ELECRAFT K3 Modification

Elecraft K3 AF Amplifier Output Modification
Revision C, January 24, 2009
Copyright © 2009, Elecraft, Inc. All Rights Reserved

Introduction

This modification protects the K3's audio amplifier if either speaker output is connected to a short circuit or very
low impedance load. Two 470 ohm, 1/4 watt resistors are added to the output circuit to suppress potentially
damaging voltage spikes that might otherwise occur.
If desired, Elecraft will supply the two resistors for only the shipping expense. Call or visit www.elecraft.com to
order
AFOPMDKT.
The resistors are common leaded parts. No work with SMDs is required to perform this modification.

Was This Change Incorporated in My K3 at the Factory?

This modification is needed for all K3s shipped to date containing either a Revision XB or Revision A KIO3
board. You must inspect the KIO3 board to see whether the modification has been made. Modified boards will
include the leaded resistors shown in Figure 4. You can see the resistor in the lower part of the figure by removing
the top cover as shown in Figure 1 and inspecting the side of the KIO3 board facing away from the rear panel.

Tools Required

You will need a No. 1 Phillips screwdriver, diagonal cutters, long nose pliers and a temperature controlled ESD-
safe soldering iron with rosin core small diameter solder. A grounded wrist strap and ESD dissipating mat are
recommended whenever you work inside your K3.

Procedure

Observe ESD precautions when working inside your K3. Wear an ESD wrist strap or touch an
unpainted, metal ground frequently while working.
Remove the K3 top cover as shown in Figure 1 As you lift the cover off unplug the speaker wire that
.
connects to the KIO3 board in the left rear corner of the K3.
Figure 1. Removing the Top Cover.
Elecraft • www.elecraft.com • 831-662-8345