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MFJ Antenna Tuner - needed maintenance

Discussion in 'Radio Circuits, Repair & Performance' started by KB5UBI, Apr 3, 2012.

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  1. KB5UBI

    KB5UBI Ham Member QRZ Page

    I recently hooked up my 20 year old MFJ 941 and found it was not up to par. I opened it up and found several of the pop rivets were preventing a good ground on the SO239s.

    I drilled out all of the rivets and replaced them with screws, star lock washers and nuts. I soldered an additional bus to all of the SO2392.

    Upon further inspection, I found a cold solder joint where the bottom of the inductor connects to chassis ground, a bent inductor wire almost touching one of the tap wires, and an intermittent variable capacitor. I corrected the bad connections and cleaned the cap with contact cleaner.

    While I had it open, I removed the crappy 4:1 voltage balun and replaced it with a home brewed 1:1 current balun, so I no longer need to use my external balun for ladder line.

    20 years ago, the tuner worked great, but they do deteriorate after sitting for 8 or 10 years. Now it's like new again.
  2. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    It must have been 'radio moths'. Lord knows nothing would leave the MFJ factory in that condition! :)
  3. KO6WB

    KO6WB Premium Subscriber QRZ Page

    After setting for so long it's amazing it did anything. It's great you were able to bring it back to life. Electronic devices are meant to be used on a regular basis. Leaving something to just sit and hoping it will improve with age is for wine and some whiskey, not amateur radio gear.
  4. K7MEM

    K7MEM Ham Member QRZ Page

    I bought a MFJ-16010ST Antenna Tuner at a swap meet. The "ST" stands for "Super Tuner". But it turns out it was an odd production piece and was not offered by MFJ for very long. Initially it was very hard to dig up a manual, but I managed to find one.

    Anyway, when I tried to use it, it didn't respond the way I expected. I couldn't match anything. When I initially opened it up, everything looked fine. But I finally took it completely apart and found a unsoldered wire that connected the toroid coil to one of the tuning capacitors. I soldered it on it's post, put it back together, and ran some tests. It worked like it should. I figure that's the reason it was for sale in the first place. I still use it now and then.
  5. KB5UBI

    KB5UBI Ham Member QRZ Page

    Besides the MFJ tuner, I hooked up my FT-920 which had been stored in the closet for ten years and the transmitter will only put out 5 to 10 watts. KO6WB is correct about not using the equipment. I do prefer 12 year old bourbon.
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