This is what an Auto Response Board looks like inside. The PCB is attached to the back panel. When that is taken off access to the reed switches and LEDs is clear. This particular ARB had a faulty reed switch (For more information on reed switches please goto the Conchess repair page)

The LEDs and reed switches are set into the wooden board. Despite the fuzzy picture you can probably make out the holes in the corner of each square which accommodate the LEDs and the holes at the centre of each square where the reed switches are. They are then soldered to the tracks which criss cross the board. So apart from one thing it would be relatively easy to change a reed switch. The one thing is that the reed switches are bent a hairpin shape to get into the hole. And the other thing.........  The other thing is that there is a diode soldered to the reed switch in series. See photo of a broken reed switch below.

So when I replaced the reed switch, not knowing where to get these diodes and exactly what they do, the only option was to take it off the broken switch and solder it back onto the replacement. Bending the switch wires into the hairpin shape requires care. Soldering the diode to it I found extremely fiddly. Anyway I managed it in the end and the ARB now works 100%.