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Hello guys,
I have a dead iMac with no LED on at all.
Logic board ID 820-3588, power supply tested OK
power input to power supply OK
tested with new known good power supply
but still no 12v present on logic board.
any advice for this case?
Update :
Tested with normal board and works fine. so the problem is the logic board. Power supply output 0v with original logic board
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Where are you testing for 12V? That might help determine exactly what's going on. It's possible the connector for the power supply is at fault.
The first LED is reliant on 12 volts insomuch as all other voltages are derived from it. The first LED is actually lights from PP3V3_S5, which still leaves some other things in the logic board chain that could be at fault even beyond the 12V.
这个答案有帮助吗？
I check J6900 and all pins 0v. is it possible that connector is damage?
@fianz123 You're using the bits of the connector that come through to the front of the logic board? If yes, and you're not getting any voltage, then I would say it's possible the issue is the connector.
I would make sure the pins inside the connector are present. I don't recall exactly how those connectors are laid out, but I expect its similar to most other molex style connectors. Also make sure there is continuity between the pins in the connector and the solder points where you've been measuring for voltage on the logic board.
Just for point of reference, the top 3 should be ground, and the bottom 3 would be 12V.
@flannelist My English is not good so I can't explain in long sentences. continuity is ok but still no 12v on that point and no 12v output on power supply side. so it's not the connector. power supply not create 12v when connected to logic board
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