I have checked the circuit and everything seems ok. The shutter stuck closed seems to be a rare intermittent connection when certain wires are flexed, and hard to reproduce. I have verified it is normally stuck open when in LX mode, and working normally when the parallel port is disconnected.
The real problem seem to be that I can't get access to my parallel port (IBM T23 laptop/Windows XP). I have tried K3CCDTools (the free version), QCfocus, and wxAstroCapture, and for all of them, pin 2 of the parallel port stays fixed at 5V regardless of any long exposure capture attempted. So I just get a standard short exposure frame every time. I have tried a couple of independent printer control programs, tried enabling interupts on the port, but nothing so far allows me to bring pin 2 down to 0v.
I have tried manually holding the LX input to earth with shutter open, and disconnecting at just the right moment and I can get long exposure. That's at 1/5 sec frame rate - I can disconnect at the right moment occasionally using the countdown in QCfocus to judge when).
Alan