Since we're talking about printer problems, here's mine. This is
on a '486, with lpt, using psroff (not the system command, the
package) to print on a LaserJet, with August and later sources.

There are two separate problems. One of them is dropped
characters. It happens about once a page or so. Yes, the cable is
attached firmly, it's short enough, and it's shielded.

The other problem is that every once in a while my system comes
to a complete, dead, halt. Nothing works short of the Big Red
Switch.

If I boot my system with no printer cable attached but the card
with the parallel port in, I don't get any hangs. If I attach the
printer cable, leave the printer off, and reboot, I'll sooner or
later get a hang. That latter, even if I turn the printer on for
some amount of time.  Those are the knowns.

Two more things I think are true but I don't have solid proof: if
I attach the printer cable, leave the printer off, reboot and
leave it attached for awhile, and then remove it, I'll get a hang
sooner or later. If I boot with the printer cable detached and
then, to use the printer, I turn it on, attach the cable, use it,
detach the cable, and then turn the printer off, I won't get a
hang.

If I had to guess, it would be that I have two problems. One is a
defective cable, causing the dropped characters and transients
when the printer is off. The other is with the driver,
misbehaving if interrupts or other changes on the printer lines
happen when it isn't expecting them.

At the moment, I don't have the time to track this down and I do
have a workaround, but I thought I'd report the problem.