MFJ MFJ-941EK, Versa-Tuner II Instruction Manual

Model MFJ-941EK

CAUTION: Read All Instructions Before Operating Equipment

MFJ ENTERPRISES, INC.

Tel: [phone] Fax: [phone]

VERSION 1A

INSTRUCTION MANUAL

300 Industrial Park Road

Starkville, MS 39759 USA

COPYRIGHT 2013 MFJ ENTERPRISES, INC.

C

DISCLAIMER

Information in this manual is designed for user purposes only and is not

intended to supersede information contained in customer regulations, technical
manuals/documents, positional handbooks, or other official publications. The

copy of this manual provided to the customer will not be updated to reflect

current data.

Customers using this manual should report errors or omissions,
recommendations for improvements, or other comments to MFJ Enterprises, 300
Industrial Park Road, Starkville, MS 39759. Phone: [phone]; FAX: (662)
323-6551. Business hours: M-F 8-4:30 CST.

MFJ-941EK Tuner Kit Instruction Manual

INTRODUCTION

General Information:

This manual contains all the information you'll need to build, calibrate, and use
your new MFJ-941EK Versa-Tuner II kit. The Versa-Tuner II is actually four very
useful station accessories combined into one package. The first is MFJ's wide­range 300-Watt T-network that can match virtually any HF antenna you're likely to
encounter. The second is our highly accurate dual-range SWR/Wattmeter that
features cross-needle metering. The third is an eight-position RF-routing switch
for selecting a variety of antennas, either through the tuner or around the tuner in
bypass mode. And, finally, there's a built-in 300-Watt 4:1 balun to accommodate
antennas using balanced feedline. Despite its versatility, the circuitry and
mechanical layout for the MFJ-941EK are straight forward, and these instructions
will guide you through assembly from start to finish.

Before You Start:

Prepare a clean work surface and use muffin tins, egg cartons, or small paper
cups to organize your parts. To reduce eyestrain, choose an area with strong
overhead lighting and add a high-intensity desk lamp for close-up work.
Construction requires the tools listed below:

[ ] Soldering iron with a narrow chisel tip.
[ ] Soldering-iron holder with a moistened cleaning sponge.
[ ] Your choice of leaded or lead-free solder with rosin or no-clean flux.
[ ] Small needle-nose pliers or surgical hemostat.
[ ] Side-cutter type wire nippers.
[ ] Solder sucker or de-soldering braid
[ ] Magnifying glass or loupe for reading component markings
[ ] Phillips-head screwdriver
[ ] 5/64" Allen wrench (for knobs)
[ ] 3/32" Allen wrench (for shaft coupler)
[ ] 1/4" nut driver (for 4-40 hardware)
[ ] 5/16" nut driver (for 6-32 hardware)
[ ] 3/8" nut driver (for 10-32 hardware)
[ ] 7/16" nut driver (for insulated terminal posts)
[ ] 1/2" nut driver (for 3/8" ID control-nuts)

As you work, watch for the four most common kit-building errors:

1. Wrong Part: Identify, sort, and organize all parts ahead of time.

2. Reversed Polarity: Double check diode and meter polarity.

3. Defective Soldering: Routinely check for cold solder joints or bridged tracks.

4. Omitted part: Check off each construction step as you go.

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MFJ-941EK Tuner Kit Instruction Manual

INTRODUCTION

Before soldering, always inspect leads and terminals for oxidation. If dull, clean
or burnish them with a small brass-wire hobby brush or glass-fiber brush
(available at Radio Shack). Clean surfaces and good heat distribution are the
keys to strong solder.

MFJ-941EK Parts Inventory:

Use the bill of material (BOM) on the next page to account for all the pieces in
your kit, checking each part off as you go. If there's a missing or damaged item,
write down the MFJ part number and contact MFJ for replacement (see Warranty
page for instructions). Most parts are packed in three plastic bags -- one for small
hardware items, one for pc-board components and pre-cut wire, and a third for
larger parts.

Figure 1.1: MFJ-941EK Tuner Kit

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MFJ-941EK Tuner Kit Instruction Manual

INVENTORY

Begin your inventory with the hardware bag. For identification purposes, PH =

Phillips Head, SM = Sheet Metal Screw, SS = stainless steel, KEP = nut with an
integral lock washer, OD = Outside Diameter, and ID = Inside Diameter.

[X] Qty Description MFJ Part Number

[ ] 8 4-40 x 3/8" Machine Screw, PH 654-0375
[ ] 3 4-40 x 1/2" Machine Screw, PH SS 654-0500
[ ] 3 4-40 x 1/4" Threaded Aluminum Spacer 716B-0250
[ ] 11 4-40 Hex Nut, KEP 705-0440K
[ ] 2 6-32 x 1/4" Machine Screw, PH 656-0250
[ ] 1 6-32 x 1" Machine Screw, SS, PH 656-1000
[ ] 1 6-32 Hex Nut, KEP 705-0632K
[ ] 2 6-32 Hex Nut 705-0632
[ ] 1 6-32 Flat Washer 710-0643S
[ ] 2 6-32 x 1-1/4" OD Fiberglass Washer 714-06125
[ ] 1 6-32 x 1/4" Nylon Spacer 718-1218-0250
[ ] 8 #6 x 3/8" Screw, Sheet Metal, Black 656S-0375B-A
[ ] 2 #6 x 3/8" Sheet Metal Screw 656S-0375A
[ ] 2 10-32 x 3/32" Set Screw, Hex 660-0187-SA
[ ] 1 10-32 x 3/4" Machine Screw, PH 660-0750
[ ] 1 10-32 Hex Nut, KEP 705-1032K
[ ] 1 10-32 Wing Nut 705-1032S-W
[ ] 1 #10 Solder Lug 720E-0621L
[ ] 1 #10 Split Lock Washer 711-1037S-SL
[ ] 2 #10 Flat Washer 710-1050
[ ] 1 1/4" ID Heyco Shaft Bushing 740-2102
[ ] 1 1/4" ID x 1/2" OD x 3/4" Coupler, 10-32 725-3105
[ ] 1 1/4" x 3-1/2" Metal Shaft, 1/2" Flatted End 725-2112
[ ] 3 3/8" Hex Control Nut, Panel Mount 705-3732RI
[ ] 3 3/8" ID x 5/8" OD Flat Washer, Metal 710-3762
[ ] 1 3/8" ID x 5/8" OD Shoulder Washer, Fiber 714S-3762
[ ] 2 3/8" ID x 5/8" OD Flat Washer, Fiber 714-3762
[ ] 4 3/8" ID x 3/4" OD Flat Washer, Fiber 714-3775
[ ] 1 3/8" ID x 5/8" OD Flat Washer, Teflon 714-3762T
[ ] 4 3/8" ID x 3/4" OD Flat Washer, Teflon 714-3775T

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MFJ-941EK Tuner Kit Instruction Manual

INVENTORY

Next, inventory the circuit board bag containing small pc-board components

and pre-cut wire. Color codes and number codes are included to help you sort
resistors, capacitors, and chokes.

[X] Qty Description MFJ Part Number

[ ] 2 100Ω 1/4W Resistor (brown, black, brown) 100-2100
[ ] 1 150Ω 1/2W Resistor (brown, green, brown) 101-2150
[ ] 1 3.3k 1/4W Resistor (orange, orange, red) 100-3330
[ ] 1 47K 1/4W Resistor (yellow, violet, orange) 100-4470
[ ] 4 50-K Trimpot, 10-mm Horizontal Mtg 133-4500B
[ ] 1 33pF Disc Ceramic Capacitor, 1kV (33) 200-0033-2
[ ] 1 220pF Disc Ceramic Capacitor, 1kV (221) 200-0220-2
[ ] 5 .01uF Disc Ceramic Capacitor, 50-V (103) 200-2100
[ ] 1 3-10 pF Trim-Cap, Horizontal Mtg 280-2010
[ ] 1 680 uH Choke (blue, gray, brown) 401-5680
[ ] 1 Directional-Coupler Xfmr, .37-OD Toroid 10-01003
[ ] 2 Schottky Diode, CDSH270 (or 1N270) 302-0270
[ ] 1 Switch, DPDT, Push-On/Push-Off 504-0022
[ ] 1 Switch, 4PDT, Push-On/Push-Off 504-0023
[ ] 1 2.1-mm PCB Power Jack 601-6021
[ ] 3 Hookup Wire, 5", Black 871-2400-0500
[ ] 1 Hookup Wire, 5", Red 871-2422-0500
[ ] 1 Hookup Wire, 5" Violet 871-2477-0500
[ ] 1 Hookup Wire, 5" White 871-2499-0500
[ ] 1 Tie Wrap, 4" Nylon 745-2149
[ ] 8 Buss Wire, 5-1/4", #16 Tinned 870-0016-0525
[ ] 1 Buss Wire, 6-1/2", #16 Tinned 870-0016-0650
[ ] 1 #4 Shoulder Bushing, Teflon 740-1012T
[ ] 1 Brass Eyelet (Small) 725-4108

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MFJ-941EK Tuner Kit Instruction Manual

INVENTORY

This list covers the large item bag of larger items:

[X] Qty Description MFJ Part Number

[ ] 1 PC Board, Single-Sided 861-0949E
[ ] 3 Insulated Binding Post, Red, with Hardware 606-0003
[ ] 4 SO-239 UHF Chassis Mount Connectors 610-2005
[ ] 1 300-W 4:1 Balun on 1" Toroid Form 10-10002B
[ ] 1 2-1/2" Precision Cross-Needle SWR Meter 400-3083A
[ ] 1 Molded Plastic Meter-Mount Bracket 736-0201
[ ] 2 12 - 313 pF Air-Variable Capacitor 282-2006
[ ] 1 3/8" OD Plastic Pushbutton, Red 760-2140
[ ] 1 3/8" OD Plastic Pushbutton, Black 760-2122
[ ] 4 1/4" ID x 1" OD Knob, Black 760-0035
[ ] 1 Switch, 8PDT, 2-Section Rotary 500-0028-1
[ ] 1 2.1-mm DC Power Cable with Coax Plug 620-8321

Finally, these separate bag items are bagged seperately.

[X] Qty Description MFJ Part Number

[ ] 1 941E Inductor and Switch Assembly 10-13003
[ ] 1 MFJ-941E Aluminum Chassis 800-0941E
[ ] 1 MFJ-941E Front Panel Decal (pre-installed) 782-0941E

[ ] 4 Rubber Feet (pre-installed) 770-1162

[ ] 1 MFJ-941E Chassis Cover, Black 804-0941E
[ ] 1 Assembly and Operating Manual 925-0941EK

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MFJ-941EK Tuner Kit Instruction Manual

CONSTRUCTION

Key Assembly Instructions:

Key words are used to shorten the length of the assembly steps to one line. Find
means to pull specific items from the parts inventory for installation. Identify
means to look for a mark or feature that orients the part for installation. Install

means to clean leads, insert them at a specified location, and bend or wrap them

so the part stays in place. Solder means to apply solder, inspect the connection,
and nip off protruding leads or pins. Legend refers to silk-screen lettering on the

printed circuit board.

Circuit Board Assembly:

Find the circuit board and take a minute to survey the component-side legend for
various part locations. When you're ready to begin construction, find the five
resistors listed below:

(2) 100 ohm (brown, black, brown)
(1) 150 ohm (brown, green, brown)
(1) 3.3K (orange, orange, red)
(1) 47K (yellow, violet, orange)

[ ] Install a 150 ohm 1/2-Watt resistor at R1 and solder.
[ ] Install a 3.3K resistor at R2 and solder.
[ ] Install a 100 ohm resistor at R3 and solder.
[ ] Install a 100 ohm resistor at R4 and solder.
[ ] Install a 47K resistor at R9 and solder.

Next, find four (4) 50K trimpots (black, 3/8" OD, 3 pins)

[ ] Install 50K at R5 and solder.
[ ] Install 50K at R6 and solder.
[ ] Install 50K at R7 and solder.
[ ] Install 50K at R8 and solder.

Find the four (4) disc ceramic capacitors listed below. Note that three leftover .01
uF capacitors will be installed later.

(1) 33pF (33)
(1) 220pF (221)
(2) .01 uF (103)

[ ] Install 33 pF at C3 and solder.

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MFJ-941EK Tuner Kit Instruction Manual

CONSTRUCTION

[ ] Install 220 pF at C5 and solder.
[ ] Install .01 uF at C6 and solder.
[ ] Install .01 uF at C7 and solder.

Find the 3-10 pF trimmer capacitor (white ceramic, ~1/2" OD, 3 pins).

[ ] Install at C4 and solder.

On the pc board, locate the legend marking for C12 (next to trimpot R5).

[ ] Form a 1/4" jumper using a clipped-off lead end. Install at C12 and solder.

Find the 680-uH RF choke (blue, gray, brown).

[ ] Install 680-uH at L2 and solder.

Find two (2) Schottky diodes, CDSH 270 (blue) and identify the banded end.
Refer to Diagram 1.

Cathode End

Diagram 1: Diode Orientation

[ ] Install a diode at D1 with the banded end (cathode) toward the D1 legend.
[ ] Install the second diode at D2 with banded end toward the D2 legend.

Find the following items:

(1) Switch, DPDT, push-on/push-off (6 pins)
(1) Switch, 4PDT, push-on/push-off (12 pins)
(1) 2.1-mm PCB power jack

[ ] Install the DPDT switch at SW1. Confirm all pins are fully seated, and solder.
[ ] Install the 4PDT switch at SW2. Seat pins, and solder.
[ ] Install the 2.1-mm power jack at J1 and solder.

Find the 8PDT pc-mount 2-section rotary switch (from the larger parts bag)

[ ] Orient the switch over the pc-board legend at SW4 and install.

[ ] Confirm all pins are firmly seated and solder.

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MFJ-941EK Tuner Kit Instruction Manual

CONSTRUCTION

Find the six (6) pre-stripped 5" lengths of jacketed hookup wire:

(3) Black
(1) Red
(1) White
(1) Violet

[ ] Locate three holes marked Ground on the edge of the pc board near R8.

[ ] Install a black wire in each and solder (free ends to be connected later).

[ ] Install a red wire at LMP (behind SW1) and solder.
[ ] Install a violet wire at FMTR (between SW1 and SW2) and solder.
[ ] Install a white wire at RMTR (opposite side of SW2) and solder.

Find the following items to construct SWR transformer T2.

(1) .37" OD toroid with bifilar winding
(1) #4 Teflon shoulder bushing
(1) Small brass eyelet
(1) 5-1/4" length of #16 buss wire

Refer to Diagram 2 below:

Side View

Top View

2

Install

Buss Wire

In Eyelet

1

Install Eyelet and

Solder to Pad

3

Diagram 2: SWR Transformer Installation

Brass eyelet

Bend Wire Over

and Solder to Eyelet

4

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Install
Shoulder
Bushing

Install Toroid

Over Eyelet

5

T2

Install Wires and Solder

6

BussWire

Shoulder Bushing

MFJ-941EK Tuner Kit Instruction Manual

CONSTRUCTION

[ ] Locate the pc legend for T2.

[ ] On the solder side, install the brass eyelet through the T2 pad, as shown.
[ ] Solder the eyelet flange in place, but do not fill the opening with solder.
[ ] Insert buss wire into the opening and make a 90-degree bend at the end.
[ ] Solder the bent end of the wire to the eyelet.
[ ] On the component side, install the toroid over the protruding eyelet.
[ ] Install the Teflon shoulder bushing on top, pressing it into the toroid center.
[ ] Confirm toroid is flush with pc board and wires aligned with mounting holes.
[ ] Install and solder all three leads (twisted tap lead goes in the center).

Find six (6) additional 5-1/4" lengths of #16 buss wire.

[ ] Install a buss wire at D/L and solder (rear of SW4)
[ ] Install a buss wire at WIRE and solder
[ ] Install a buss wire at COAX2 and solder.
[ ] Install a buss wire at COAX1 and solder.
[ ] Install a buss wire at C2 and solder (right front of SW4).

The sixth buss wire is connected between the pc board and a tab on SW4. Refer
to Diagram 3 below:

Wire

D/L

SW4

Connect

and Solder

Diagram 3: SW4 Tab Location

[ ] Install a buss wire at the unmarked hole between D/L and WIRE, and solder.

[ ] Locate the exposed solder tab on top of SW4's front wafer.

[ ] Route the buss wire to the designated terminal, install, and solder.

This completes circuit board sub-assembly. Note that several tuner models use
the same pc board and some parts locations are not used for this project. Before
moving on, take a few minutes to inspect and double-check your work.

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