425.

I have 3.39 at the power button also.

Any pointers most welcome.

Thanks

Using the schematic and boardview from this post.
https://www.badcaps.net/forum/showth...ght=820-2828-a

cek the pin, sometimes corotion, or soldering not conected with the board

[piernov]

Re: iMac A1312 820-2828-A only led one lit

3.38V should be fine. Make sure the power button is working, if possible try another PSU, and go through the list of power rails to see what's present/missing. (G3H→S5→S3→S0)

[bellyacres]

Re: iMac A1312 820-2828-A only led one lit

3.38V should be fine. Make sure the power button is working, if possible try another PSU, and go through the list of power rails to see what's present/missing. (G3H→S5→S3→S0)

Power button is testing fine. I've got the PSU and MB out of the machine anyway. The solder looks fine in the connector. I've just been shorting the two pins together, not using the actual power button.

I don't have another PSU. On the MB, connector J600 the only voltage present is pin 11 at 12.09, and pin 13 at 4.29.

Q610 has the 4.29 on ping 3, I believe that pin 1 (PM_EN_P12V_SO_FET) should get 12v to turn on the PSU. I have 0v on that pin regardless of the power button state.

I'm clueless on where exactly to test for S5, S3, S0...
Unless I've totally missed it the 12.09 is G3H. Yes?

[guzq]

Re: iMac A1312 820-2828-A only led one lit



Power button is testing fine. I've got the PSU and MB out of the machine anyway. The solder looks fine in the connector. I've just been shorting the two pins together, not using the actual power button.

I don't have another PSU. On the MB, connector J600 the only voltage present is pin 11 at 12.09, and pin 13 at 4.29.

Q610 has the 4.29 on ping 3, I believe that pin 1 (PM_EN_P12V_SO_FET) should get 12v to turn on the PSU. I have 0v on that pin regardless of the power button state.

I'm clueless on where exactly to test for S5, S3, S0...
Unless I've totally missed it the 12.09 is G3H. Yes?

Hey bellyacres,

Did you solve this issues ?

I've same issues but Q610 pin 3 = 0v
I got 1 LED lit, checked all power rails from S5 to S0 all present

R501 pin 1 = 3.3v / pin 2 = 1.8v
R502 pin 1 = 3.3v / pin 2 = 3.3v
R503 pin 1 = 3.3v / pin 2 = 3.3v
R504 pin 1 = 3.3v / pin 2 = 3.3v

[mon2]

Hi. This thread should be in the desktop forum.

Sounds like a bad gpu.

https://www.ifixit.com/Answers/View/...+LED+1+present