So on my Yaesu FT-710, I set it up with the MFJ-939 with the appropriate Yaesu interface cable. Set the radio to use the external instead of the internal tuner. I was hoping it would be as simple as hitting the tune button on the front of the radio as I would with my IC-7200 and LDG IT-100 tuner. No such luck. The tuner will power on with the radio but hitting the tune button on the FT-710 does nothing. Well, it just gives me three rapid beeps. If I press and hold the tune button it will give me two quick beeps after one second.
Now then, if I put the rig into CW mode and key the mike it'll send a tone that the tuner will pickup and tune to. Well, most of the time. Sometimes I've got to turn the tuner off then back on, then key the mike before it will start automatically tuning.
Don't know if anybody else running the FT-710 has seen this behavior with an external tuner. Maybe it's different and works as it should with the LDG? For some reason I'd thing LDG would have gotten it right and it's just an MFJ thing.
On the plus side, the 939 is a very quick tuner when it comes to tuning a frequency it already has in memory. Just a click and it's done. Now if it doesn't have a frequency or needs to do a full re-tune, it takes considerably longer than my LDG did on the 7200. But the MFJ also has a much broader tuning range. Can even get a match for my 40M OCFD to 80M even. I know, I know, it still is inefficient, but it kinda sorta works. The LDG looked at it and just said: Nope!