When you use the Tune function... with a AH-4 or equivalent external tuner, the rig kicks down to 10-15 watts for the tuning procedure.? Then reverts back to whatever mode you were in prior to hitting the tune button. . and either stops when it sees about 1:1 SWR or it times out after a certain amount of time.
There are many companies that sell a dongle ($30)? that you install on the 4 pin molex on the rear and that simulates an AH4 so you can tune even with a manual tuner.. This will work with many ICOM rigs. I also use it on my IC756proII..
The capacitor is not specified voltage, but 15-25 VDC will work..
Larry W8LM
Larry Macionski