A buzzing sound from the top-left was driving me crazy. It appears to be the power supply.
I printen out the repair manual and carefully read it before starting. Although the suction cups are not required, they make it very easy to remove the front panel. Removing the small connectors with the spudger was not so easy. In the end I simply used my fingers.
Once the LCD is out, it is easy to replace the power supply. Putting all the connectors back in the LCD is much easier than removing them.
I did wear some glove at my left hand. This allowed my to firmly hold the LCD, without getting finger prints on the screen.
Total repair time was 1 hour.
The best advise I can give is: Prepare well. I made sure all my tools were in arms reach and had some small bowls to put the screws in. A little flashlight is also practical.
Heavy-Duty Suction Cups (Pair)
Probe and Pick Set
iMac Intel 27" EMC No. 2309, 2374, 2390 or 2429 Power Supply