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Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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Can anyone tell me what these PSU pin abbreviations mean? PSU 614-0446

Hi all. I’ve gutted a 27” iMac that suffered the near-universal GPU failure, and I’m converting it into a monitor with a cheap LCD-driver board from eBay. Instead of a likewise cheapo PSU and inverter, I’m trying to use the original Apple ones. I found a pinout of the PSU’s output connector, but don’t know what some of the abbreviations mean or their function. Can anyone help? I don’t have the motherboard to trace anything back to, so that’s not an option.

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Update (07/27/2020)

Well, I got the whole thing working. I ran a switch to ground the PS_ON line as required, which activates the stock PSU. The PSU has several 12V outputs, so one of them powers the LCD driver board, another goes through a converter to provide 5V to the backlight-on signal, and another gets converted to 3.3V for a PWM module to control the backlight brightness at 150 kHz.

The LCD driver board had its own power supply for the backlight, but some reviews said it asn’t as bright as the stock one so I added the PWM module to drive the stock one.

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Hi. Could you elaborate on how you got the builtin inverter working? I'm trying to do the same by converting my imac to a display.

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Hey, could you please explain how did you connect and which PWM module did you use? I'm trying to achieve the same

Thanks!

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Could you please elaborate how you got the original inverter running? I have started converting my 2009 27" iMac to a monitor with one of the controller boards from eBay/AliExpress and while it does work I would very much prefer using the original inverter.

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The only lines that you can use is the PP12V & GND pins (3 + & 5 - pins) 12 Volts + and -

PS ON is the power switch line with shorts to GND to enable the power supply (soft on)

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Great, thanks! I'll use one of the PP12V to power the controller board. The (momentary) power switch is still intact, so if I connect one lead of it to ground and the other to PS_ON it will function as an on/off switch?

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Just tap the power switch leads

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The power switch is just a switch with two wires dangling at this point. So I conclude that I should run one wire to ground and the other to the PS_ON connection.

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Its a bit more than that! It's a soft power button not a AC power switch. It uses a momentary contact which is using a low voltage which it then alters the higher voltage via a MOSFET power transistor.

I think you really need to review the system schematics to understand the logic here board # 820-2828, 2011 27" iMac A1312

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Thanks Dan. I understand that it's triggering some kind of relay-like switching of higher voltage. I don't have the schematics. I guess for now I just need to know how to power up and down the PSU to get this thing functioning as a monitor, which I'd prefer to do with the original power switch.

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I used this solution to start/stop the power supply from the button without locking, using

original power button.

K561LE5 (analog CD4001A) + mosfet IRF3205

C - 0,1 , R1 - 10k, R and R2 - 100k

Use U+ from PP12V_G3H_ACDC, mosfet connect drain to PS_ON

It is work fine

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Thanks, Andrey! I can confirm this circuit works perfectly.

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If you left the main board power cable connected to power supply, here are the useful pins on the 14-pin connector. 12V always on is same as G3H_ACDC. Hook up Andrey’s switch circuit to pins 2,4, 14 (arrows).

Anyone know if it is safe to gang the 12V switched outputs for more current?

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Andrey’s circuit from above

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