Harbach Electronics SK-401 User Manual

SK-401 “SOFT KEY” INSTALLATION INSTRUCTIONS

PARTS S UPPLIED WIT H THIS KIT:

(1) SK-401 “Soft Key” Circuit Board Asse m bly
(2) 6-32 x ¼” Round Head Screws
(1) Nylon Threaded Spacer
(1) #6 Internal Tooth Lock Washer

To start the installation, read these instructions very carefully. Now unplug the amplifier
and remove any input, output and control cables that may be connected to the back of the
amplifier. Place the am plifier ups ide do wn with the re ar pan el facin g you an d rem ove 6 sc rews an d
the bottom cover. You are now ready to proceed with the installation.

( ) The exact mounting location of the SK-401 is not too critical. Be sure to keep the RED and

BLACK leads as short as possible. The most convenient place I have found is just behind

(or next to, depend ing on your v ers ion o f the L-4B RF d ec k) the 24 volt s upp ly terminal s trip

on the right side n ear the ON-OFF rocker switch. Try to align the unit such that the BLUE

wire is nearest the wiring harness and the flat part of the large HEXFET transistor is facing

the front of the RF d eck.

( ) Once you have decided on a location, mark a location where the large hole in the SK-401

is. This is where the mounting spacer attaches to the SK-401 and also the location of the

hole for the mounting screw. Very carefully drill a hole that will clear a 6-32 screw at the

point you just marked (#27 drill). Do not use to o m uch pre ss ure b ecaus e you w ant the drill

to stop after just penetrating the chassis. Clean up any burrs from the hole.

( ) Place the #6 lock washer o nto one of th e 6-3 2 x ¼” sc rews a nd p la ce the screw through the

hole you just drilled. Screw the threaded nylon spacer from the SK-401 kit onto the screw

and tighten we ll without stripp ing the threa ds in the sp acer.

( ) Mount the SK-401 circuit board onto the nylon spacer using the other 6-32 x ¼” screw.

Position the board as previously described.

( ) Unsolder the WHITE & BLUE wire from the ant enna rela y jack on th e back p anel.

( ) Remove the diode that is between the antenna relay jack and a small 1-lug terminal strip

next to th e jack. Yo u c an discard the diode. The lug should not have anything connected

to it after you removed the diode

( ) Route the BLUE and YELLOW wires from the SK-401 along (or in) the wiring harness so

that both wires end up n ear the ant enna relay jack.

( ) Solder the YELLOW wire and the WHITE & BLUE wire (unsoldered from the antenna jack

earlier) to the terminal of the 1-lug terminal strip next to the antenna jack. This effectively

connects the se wires togethe r.

( ) Solder the BLUE wire from the SK -401 to th e an ten na relay jack . Th is w ire will be attached

where the WHITE & BLUE wire was unso ldered from earlier.

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( ) Solder the RED wire from the SK -401 to the +24V DC lug of the terminal strip near where

you mounted the SK-401. This lug has the positive (+) end of an electrolytic capacitor, the

cathode (banded) end of a diode and a 2.2K resistor soldered to it.

( ) Solder the BLACK wire from the SK-401 to a convenient chassis ground. The terminal

strip described above USUALLY has 1 or 2 ground lugs available for this. O ne or more

lugs are directly connected to ground as they are used for mounting the large terminal strip.

( ) Replace the bottom cover and any cabling.

This completes the installation of the SK-401 “Soft Key” module. You may not SEE any
difference in the operation of your exciter or amplifier, but you will know that you have reduce d the
stres s on the exciter’s ke ying relay or transistor.

SK-401 “SOFT KEY” M ODULE

PARTS LIST

R1 & R2 22KΩ ¼ W 5%
R3 10KΩ ¼W 5%
C1 & C2 0.1µF 50 VDC CE RAMIC
D1 1N4005 (1A 600 PIV)
D2 1N60 GERMANIUM
Q1 MPS2222
Q2 IRF610 HEXFET (N-CHANNEL)

HARBACH ELECTRONICS

Jeff Weinberg – W8CQ

468 County Road 620

Polk, OH 44866-9711

[phone]

htt p://www.harbachelect ronics.com

info@harbachelect roni cs. com

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