Troubleshooting Twin Malfunctioning MFJ-989C Antenna Tuners!

MFJ-989C Antenna Tuner

SARA Thursday Night Eye Ball QSO Party
Stillwater Public Library
February 3
6:00 – 8:00 PM

Keith (AGØH) and Dave (WØOXB) both have MFJ-989C antenna tuners that have issues. These are promoted and sold as “Big Boy” tuners BUT some of us know otherwise. You may have to troubleshoot and fix them to make them work and/or get top performance!

In Keith’s case, it seems as the roller on the inductor is not making good contact (e.g., dirty roller, poor alignment, insufficient pressure, etc.). Dave’s tuner has a counter that does not repeat its readout when on the same settings.

We’re opening these puppies up and gonna get to the bottom of these – and maybe other issues.

IF you have a manual tuner and want to learn what to do – and what not to do to maintain it; come to Thursday’s Eye Ball QSO Party.

Or, just come along and watch ... hey, it’s cheap entertainment!
(You may even learn the true meaning of "MFJ"!)

Non-required Reading/Prep Work:

The MFJ-989C roller inductor tuner is a popular “Big Boy” manual antenna tuner. Specs say it will handle 3000 watts PEP input and 1500 watts PEP output – for load impedances of 35-500 ohms. This tuner is designed to match 50? output amplifiers, transmitters or transceivers to many, NOT ALL, antenna systems. Peak and average forward power, reflected power, and SWR are displayed on the unit's illuminated cross-needle meter.

This tuner uses a roller inductor "T" matching network. It continuously tunes all frequencies from
1.8 thru 30 MHz. It can match dipoles, inverted-Vs, verticals, mobile whips, beams, random wires,
and many others including SARA’s popular “OXB Special Center-fed Zepp” antenna.

The MFJ-989C has rear panel connectors for coaxial and single or two wire feedlines. The built-in “Little Boy” balun may work in some systems where balanced open wire, twinlead, or twin-axial feedlines are used. An internal six position antenna-selector switch selects a built-in 50 ohm dummy load, two coaxial line outputs, or a single wire line-balanced line output. The coaxial line outputs can be selected in tuned (with tuner's matching network in line) or direct (no matching circuit) configurations.

Disclaimer (caveat emptor): Not all connections within the MFJ-989C are always properly soldered. Some electro-mechanical components are not correctly aligned or connected! This tuner can give the avid ham troubleshooter hours of enjoyment, entertainment and frustration!

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