Definitive answer to flickering screen?

Just like a good soup the ingredients matter!

I can’ tell you what your exact issue is but the time I was working with a ton of them we found the following:

The first issue is how clean the power and ground is. Basically, we ended up getting one building each station their own fill-in UPS. So both the voltage was stable and the sine was clean as well.

We also made sure the outlets where properly grounded and the breaker panel was likewise properly grounded. We had to get the two buildings re-wired as the ground was poor on a quite a few outlets.

It also turned out the transformer servicing one of the buildings was bad as well. We had the power company place a few power meters in the building to monitor the powers quality (this should be a free service if you request it). Make sure you get a copy of the logs and save it when you finally get all the kinks worked out as a base reference for later.

We did need to replace a few of the displays cable assemblies as they where worn or just damaged! How you store the cable is important! You want to be a seaman! Loose coils, no kinks or excessive bends. One of the engineers made a vey tight coil strapped up and a second did a bow-tie each killed the cable! The tension of the internal wires broke the connections internally.

We did note some of the backlight drivers on the logic board had issues. I can’t tell you what exactly the tech replaced but I do suspect it was the capacitors as over time they do loose the efficiency. or the driver chip was replaced. Of the twenty of so displays I think half ended up getting rebuilt logic boards over a two years before they jumped to HP systems - hiss!!

I would recommend doing a search for the schematics for the logic board 820-2997 as well as the 2011 27” iMac 820-2828 and its board-view as its basically the same backlight circuit to compare between them.