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Old 01-22-2022, 04:30 AM   #1
ex250
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Default Imac A1311 late 2009 820-2494A

Hello guys, I have this one with a non-starting failure, on board diagnostic led 1 lights ok, tested other know working power supply to discard, same behavior.

The board is the 820-2494A

the S5 lines read:

PP1V1_S5_REG -> 1.11V

PP3V3_S5_REG -> 3.37V

PP5V_S5_LDO -> 4.98V

PP12V_S5 -> 12.01V

Seems all ok

This ones not, too high readings, maybe the same culprit:

PGOOD_1V1_S5 -> 3.37V (should be 1.1V?)
5VREG_EN -> 3.37 (should be 5V?)

I was thinking that the U7300 could be the problem, but replaced and all is the same.

Any one could point me some direction? Quite lost with these boards.

Thanks!
Attached Files
File Type: pdf LB# 820-2494 schematic diagram.pdf (1.60 MB, 7 views)
File Type: zip LB# 820-2494 ''Board View'' file.zip (82.4 KB, 6 views)

Last edited by ex250; 01-22-2022 at 04:33 AM..
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Old 01-23-2022, 03:01 AM   #2
ex250
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Default Re: Imac A1311 late 2009 820-2494A non starting help

No body?
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Old 01-29-2022, 01:23 AM   #3
reformatt
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Default Re: Imac A1311 late 2009 820-2494A

The 2nd LED on these only comes up when PP3V3_S3 is on, which in turn is enabled from PM_SLP_S4_L. You need to go through the pre-requisites for this signal to be generated from the PCH.

Whilst this is doable, troubleshooting these boards outside of the iMac requires a jig of some nature. Is supplying 12V to the main power input enough from a bench supply? Maybe, but given the age of these things now, I refuse to fix mainboard faults on them.
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Old 03-20-2022, 06:04 AM   #4
ex250
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Default Re: Imac A1311 late 2009 820-2494A

Sorry for the delay, quite lost on this board. The 12 V supply is ok, tested with 2 different know working power supplies.
It's not quite clear for me how to check PM_SLP_S4_L
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