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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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Switching the inverter on without the logic board

So my 27” i7 iMac has the famous GPU issue, and I wasn’t one of the lucky ones who had their boards replaced by Apple. After a long period of feeling disgruntled, I finally came to terms with it and successfully turned it into an external display for my MacBook Pro via a 3rd party LCD driver board.

It works great except the supplied inverter is not powerful enough so the backlight is only about half as bright as it was with the original inverter, as explained by the board supplier.

That got my thinking though. I’m using the original PSU board to supply 12V to the new board and inverter via the ‘always on 12V’ rail. And the original inverter is still installed and connected. Potentially all i’d need to do is reconnect the original inverter to the display and supply an ‘on’ signal to it somehow from the new board. The board supplier said there are a couple of places I can get a +5V on source from the new driver board, if that is indeed what is required.

Does anyone know what the PSU and inverter need signal wise (usually from logic board) to switch on? High? Low? What voltage and on what pin(s) ?

Thanks.

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I’m also trying to use the APPLE backlight Inverter Bd instead of the CHINA Backlight Inverter bd to solve the BRIGHTNESS issue. Still working on it!

On PWM signal, I just used 3v DCin (I ordered a PWM generator to supply 13kHz, 3V, but not received yet. Not sure why I am only getting 12.51 Vout when using the APPLE backlight inverter bd. I suspect either EN or PWM is why I am only getting on 12.51 Vout CN2.1

BE CAREFUL - DANGER HIGH VOLTAGE.

Here’s the Voltage measurements I took.

LCD - NO BACKLIGHT

iMac with Apple Inverter, no PSU and no LogicBoard

INVERTER VOLTAGES

  • Vout 12.51V (CN2.1)
  • Vin 12.58v (CN1.2)
  • ENA 3.22v (CN1.1)
  • PWM 3.02v (CN1.3)

LCD - BRIGHTNESS LOW (iMac as MONITOR using China Inverter/Driver/Controller)

CA-255 China Inverter board

iMac with China inverter, no PSU and no LogicBoard

INVERTER VOLTAGES

  • Vout 32.5v (CN4.1)
  • Vout 87.6v (CN4.1) with LCD disconnected
  • Vin 11.93v (CN1.1)
  • ENA 4.64v (CN1.3)
  • PWM 0v (CN1.4)

LCD -BRIGHTNESS EXCELLENT (Normal 2011 iMac EMC2429)

iMac with Apple inverter, PSU and LogicBoard (normal 2011 iMac EMC2429)

INVERTER VOLTAGES

  • Vout 36.5v (CN2.1)
  • Vin 11.8v (CN1.2)
  • ENA 3.22v (CN1.1)
  • PWM 3.08v (CN1.3)

Block Image

I am using Yeeco USB Power Supply for the 3v PWM and 3.25v ENA

https://www.amazon.com/dp/B07VDRM4PG?psc...

I am using 12V/10A adapter for the Vin 12V to the Inverter board

Update (06/18/2021)

OK, I tried to use three 12V adapters as follows.

  1. 12V/10A adapter into Apple backlight inverter board
  2. 12V/5A adapter into HDMI driver board
  3. 12V/5A adapter into CIG. lighter to USB that power two Yeeco USB Step Down Power Supplies and one Yeeco is set to 3.3V to supply the EN signal, the other Yeeco is set to 3.3V to supply the XY-KPWM signal generator for the 13kHz 3.3V signal for PWM

So the Apple backlight inverter board has the 12Vin , 3.3V on EN, 3.3V/13kHz on PWM

GND for the 12Vin is connector to the 12V adapter , GND for PWM / EN is wire from screw hole on backlight to signal generator and Yeeco.

I plugged in 12V adapter for Apple backlight first, then 12V adapter for HDMI driver next, then 12V adapter for USB step down last and the LCD screen comes on for about a second with the image, but then goes to BLACK.

Not sure what to do next?

Update (06/18/2021)

ok,

I swapped the inverter board between working 2011 iMac machine and the iMac “Monitor”

the 2011 iMac machine still works great, LCD lights up and works.

the iMac “Monitor” has the same condition, where the LCD lights up with correct image for only 1-2 seconds , then goes black.

so LCD is good, Inverter bd is good

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I measure this on the iMac “Monitor”, so boost circuit not working for some reason…

Vin 12.96v

PWM 3.09v /97% duty cycle

EN 3.27v

Vout 12.89v

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