This is not really a repair or a project but if you make up the jumper plug or the DC Power lead then it is a small project and getting the power flowing again is a repair!
I was asked (anonymity respected) if I could help to get an IC-AT500 working as the unit had been purchased at a rally without any leads and plugging it into the mains didn't do anything.
These auto-tuners use a 4 pin Molex connector for DC power in with the AC/DC switch and a jumper plug controlling the current flow.
When in the DC position the AC/DC switch disconnects the power switch from the internal power supply and connects it between pin 1 and pin 2 (refer to the socket below) to enable the external power to be switched on and off with the front panel power switch and (obviously) a DC power lead plugs in to enable the tuner to be used from a battery etc. (jumper plug removed).
When in the AC position the AC/DC switch allows the front panel power switch to switch the mains current on and off, thus internal AC power supply can be used. A jumper plug needs fitting to the DC power in socket to enable the power to flow between pin 3 (DC from the internal supply) and pin 2 (power in to the tuner).
The drawing (below right) is a rough approximation of the socket. Pin 1 is at the pointed end, pin 4 is at the flat end, the colouring is my own. The connections are:
I hope this helps any IC-AT100 & IC-AT500 owners and prospective users to get the tuners powered up.
The DC fuse rating is listed as 3 Amps.
A similar system was used on the IC-251 / IC-451 / IC-551 (not 551D) and the IC-R7100 / IC-R8500 receivers. There is a difference, the DC leads and jumper plugs are NOT interchangeable so see the Icom IC-251 / IC-451 / IC-551 AC/DC Power Connection page for the details.