Mods & Repairs

MFJ 949E Versa Tuner Inductor Switch Replacement

MFJ 949E Inductor Switch LocationA common problem with the MFJ 949 antenna tuners is the burning of the inductance rotary switch. The problem usually occurs when the switch is operated while transmitting – DON’T do it!

Fortunately, replacement of the switch used in the MFJ 949 is quite straightforward, all you require is a new single pole, 12 way rotary switch, very easy to find from a good electronics supplier or eBay.

Before you rush in and remove the old burnt switch, you need to note where the the wires are attached in reference to the inductance coil and also which one is connected to the switch common terminal. An easy method of doing this is to simply use a permanent marker pen, putting a single mark on the wire that corresponds to position “A”, 2 marks to “B” etc – I’ll leave it to you to figure out your own way.

When you’re sure you know where the wires are attached on the switch, go ahead and de-solder them. Next remove the knob from the front panel, it’s normally held on by a grubscrew although a friction fit knob may be fitted. Undo the retaining nut and withdraw the old switch out from inside the tuner.

burnt switch waferWith the old switch removed you will see just how bad the contacts are burnt, if the switch is disassembled it may be possible the rear side contacts are also burnt, as in this case.

Take the new rotary switch note which contact is connected to the common terminal, then fix it into the tuner using the nut – don’t tighten the nut or replace the knob just yet. Rotate the switch until you can solder the feed to the common terminal so it’s very close to the correct orientation. At this point you can finger tighten the nut to keep the switch in place while you reattach the wires to the inductor coil in their correct positions.

When you’re satisfied everything is correct, fully tighten the nut, determine which position inductance is selected by observing which contact is currently connected to the common. You will have to visually check which inductance position is selected as you can’t test with a multimeter. Replace the knob so it corresponds with the selected inductance and finally replace the lid.

Share this page: