Hmm, well mine has just died I think...
I bought a new monitor and tried plugging it in via the adapter and while it continues to work fine in anything up to ST High or TT medium, the TT high mode is not working any more.
The display is mono, but the resolution doesn't change from TT medium, and the monitor display is massively distorted.
I plugged the previous working in TT high monitor back in and same issue...
I think one of the connectors on the adapter is slightly loose now. It was always a tight fit on the cable so you had to push quite hard when plugging it in, but I wasn't careful about it (forgot!) when plugging the 2nd monitor in.
I suspect something is disconnected inside...
1977 VCS Heavy Sixxer (Boxed)
1990 Atari 1040STE, 4MB, UltraSatan, TOS 2.06, TT Touch -> Atari SC1435 Colour CRT Monitor
1991 Atari TT030, 2/64MB, Int 8GB Gigafile SCSI2CF, TOS 3.06, CaTTamaran Accelerator -> Atari TTM195 19" Mono CRT Monitor
1993 Atari Falcon030, 14MB, Int 4GB IDE2SD, TOS 4.04 -> Atari PTC1426 Color CRT Monitor
Amiga, Mac, DOS, Newton, SGI, Sun, NeXTStation and more!