I did an optical clean recently on a UF75 (colour wheel, external lenses etc, I didn't dismantle the main light chamber). It had a fairly new lamp in, but was on low brightness as there was a dim/bright/dim/bright type flicker at high brightness.
After reassembly it started up and looked good brightness, but after maybe 2 minutes it started wildly flickering red/green/blue and then shut off.
Obviously, colour wheel was suspected, but it wasn't an issue previously. I hadn't touched it physically so I doubt I had damaged it. I wondered if I had cause an issue by blowing dust into it, but it started up quickly and seemed to run fine.
After lots of investigation I came across a newish YouTuber who suggested, post-cleaning, the InfraRed (IR) coming out of the lamp was flooding the colour wheel position sensor (little circuit board with sensor looking at black band on the colour wheel motor body)
Indeed, the flickering only started after the lamp reached full brightness, and I think dismantling the projector cause a full reset of the brightness settings. Also, he suggested a lamp that didn't have a good IR filter glass might be contributing. My lamp only had a green/yellow tinge (a recent lamp I now have has a red tinge).
So, all fitted with the data.
To fix the issue, I glued a tiny "shroud" around the IR sensor made out of a 1.8mm cable tie. Worked perfectly after that!
Hope that helps someone :-)