What is the year on yours? Mine says 1980.
I also found another crystal and swapped them out.
It still holds the time, but won't run. I run the
program "TIME" on the disk and the times show up
on-screen, and the cursor to the left flashes,
I assume rereading the time to show on the display
and nothing changes. If I rotate the POT clockwise
one full rev, the time increases by 6 hours exactly,
so I know it's trying to do something. If the ROM
was shot, it probably wouldn't be recognized at all,
but it knows it's a Thunderclock and see what slot
it's in. Strange.