Just inherited a Model 4 with twin floppies.
The CRT seems to powerup but no text on screen..
The lower drive light comes on but no other activity.
That, IIRC, is correct behaviour if you don't have a boot disk.
Try turning it on (or pressing 'Reset' -- the orange button in the top
right cornder of the keyboard) while holding down the 'BREAK' key. You
should geht a CASS? prompt. Hit 'ENTER' (Tandy's name for Return), then
you'll get a MEMORY SIZE? Prompt. 'ENTER' again, and you'll be in ROM
BASIC. This can save/load to cassette, but not disk.
You should be able to find a TRS-DOS 6.x (or LSODS 6.x) boot disk image
on the web somwehre.
Is there a common failure mode for these critters?
There are seceral (most common being the infernal cables between the CPU
board and disk controller and RS232 interace on early machines). But
let's make sure it's failed first :-)
-tony