From the looks of it, I was pretty sure that the blob was going to be something wrong with, or wrong on the surface of, one of the lenses, mirrors, or filters. Yes, it looked a little like an LCD ruined by being left in a freezing car overnight, but not quite. So I dug in to follow the light path through the projector and see if it would be apparent what was wrong.
After popping the cover and removing the main circuit board, I could see most of the periscope-like light enclosure. I removed a couple of lenses that dropped in from above, which were clean, and looked at a couple of mirrors, which were also clean. The next thing I wanted to check was the LCDs.
In order to get to them, I had to take off the collar above/around them, remove the two cooling fan / speaker assemblies, and remove the main lens. The LCDs were mounted to the lens carrier and looked fine; their removal left access to this cavity where the RGB light paths converge.
I didn’t notice it until later, but someone had already been here before. Loctite on the RG screw tabs and missing from the B tab.
From a different angle, the problem was obvious.
The filter between the blue light path and the blue LCD is all melty. Bad.
First things first. I gently peeled off the Bad, scrubbed all the goo off the glass carrier with Goo Gone, washed all the Goo Gone off with Dawn, rinsed the Dawn off with water, and dried the water off with a paper towel. (Life is sooooo complicated.)
Here it is all shiny and ready for . . . whatever comes next.
While I was in there, I detached and examined the other two filters. They didn’t look colored, just a light neutral grey in a very familiar sort of way. Apparently the filter isn’t what makes the blue blue (that’s the blue half-mirror further upstream), so maybe I can just put it back together and see what happens.