MFJ 941E ATU - Replacing That Pesky SWR Light

Its many years ago now since I bought the MFJ-941E matching unit.  MFJ have a very American style of advertising, and reading one of their leaflets sometimes brings to mind a rather dodgy second-hand car salesman's pitch!  The endless use of excited italics to highlight rather unexciting features is also rather quaint.

But that would be to do MFJ a disservice.  The 941E has matched just about anything I have ever thrown at it.  This afternoon, its SWR panel light gave up, giving me a chance to open it up to fix.

These are the very tidy workings inside my MFJ 941E:

Fair play, that's an honest day's work by MFJ for about £140.

 
You can't really find anything to criticise in there, especially mindful of the price.  The 4:1 balun is absolutely tiny, but I always use my homebrewed transformers just outside the shack with balanced line anyway, and never now use the twin input into the MFJ.

Now, back to the SWR panel meter light.  For some utterly unknown reason, MFJ, at least for a time, produced this transmatch using a small incandescent bulb to light it up.  Inevitably, after a couple of years, it blows.  I decided to replace it with some old white LEDs from a broken 6V torch I had just thrown in the bin.  I hastily recovered it, took out the two LEDs, took an educated guess at the correct voltage and current, and added a couple of 90 Ohm resistors in series to bring the nominal 13.8V DC output from the station PSU down to something that didn't turn the LEDs into little heaters!

Two LEDs from an old 6V torch, plus 180 Ohms added resistance give me a nice new SWR meter light for pennies.

I just glued the little circuit board holding the two LEDs to the outside of the panel meter, at the top, keeping the LEDs clear of any plastic and in free air, just in case of any excess heat production.

It works a treat, and I doubt I will ever again have to change the light source for that SWR meter!

Cool blue LED replaces mellow yellow incandescent glow.