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

EARLIER YOU SAID “Next the backlight LED power cable. I didn’t measure it because I didn’t want to disconnect it from the LCD, but it looks functional and I doubt that at least three wires fail at exactly the same time (since it supplies three groups of LEDs with power).” I would measure the Voltage at the Backlight Vout pin. you indicated you are getting 12Vin, but what voltage are you getting on Vout? the backlight board should be boosting the voltage to like 3x the voltage to like 36Vout. I am having a similar issue where I have 12Vin to backlight and 12Vout of backlight, so NO boost on the voltage. I am trying to test the backlight board outside the iMac by supplying 12Vin,3.3V-EN,3.3-PWM with the result being 12Vout, with no BOOST to 36V and am also getting NO LCD lighting. I know the LCD works cuz I used a China backlight and it works except no adjustment to brightness issue I am having. hope this helps

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 (1) Vout 12.51V (CN2.1) (2) Vin 12.58v (CN1.2) (3) ENA 3.22v (CN1.1) (4) 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 (1) Vout 32.5v (CN4.1) (2) Vout 87.6v (CN4.1) with LCD disconnected (3) Vin 11.93v (CN1.1) (4) ENA 4.64v (CN1.3) (5) PWM 0v (CN1.4) LCD -BRIGHTNESS EXCELLENT (Normal 2011 iMac...

I am 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. Here are Voltage measurement I took. Be CAREFUL - DANGER HIGH VOLTAGE. LCD - NO BACKLIGHT 3.) 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 2.) 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...

I found the attached "Current Adjustment Guide" on alibaba my Backlight Inverter Board has the following weld on RC3,RC4,RC5,RC6,RC7 NO weld on RC1,RC2 R10 has 1R00 resistor R11 has 2R00 resistor https://www.alibaba.com/product-detail/CA-255S-10-48-inch-LED_62067468081.html

I notice the LCD brightness is low. Why does PWM signal go from 3V to 0V when you turn LCD on?? I checked the voltages on both the Original Apple Backlight Inverter board and the new Chinese Backlight Inverter board. Chinese INVERTER BOARD LCD on pin 1 11.45V pin 2 11.45V pin 3 4.53V (on/off) EN pin 4 0V (pwm) pin 5 GND pin 6 GND Chinese Inverter board LCD off pin 1 12.18V pin 2 12.18V pin 3 0V (on/off) EN pin 4 3.0V (pwm) pin 5 GND pin 6 GND APPLE INVERTER BOARD LCD on pin 1 3.25V (on/off) EN pin 2 12V pin 3 2.88V pwm pin 4 GND pin 5 12V pin 6 GND

per Apple Technical Specification, your iMac 2019 3.0Ghz is configurable to 32GB MAX https://support.apple.com/kb/SP790?local... Did you try 64GB?

I bought these 8 ohm/5W speakers on ebay, since the seller of the LCD controller board said they would work. I plugged in and they did NOT work. I checked the pinout and then swapped the black and read wires and plugged in and they did NOT work. http://www.vslcd.com/Specification/M.NT6... https://www.ebay.com/itm/1-Pair-8-ohms-5W-Audio-Speaker-Amplifier-For-Universal-LCD-Controller-Board-New/182085971437?ssPageName=STRK%3AMEBID...

here is the PINOUT for the Speaker Connectors on Logic board 820-2828 Update (06/21/2020): here is picture Update (06/21/2020): Dear friend, Thank you very much for your great news. About speaker, sorry that it can not support the original iMAC speakers . As it can not provide enough power. But it can support the 5W 8ohm speaker instead. Will this give you the answer? Hope you enjoy shopping with us all the time. Have a great day!

Did you use this Driver Board? https://www.ebay.com/p/12015167280 I have an empty chassis of the iMAC EMC 2429 except for Left/right speakers. I installed the Driver Board kit and hooked everything up and it now works as a monitor via HDMI. I notice the Driver Board has Speaker Output and what looks like a 3.5mm connector for AUDIO. HOW DID YOU CONNECT THE INTERNAL IMAC SPEAKERS TO THIS DRIVER BOARD?? Update (06/21/2020): btw, How did you Power the Driver Board, I used a 12V/5A supply and notice this Power Supply gets pretty HOT. I also noticed the LCD display itself also gets WARM…I assume this is normal. Update (06/21/2020): I notice the Left Speaker has a 5 pin connector I notice the Right Speaker has a 4 pin connector Update (06/21/2020): Speaker Connector PINOUTs for Logic Board 820-2828