Icom IC-7410 – PTT tuner start doesn’t work

I have an IC-7410 with R1 of the firmware installed.

I have attempted to use its PTT tuner start feature (triggers ATU tune on PTT if frequency changed a significant amount)  with an MFJ-993B ATU, but it fails.

The symptoms are that the IC-7410 does not transmit its tune carrier, it remains in the mode active when PTT was pressed.

Tuner operations initiated from the IC-7410 TUNE switch appear to all work as expected.

Above is a logic trace of the ATU control wires on PTT tune. everything looks good, when the /START signal is recognised as valid, the ATU asserts KEY and the IC-7410 should put tune carrier out… but it doesn’t and the ATU aborts after about 0.5s without tuning.

This works fine using an IC-7000, so it appears that after making transceivers that properly implemented this function, and presumably having test suites that ensure it is working, the new IC-7410 fails.

This is not the fault of the MFJ-993B, but a failure of the Icom IC-7410 firmware. This defect might be shared with other Icom transceivers.

It was this deficiency that created the need for Reflected power alarm for the MFJ-993B.