Elecraft K2ATOBKIT User Manual

U P G R A D I N G T H E E L E C R A F T K 2 T O R E V I S I O N B

Rev. E, April 29, 2003

In October, 2002, the K2 transceiver was updated to incorporate many modifications that had been recommended by
Elecraft or our customers. Any Revision A K2 (or Revision XC, 1999 Field Test) can be brought up to Revision B by
making the changes listed in Table 1. K2s with serial numbers 3000 and higher already include all of the changes
(except the recent PLL Upgrade, which is also discussed in this document). To determine which revision of the K2 you
have, look at the RF board, near "ELECRAFT" label at the center.

Most of the items needed are supplied with the K2ATOBKT mod kit. Other mod kits and parts must be purchased
separately as indicated in the table; these kits come with their own modification instructions. Step 9 (AF GAIN control
modification) does not require a mod kit, but you'll still need to obtain the associated application note (see page 8).

If your present K2 firmware is older than revision 2.00A, you'll need a firmware upgrade (part # FWK2MCIO)
in addition to any hardware mod kits. New firmware installation and realignment will be done in steps 11 and
12, after all desired hardware changes have been made. This ensures that calibration and test steps will only
have to be performed once.

Table 1. Modification Steps

Modification Steps (do in order)

1. Firmware Revision Check and Parameter Save RF n/a 3

2. PLL Frequency Stability at 7182 kHz RF K2ATOBKT 5

3. Misc. RF Board Changes RF K2ATOBKT 6

4. 15/17 meter and 20/30 meter Band-pass Filters RF K2ATOBKT 7

5. BFO Temperature Stability RF BFOMDKT 7

5A. PLL Upgrade (Temperature compensated reference osc.) RF E850138 7

6. VFO ALC and 10/12 meter Band-pass Filter RF E850093 8

7. Second Crystal Filter Flatness RF XFILMDKT 8

8. First Crystal Filter Grounding RF n/a 8

9. AF GAIN Control Smoothness All three n/a 8

10. Misc. Control Board Changes Control K2ATOBKT 9

11. Firmware Installation Control, RF FWK2MCIO 10

12. Alignment and Test Control, RF n/a 10

Board(s) Part # Pg.

13. Speaker Grille Cloth n/a E850089 15

NOTE: Not included are Rev. B board changes that accommodate the K60XV 60 meter adapter (RF board: VCO and
40-m low-pass filter). The K60XV manual describes these changes, which should not be made until the option is
installed. Also not included are minor changes that have no impact on operation or performance (for example, RF
board: R60 bias pot changed to a fixed 100-ohm resistor; Control board: switch S1 changed to a jumper block, P7).

1

K2ATOBKT Mod Kit Inventory

)

)

)

)

)

)

)

)

)

)

)

)

)

)

)

)

The parts supplied with K2ATOBKT mod kit are listed below. Other mod kits referenced in Table 1 include their own
parts lists.

Ref. Description Part Qty

RF-C33 Capacitor, 2 pF ("2") or 2.2 pF ("2r2"
RF-C68 Capacitor, 10 pF E530006 1
RF-C28,C29 Capacitor, 12 pF E530058 2
RF-CPLL Capacitor, 68 pF E530007 1
RF-C174 Capacitor, 82 pF E530038 1
RF-C30,C36 Capacitor, 470 pF ("471"
RF-C91 Capacitor, .001 µF ("102"
CTRL-C12 Capacitor, .0027 µF ("272"
RF-CRF, CTRL-C31 Capacitor, .047 µF ("473"
CTRL-C42 Capacitor, 0.1 µF ("104"
RF-D10 Diode, ultra low-drop Shottky, 95SQ015 E560009 1
RF-R50 Resistor, 1.5 ohms, 1/2 watt (brown-green-gold
RF-R64,CTRL-R6 Resistor, 100 ohms, 1/4 watt (brown-black-brown
RF-R1, R2 Resistor, 220 ohms, 1/4 watt (red-red-brown
CTRL-R12 Resistor, 820 ohms, 1/4 watt (gray-red-brown
CTRL-R7 Resistor, 1.78 k, 1/4 watt, 1% (brown-violet-gray-brown
RF-RREFA, RREFB Resistor, 10 k, 1/4 watt (brown-black-orange
RF-R11 Resistor, 47 k, 1/4 watt (yellow-violet-orange
RF-R18 Resistor, 1 M, 1/4 watt (brown-black-green
RF-RFC11 Toroid, 20 turns #26 enamel on FT37-43 core E680003 1
RF-RFC15 RF choke, miniature, 100 µH (brown-black-brown
CTRL-L1 Inductor, shielded, 82 mH ("823", dark gray, cylindrical
Misc. Enamel wire, #26, red (for RFC11) E760002 3 ft.

E530047 1

E530004 2
E530001 1
E530055 1
E530025 2
E530011 1

E500025 1
E500010 2
E500002 2
E500001 1
E500026 1
E500015 2
E500067 1
E500024 1

E690013 1
E690015 1

i

Caution: Some parts in the K2 can be damaged by static discharge. While making modifications, use an

anti-static wrist strap. Alternatively, you can touch a grounded, unpainted metal surface (do this often).

i

Updating the K2 to revision B involves a considerable amount of component removal. You will need a
full-size, hand-operated vacuum desoldering tool. The Edsyn model AS196 Anti-Static Solder Sucker ($25), is
an excellent choice. Before removing a component, straighten its leads on the solder side (use a small tool while
heating the solder joint). Next, clean out the holes using the desoldering tool. Finally, pull the component out,
being very careful not to damage pads, plated-through holes, or traces on the top or bottom sides of the board.

2

1. Firmware Check and Parameter Save

Determine what revision of firmware you have by

turning the K2 on while pressing and holding any
switch. You'll see a display such as: 2 . 0 3 d 1 . 0 7 .
The number on the left is the firmware revision of the
main microcontroller, U6 on the Control board. The
other number is the firmware revision for the I/O
controller (IOC), U1 on the RF board. Record both of
the numbers here: K2 _______ IOC _______.

i

If your K2 firmware revision is older than

2 . 0 0 A , you'll need to install new firmware after
making all desired hardware changes. You may need to
install a new IOC in addition to the main micro­controller. This will be explained later.

Supplemental Menu Parameters: The D I S P L A Y
switch is used to access additional parameters when
editing certain menu entries. These include sidetone

source (S T L entry), 8R Hold mode (T - R entry),
Auto-Detect mode (I N P entry), and Fan mode (P A

entry, secondary menu). These will be set up
appropriately during new firmware installation (page

10) and do not need to be recorded here.

CAL Settings (Table 3): To access CAL settings, use
the primary menu to scroll to C A L , hold

E D I T to edit

the parameter, select a CAL function with the VFO
knob, then hold

E D I T again to activate the function.

After recording the setting, tap M E N U to exit, then
tap M E N U

again and access the next CAL function in

the same manner.

Whether or not you plan to install new firmware,
you should record your present configuration settings
in Tables 2 - 5. The BFO frequencies (Table 5) will be
needed if you make the Temperature Stability changes.

Table 2. Menu Parameters

Primary Menu Secondary Menu

(Rev. 2.00 up1)

Entry Param. Entry Param.

ST L SLCH
ST P RATES

T-R DOT

RPT FPLY

INP PORT

IAB SPLT

SSBA Po28

2

SSBC

SSBC SSBCr

RTTY

LCD RTC

GRPH RIT

OPT ACC

ATU AT2/D19

3

RANT PA

CAL Table 3 TRN1

PF1 TRN2

Table 4

PF2 TRN3

1

To switch between the P R I and S E C menus, tap

D I S P L A Y after tapping M E N U .

2

If RTTY is set to O N (Rev 2.00 up), and r mode has

been selected with
changes to

3

If you have revision 2.03 or later firmware, the name of
this menu entry is
never used).

S S B C r . Record both settings if applicable.

M O D E , the S S B C menu entry

D 1 9 . Otherwise it is A T 2 (which was

3

Table 3. C A L Settings

CAL Function Parameter

OFF n/a

FCTR n/a

CUR

TPA n/a (stored by KPA100)

S LO

S HI
PLL n/a (CAL PLL will be done later)

FIL Table 5

Transverter Band Displays (Table 4): You'll only
need to record these settings if you use the transverter
bands. To access transverter band display settings, tap

M E N U

, then tap D I S P L A Y to switch to the
secondary menu, then scroll to the desired T R N x
menu entry. Hold E D I T to access it. Tap D I S P L A Y
to cycle through the five parameters for each
transverter band display. To select the next transverter
band setup, first tap M E N U

to return to scroll mode.

Table 4. T R N x Band Displays (Rev 2.00 up)

Xvtr # On

RF IF OFS OUT

/Off

TRN1
TRN2
TRN3

(see next page for Table 5)

4

Filter and BFO Settings (C A L F I L , Table 5)

: Before recording filter/BFO data, switch to any of the lower bands

(160-17 m) so LSB/USB settings won't be swapped in CAL FIL. Connect the internal frequency counter cable to TP2
(BFO). To access filter and BFO settings, tap M E N U

, scroll to C A L , hold E D I T to access the parameter, and
change it to F I L . Hold E D I T again to activate the C A L F I L function. Record filter bandwidth settings (e.g. 0 . 7 0 )
for each mode and each filter. Cycle through the modes by tapping M O D E
filters are selected using X F I L

. (RTTY mode, r , and RTTY reverse are only available with revision 2.00 and up

and holding C W R E V when appropriate;

firmware. The associated secondary menu entry, R T T Y , must be set to O N .) After all filter bandwidths are recorded,
tap B A N D -

followed by D I S P L A Y to show the BFO frequency. Record the BFO frequencies (e.g., 4 9 1 3 . 1 0 ) for

each mode and filter, as you did for the filter bandwidths.

Table 5. Present Filter and BFO Settings (C A L F I L )

Mode

CW

CW Rev.

LSB

USB

RTTY

RTTY Rev.

F L 1 B F 1 t F L 2 B F 2 F L 3 B F 3 F L 4 B F 4

4

If you're not familiar with filter and BFO configuration, review the instructions for CAL FIL in the K2 Owner's manual, starting

on page 85.

4

2. PLL Frequency Stability at 7182 kHz

Whenever the VFO is tuned to the 5 kHz band segment
centered at about 7182 kHz, the PLL reference
oscillator and VCO will be at exactly the same
frequency. At this point, on a small percentage of K2s,
coupling between the two oscillators can result in a
"wavering" quality on both transmit and receive. If

your K2 exhibits this symptom, it must be corrected. It
compromises signal quality, and may prevent VFO
linearization (CAL PLL) from working correctly.

Frequency Stability Test

Pin 13

You'll first need to identify the segment of 40
meters over which the two oscillators are at the same
frequency. Switch to 40 meters, LSB or CW mode, and
tune to about 7182 kHz. Then activate C A L F C T R
using the menu. Alternately insert the internal counter
probe into TP1 (VCO) and TP3 (PLL reference
oscillator), and make sure they indicate the same
frequency (in the 12 MHz range). They'll be equal over
some 5 kHz segment, typically 7179-7184, but
possibly lower or higher

5

. (Note that you can tune the

VFO while in C A L F C T R .) Don't change modes or

filters, as this will move the target range.

Range: 7____- 7____ kHz (mode: ___, filter: ___ )

Listen to a few signals in this range to see if they
exhibit the "wavering" sound. Compare them to signals
outside the range. You can use another ham transmitter
as a signal generator. (Don't change modes or filters.)

Modifications to Cure Instability

The following modifications can be used to cure
the instability, if required. Try them in order, and stop
when the symptom disappears. All necessary parts are
included in mod kit K2ATOBKT.

MC145170

(bottom view)

Pin 16

MC145170

(bottom view)

C90

Figure 1

X

C90

Figure 2

RFC15

 Make sure C70 and C71 (VCO area) have the shortest

possible leads.

 Solder a 68-pF capacitor (RF-C

RF board, between pins 13 and 12 of the MC145170,
U4 (see Figure 1). Keep the lead length short.

 Add an RF choke in series with U4 pin 16. First locate

point "X" in Figure 2. Cut the indicated small trace
segment between pin 16 of U4 and capacitor C89 (on
the top side). Next, solder a miniature 100-µH RF choke
(RFC15) across the cut as shown in Figure 3. Finally,
solder a.001-µF capacitor (C91) from pin 16 to ground.

 Remove C70 (4.7 pF).

5

Due to differences in the way old and new firmware did

CAL PLL.

PLL) on the bottom of the

5

C91

C90

Figure 3