4 Status LEDS, Chime, No Display, Hot PSU?

I've recently been given an iMac EMC2428 with issues that I'm attempting to repair.

Going off of the status lights, I get the standard 501 (First LED, far right) trickle power light, which is good. However when I attempt to start it, I get similar responses;

Start WITHOUT LCD; LEDS 502 and 503 light up, followed by a chime plus sounds from the CD drive, and HDD spins up. But after a few moments, Fans spin up to full and stay there. It can be there for a few hours with little, but noticeable heat.

Start WITH LCD (Plugged in but propped so I can see the lights); Chime, cd sounds, and HDD spin, same fan issue as above. But after a few minutes, I can feel a quite significant heat from the left hand side, from the PSU, CPU heatsync, etc. as well as a smell of heat. However, nothing on display. No light, no faint display, zilch.

I have not left it for very long with it running with the LCD as it does it worryingly hot, and I don't currently have a temp sensor handy to check which components are hot.

At first, I thought this was a power draw issue from the LCD backlight, but even with the backlight disconnected, the heat issue occurs.

Questions:

- Is there a pinout for the 14 pin PSU connector? I'd like to test output voltages.

- Is this a common issue, and am I headed the right way, by looking at the PSU?

- Is there any way I can use an external display, or test if the GPU is even attempting to output a signal?

- Is there a way I can test the LCD monitor? So I can rule that out.