Still working my way through this entire thread, but was hoping I might solicit some advice on how to proceed with what is now my 3rd HT3550...
First Unit - Unfortunately at this point I hadn't found this thread and didn't note the HW revision on this unit (though the focus dial did have a pin on it which make me believe it was at least a somewhat newer unit) . Overall it looked very good to me, except for some rather extreme focus issues. Upper left and lower right corners were very fuzzy compared to the rest of the image, and appeared to be out of focus in 'opposite' directions. ie dialing in one corner made the opposite corner worse. Colors looked good to me, especially in HDR, though being my first projector there may be issues I'm not aware of / looking for that I've missed. Focus was bad enough that I contacted support, who was very helpful and immediately issued an RMA
Second Unit - Clearly a refurb, including a sticker labeling it as such. HW revision 1-101. Upon mounting this unit, I could tell immediately the focus issues were gone. Great clarity across the entire image. Unfortunately, as I started to run some test content through it, I saw issues getting stuck with a split image. Typically could cycle picture modes or stop/start HDR content to clear the issue, but annoying none the less. Also nothing concrete, but felt like the colors didn't pop in quite the same way. I'd discovered this thread by then however so maybe it was all in my head. Updating FW seemed to reduce the frequency of the split screen issue, but did not eliminate it. Unit was also significantly louder than the first, both the fan as well as the internals especially when shifting in/out of 4k/HDR. Another RMA was issued.
Third Unit - This one arrived this morning, HW 2-103. Box wasn't obviously reused, and no refurb sticker on this unit, no obvious signs it's a refurb, so that's promising. Got it mounted and the first thing I noticed is that I really had to move the vertical shift to the extreme to get everything aligned on the screen despite using the same mount with everything in the same position. It's ceiling mounted and I was just barely able to get the image low enough to fit on the screen. Not sure if this means anything but figured it's worth pointing out. After getting alignment dialed back in, it became apparent that there are again some slight focus issues in the upper left / lower right corners. Much less severe than the original unit, but certainly worse than the first replacement. Colors seemed more in line with the original unit to me. Not much time with it yet but so far noise levels seem more in line with the first unit as well.
So where I'm stuck now is how to proceed. While still showing some focus issues, its probably something I could live with. That said, after seeing just how clear and sharp the second unit was, it's hard to not notice it. I could roll the dice again and see what happens with another RMA, but I feel like I'm as likely to get another problematic and potentially worse unit than I am to see an improvement. It's also becoming something of a hassle constantly unmounting / remounting units on a weekly basis. Is the fact that both newer revisions I've received showed similar focus issues as compared to the older revision simply a coincidence or something inherent to the newer revisions? Should I see if support is willing to let me hold off a few months while they hopefully sort out these issues and try another RMA then? Any thoughts from folks who have been more closely involved with this projector for a while would be appreciated.