iMac stuck loading at 75% with full fans constantly. A1312 2009

[hcs-mac]

I have a 2009 A1312 iMac I am trying to get fixed but I can't really figure out what the problem with the OS loading.
I have tried multiple HDD's however all seem to get stuck at the apple logo with 75% loaded.
I think the reason the fans are 100% are that there is no OS found and the LCD temperature connector is broken.
Could the broken connector on the motherboard be causing the OS not to boot fully on a HDD which is not the original one for the system?
I have been able install the OS on the HDD's on the system however I cannot boot into the OS.

 

[RyanXM]

Very unlikely that the temp sensor is keeping the OS from booting. In order for macOS to load, you really only need a minimum config: CPU, RAM, Video Card, Screen, speaker (just for those computers with a POST chime), Keyboard & Mouse.

Have you tried Safe Mode? Hold Shift as soon as you hear the POST chime.
Have you tried an SMC and PRAM reset?

 

[zone23]

I thought if you replaced the HDD in older iMacs it would cause the HDD fans run full speed because the HDD is missing the temperature senor that the Apple HDD has built into it. I've used this for a very long time (see link below). That of course doesn't answer the question as to why it wont boot, maybe bad RAM? I would try just a single stick at first.

http://www.hddfancontrol.com/

 

[RyanXM]

I thought if you replaced the HDD in older iMacs it would cause the HDD fans run full speed because the HDD is missing the temperature senor that the Apple HDD has built into it. I've used this for a very long time (see link below). That of course doesn't answer the question as to why it wont boot, maybe bad RAM? I would try just a single stick at first.

http://www.hddfancontrol.com/

The 2009 and before models used an external temp sensor for the HDD. As of the 2010 and after, Apple puts custom firmware on the 3rd party HDD (Hitachi/HGST, WDC, Seagate) and uses the jumper pins to transmit HDD temp from SMART.

 

[hcs-mac]

The 2009 and before models used an external temp sensor for the HDD. As of the 2010 and after, Apple puts custom firmware on the 3rd party HDD (Hitachi/HGST, WDC, Seagate) and uses the jumper pins to transmit HDD temp from SMART.

I have tried safe mode, I have tried SMC and PRAM resets and still the same thing.

I do not hear a boot up chine however I am not 100% the speakers are even working.

I have currently got a 500GB Seagate driver plugged in with the temperature sensor plugged into the HDD as well.
I have managed to get the LCD temp connector plugged in and the fans are no longer at full constantly however I still cannot boot into the OS.

The bluetooth and LCD ribbon cable on the top left both seem to be in bad shape, Could this be causing problems?

 

[RyanXM]

Have you tried unplugging everything but the essentials? Essentials being: HDD, LCD (Backlight Board, LVDS, and Temp Sensor), one speaker.

Unplug the following: bluetooth module, camera, ODD, IR sensor, mic.

Make sure all fans and sensors are plugged in to ensure proper cooling.

 

[hcs-mac]

Have you tried unplugging everything but the essentials? Essentials being: HDD, LCD (Backlight Board, LVDS, and Temp Sensor), one speaker.

Unplug the following: bluetooth module, camera, ODD, IR sensor, mic.

Make sure all fans and sensors are plugged in to ensure proper cooling.

After trying everything I could I had to give up, I believe the motherboard is faulty unfortunately.