Well if a repairman said the board was bad it must be bad :-) Sadly but
that would not always be true. I would put the odds at 1% it's the
board & 99% it's not the board from the problem you described.
To me it sounds like a shorted wire or stuck button. Did he disconnect
the button wire & the receiver at the motor head? If not disconnect
both & jump across terminals 1 & 2 on the motor head & see if the
operator works properly. If it does it's obviously not the board.
Assuming it works w/ both disconnected, re-connect the button wire &
test unit again. If operator runs on it's own or doesn't work at all,
either the wall button is stuck or their is a short in the wire.
If operator works w/ wall button connected, re-connect the receiver to
see if the problem comes back. If the problem comes back, remove the
batteries in all transmitters & try the wall button. Re-connect
batteries one at a time & if the operator takes off as soon as the
battery is connected that transmitter's button is sticking or broken
(inspect the metal tab on the circuit board under the plastic button to
make sure it isn't flattened or cracked.
Obviously you could inspect the transmitters and/or connect the
receiver before the wall button, but I would think if it was a stuck
transmitter button the battery would be dead by now & the opener would
already be working fine (until you put in a new battery).
I hope you tell me that the repairman already did all of this but my
money says it's not the board even if he did troubleshoot it this far.