Have assembled the circuit on a breadboard but can't get LSDJ sync going.

The MIDI in/PIC/button stuff all seems fine, with the various midi
messages making the LEDs flash in the manner the manual suggests they
should, leading me to believe the problem is somewhere around the 7414
hooked up to the link cable.

However I've checked + double checked all the connections with a
multimeter (including from the 7414 pins on the breadboard to the end
of the link cable) and it all seems fine. The only slightly odd thing
is that with power on the two non-ground pins going to the link cable
seem to be joined together, but they're not when the power's off, so I
guess that's just a quirk of whatever the circuit does when in action
(which, in case you haven't guessed, I really don't understand)

Anyway, was wondering if anybody has any ideas or suggestions as to
what might be wrong. I'm using a gameboy color at the mo as that's all
i had a handy link cable for, but will probably buy another and try
with my classic in a bit, just in case the link port itself is dead.