NAD M33 issues, don't know where to start

Not sure if yours does, but some NAD can be upgraded with USB stick and correct power on sequence.  Like press a button while powering on.  Thats how my m51 updated.   Good luck

OK just picked mine up after a month at the repair shop.
Tech notes are- no characters in the display but backlights present. Need LCD unit in order to correct.

The LCD Display was $332.10 and 4 hrs labor $360

total of $730.17 after  $38.07 WI (USA) sales tax

I talked to the guy who did the repair and he said it was not an easy swap, glue, 2 sided tape, etc.

Also noticed another M33 sitting on the rack, I asked about it and all he said it was different issues and they haven't gotten to it yet.

Anyway I fell I'm still ahead for buying at $4200 used, they are now $5999 new

Don't have a NAD myself, but one item you might check is to remove the case cover and see if all the connections look right.  Computer display screens are typically plugged into the mother or video board using a flat ribbon cable.  Yours may have worked loose.  And check the connection at the display end of the cable, too.  Finally, note the ribbon cable may not have an actual "plug" on the ends, but rather just a stiffer section of cable with silver or gold connectors. They slide into a female connector on the circuit board that has a up/down slider that moves maybe n 1/8th of an inch to lock it down, so are a little trickier to use than a normal plug.

Ouch.  That's a pretty new unit to be incurring that type of repair charge.  I did consider this model.