but last night I changed the hdmi -dvi connectors and the nuts that go in to the 990 came off with the connectors on all 3 connections.
Either the nuts were loose or the HDMI-DVI connector screws were over-tightened. The good news is that they are both threaded the same way so if the screw stops turning you can be pretty certain that both the standoff nut and the connector were fully seated (assuming neither were cross threaded).
We see a lot of loose stand-offs at work. We either Loctite them back in, being careful not to slop Loctite, or we use a small wrench to hold the stand-off nut when removing the screw.
Finger tight plus a quarter turn is typically typically tight enough for the stand-offs.
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975/7075/SMS-1
Aperion Verus Grand Towers & Bookshelves, Verus Forte Center, Infinity Surrounds, Ultra-X12
Oppo BDP-203, XBOX360, Xbox One
LG 65" OLED
RR2150 w/Klipsch SCR-2