button 0 is stuck on IIgs

[shack@deimos.frii.com (Randy Shackelford)]

I located something I thought I'd never find up in Denver today, a signature
edition IIgs with ROM 0 and the original VGC. I bought it and brought it home
but when I tried running the diagnostics, it turns out that button 0 is stuck
in the pressed state. There's no joystick attached, and it's not the keyboard
either since it does the same thing with the original and a standard keyboard
II I tried on it. Any ideas? I could always swap the board with one of my 
spares but I'd prefer not to take out the original plus it'd mean swapping
ROM and VGC chips.
-- 
Randy Shackelford                                 
shack@frii.com