MFJ-939 Autotuner First Impressions

I received the MFJ-939 yesterday without incident. The unit came with the MFJ-5114Y interface cable to use with my Yaesu FT-450D radio. The radio also comes with a banana plus to connect a longwire antenna and a DC power cord. First up, I wired the power cord with Anderson Powerpoles. After disconnecting the LDG tuner and reconnecting the radio PC interface directly to the radio (rather than passing through the LDG tuner) I went ahead and connected the new tuner. This was pretty straightforward. Coax connections from the radio and to the antenna and ground wire were connected pretty easily. The interface cable uses an 8 pin din connector to connect to the rig and the other end is an RJ-45 connector. I went ahead an ran through the reset and self tests on the tuner and no problems were indicated. On the Yaesu, this tuner is supposed to emulate the Yaesu FC-30/FC-40 autotuners when using the interface cable. The rig is configured to use external ATU. All in all the wring and configuration were very easy. Unfortunately, I could not get the tuner to work with the FT-450D in this configuration. So much for plug and play…sigh.

I spent the next couple of hours debugging the problem and searching the internet for any clues. Basically what was happening is that when I press the tune button the rig nothing would happen with the tuner. The tuner light would blink and then the antenna light would start blinking. I disconnected the cable and manually tried to tune by first applying a 5W  CW signal then hitting the tune key on the tuner. This time things started happening and a match was found. So at least now I know the tuner operates properly just not in FC-30 configuration. After playing around with the connections several times I finally just left the interface cable off. I programmed the FT-450D Voice/C.S. key to activate SWR mode which sends out a 10W CW carrier. When I press and hold this key the tuner automatically starts up and finds a match. This is really quick.

I called MFJ Technical support this afternoon and it was refreshing to have a person answer the phone after two rings. I described the problem to him and told him my suspicion was a bad cable. He felt the problem was more likely with the firmware on the tuner and suggested the Voice/C.S. workaround. No resolution to the interface cable problem but he was going to try and get me the cable pinout.

I went ahead and started playing with the tuner and even with the terrible band conditions today confirmed that everything still works. I made contacts to Colorado, Brazil, Guatemala, Canada and Bonaire. I like that the tuner finds a match so quickly and it really facilitates changing bands quickly with my DXtreme Antenna.

I tested the cable pinout a bit and found some things that just don’t look right so I will likely call MFJ again tomorrow and share my findings. I am still thinking that the cable has a problem. Specifically that lines 7 and 8 on the RJ-45 are reversed. I will measure again tomorrow then call up MFJ and see if I can get a confirmation on what the pinout should be.

Overall the tuner is a keeper just a bit more hassle getting it working than I expected.

UPDATE: Just to be clear the tuner itself performs as it should. Last night I carefully checked the cable pinout against the FT-450D and MFJ tuner manuals. From what I can see it looks like pin 7 and pin 8 on the RJ-45 side of the cable are switched. I have sent my observations to MFJ and opened a trouble ticket. I do not have the tools to attempt a rewire of the connector so I will see if MFJ will make good on the cable.

UPDATE (11/18/15): MFJ confirmed that the cable is not wired right, specifically that pin 7 and pin 8 are swapped. They have promised to send an updated cable today.

UPDATE (11/30/15): New cable arrived and I verified the cable was wired correctly. There is communications now between the rig and tuner now but I still have an issue. Pressing tune on the radio starts the tuning cycle, the tuner finds a match BUT it never returns control to the radio. I’ll call MFJ again tomorrow and see if this is what the firmware change fixes.

UPDATE (12/1/15): MFJ is sending a new chip containing updated firmware. They are not sure that this will fix the issue but its worth a try. If this doesn’t work I will need to send the unit in for a swap or just live with the problem. Fingers crossed!

UPDATE (12/8/2015): Received and replaced the MCU chip with the new firmware. The swap was pretty straight forward and it helps that I had an IC puller. After opening the cover you need to remove the front panel and then the circuit board attached to the panel. After swapping out and reassembling the tuner I hooked up the cable and set the rig to external tuner. Same behavior as before, i.e. the tune cycle starts but control is not returned to the rig. So this is my final update on this. I don’t plan on returning the unit to MFJ as the SWR button workaround still works and I don’t want the downtime this close to the holidays.


8 responses to “MFJ-939 Autotuner First Impressions

  1. Gregg December 8, 2015 at 12:57 pm

    I found your blog & wanted to let you know you’re not alone with respect to this issue: I have the same radio & tuner and am in the same boat! Your post did allow me to get the tuner working but, as you’ve observed, it still does not integrate with the FT-450D. MFJ is sending me a new chip as well so I look forward to seeing if that resolves the problem. I look forward to reading your updates on this adventure!



    • rjbono December 8, 2015 at 4:44 pm

      Just posted an update…short answer the chip did not fix this problem. Let me know how it works out for you…


      • Gregg December 12, 2015 at 2:27 am

        Got the “new” chip today … No change. It’s a nice tuner but the interface for the 450D doesn’t work as the manual describes. MFJ is supposed to consult with their engineer and follow up with me next week.


  2. rjbono December 13, 2015 at 12:02 am

    Let me know what happens Greg. Interested to see what they come up with.


    • David Hood December 28, 2015 at 4:53 pm

      My FT-991 will not work with the MFJ-939Y… it just sits there with no reponse from the radios tune button. Odd thing is that my MFJ-929Y works just fine (?!?). I am wondering if there are CAT command changes from Yaesu involved here??
      73, WA9IVB


      • rjbono December 31, 2015 at 6:36 pm

        I had the same problem initially with the tuner and traced it to a bad 5114Y cable. Basically they had switched the last two wires on the RJ-45 end of the connector (i.e., pins 7 and 8 were swapped). Once I got the corrected cable, the tuner would respond by starting a tune cycle but never returns control to the rig. This is where I left off and have been using the C.S./SWR key workaround ever since.


      • David Hood December 31, 2015 at 9:50 pm

        Thanks… This is interesting. I am on the Yahoo Group >>Yaesu FT-991, and a fellow there claims his 939 works great right out of the box with the Yaesu FT-991. I am now wondering if MFJ has changed the firmware?!. I have had the MFJ939 for over six months now. Its strange that my 5114Y cable works fine with my FT-991 and the MFJ-929. But I will check the cable just in case.
        Many Thanks and 73, Dave WA9IVB


  3. Rob August 4, 2016 at 11:52 pm

    I wish I had read your blog before I bought the 939. I have a Yaesu ft-450d with the exact problem. I can tune in cw on any power level. The 939 does not give control back to the yeasu with out me going off frequency. Help support a MFJ seems baffled.


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