Building K2 #7750


ELECRAFT K2 #7750 with options

The K2 #7750 Assembly Manual Purchased 8 Sep 2017
The KIO2 Assembly Manual Purchased 18 Jan 2018
I will be using prewound toroids from the Toroid Guy where possible.

Now that I have the kit and all the options that I want in it. It is time to get started.


Kit Inventory started 12 Feb 2018
Inventory completed. Let's start building.

There are six steps in the K2 assembly process
Control Board assembly
Front Panel Board assembly
RF Board assembly and test part I (control circuits)
RF Board assembly and test part II (receiver and synthesizer)
RF Board assembly and test part III (transmitter)
Final assembly

First the Control board

Sort the parts in groups.


(L) parts, (R) Control Board.

HINT:

When installing components try it keep the alignment the same.
On resistors the first significent color band facing the left side or top of the PCB.
Component with writing should all face in same direction if it is possible.
It will ease trouble shooting should the need to do so arises.

Install resistors R5 (33K ohms), R2 (3.3M ohms), R3 (10K ohms), R4 (5.6K ohms)
R6 (100 ohms), R7 (1.78K ohms 1%), R8 (100 ohms 1%), R9 (806K ohms !%), R10 (196K ohms 1%)

Install resistors R16 (10 ohms), R17 (3.3M ohms), R21 (270K ohms), R20 (2.7 ohms)

Install resistor packs
RP6 (5.1K ohms), RP1 (3.9K ohms), RP7 (33K ohms)
RP2 (82K ohms), RP3 (47K ohms) RP5 (470 ohms), RP4 (82K ohms

Install potentiometer R1 (50K ohms)

Install L1 (82mH) shilelded inductor
Install diodes D1 (1N4148) and D2 (1N4148))

Install 'RESISTOR' R22 (82K ohms) at D3.

Install capacitors C2 (.001uf), C3 (.01uf), C4 (.047uf), C7 (331pf),
C6 (.047uf), C8, (39pf), C9(.01uf), C10 (.01uf), C12(.0027uf)

Install capacitors C5 (.01uf), C14 (.047uf), C17 (.01uf)
C42 (0.1uf), C16 (.047), C11 (.01uf), C19 (.047), C21 (33pf)

C23 (.01uf), C20 (0.001uf), C18 (.01uf)
C43 (.001uf) C27 (.022uf), C25 (0.1uf)
C26 (0.1uf), C24 (.0027uf) C31 (.01uf)

C34 (.001uf) C30 (.047uf), C40 (.01uf)
C35 (.01uf) C36 (.0027uf), C39 (.01uf)
C41 (.01uf), C37 (.01uf), C38 (680pf)

Install electrolytic capacitors C1(2.2uf), C13 (22uf)
C15(100uf), C28 (220uf), C29 (100uf), C33 (2.2uf) and C32 (22uf)

Observe polarization

Install ceramic trimmer capacitor.

Align slot parallel with crystal outline.

Install transistor Q12 (PN2222A), Q11 (PN2222A), Q1 (2N3906
Q2 (2N3906), Q3 (2N7000), Q4 (2N7000), Q5 (2N7000)

Q6 (J310), Q7 (J310), Q8 (PN2222A), Q9 (MPS5179), Q10 (MPS5179P

Install Crystals X1 (5.068MHZ), X2 (4.000MHZ)

Be sure to ground the crystal cases

Install voltage regulators U4 (LM2930T-8) U5 (78M05)

use 4-40 screws, lock washers and nuts to secure regulators.

Install 40 pin IC socket at U6

install Dual row 10 pin at P4 next to P5
install 3 pin connector at P7 with shorting block

Install 2 pin connectors at P5 and P6

Install jumpers at R18 and R19

On bottom of PCB install resistors R12 (820 ohms) and R11 (47k ohms)

Install 6 pin connector at P1

Install 20 pin connector at P3

Install 36 pin connector at P2

Following ESD PROCEDURES install the following IC's
U2 (LM833), U1 (NE612), U3 (LM6482), U7 (25LC320)
U8 (MAX534), U9 (LM380), U10 (LM660), Microcontroller U6 (1647AJY)

USE A CONDUCTIVE WRIST STRAP

Key Shaping Components (Required)
on the bottom of PCB

Actual construction of Control Board Assembly completed
Resistance checks are now needed

Finished control Board assembly


~ ~ ~

Now the Front Panel Board

Install the 16 pushbutton switches

Install resistors R12 (120ohms), R10 (33 ohms), R9 (220 ohms)
R11 (470 ohms), R6 (4.7K ohms), R7 (4.7K ohms), R14 (100K ohms)

On the bottom, R16 (15K ohms), R15 (10K ohms)

Install resistor packs RP2 (120 ohms) and RP1 (100Kohms)

Install 1N5817 diodes at D4, D5 and D6

OBSERVE ORIENTATION

Install capacitors C1 (.047uf), C2 (.01uf) and C3 (.047uf)

Install capacitor C9 (.01uf)

On the bottom.

Install transistors Q1 and Q2 (PN2222A)

Leads must be 1/8" (3mm) or less.

Install ground jumper on left and right ends of PCB.

Install 40pin IC socket on BOTTOM of PCB

Following ESD PROCEDURES install the following IC's
U4 (TPIC6B595), U3 (TPIC6B595) and U2 (74HC165)
and install LED BARGRAPH

USE A CONDUCTIVE WRIST STRAP

Install microphone jack (J2) in lower left hand corner.

Install two 3/16" (4.8mm) standoffs.

Install a 3/16" (4.8mm) standoff on top of PCB.
next to square hole by C2

Install two 1/"(6.4mm) hex standoffs 1/2" (12.7mm)
on the BOTTOM of PCB

Install audio-taper panel mount potentiometers at R3 (5K ohm)
Install linear-taper (5Kohm) potentiometers at R1, R2, R4 and R5

DO NOT PUSH ON THE SHAFT ONLY THE CASE

Install 20 pin single row female connector
at J1 on the bottom of PCB. It must mount FLAT

Install GRAY key caps at S1 an S3

Install square key cap at S7

Install remaining key caps.

Following ESD PROCEDURES install IC U1 (PCF8566)
on the BOTTOM of the PCB. Observe orientation

USE A CONDUCTIVE WRIST STRAP

Install Diffuser using spacer to level diffuser 1/8" and parallel to PCB
Install LCD on the Diffuser. USE CAUTION LCD IS GLASS

Install bumper pads on bottom top corners

Status view before Final Front Panel assembly

NOTE: BEFORE PEFORMING RESISTANCE CHECKS CENTER POTENTIOMETERS


RESISTANCE CHECKS

Final Front Panel assembly
Install Green bargraph filter

Install Faceplate bezel

Install the 4 VFO wires

Mate the Front Panel Assembly to Front Panel Faceplate

Assemble VFO subassembly

FRONT PANEL ASSEMBLY COMPLETED

REAR VIEW AND FRONT VIEW


NOW!
TO THE RF BOARD

Install 5 2-D fasteners on bottom of PCB.

Install 2 3/16" (4.8mm) standoffs on bottom of PCB.

Install 28 pin IC socket on top of PCB

Install 17 latching relays ON TOP of PCB


# # 26 FEB # #


Install resistors R1 and R2 (220 ohms)

Back Left corner of PCB

Install capacitors C1 and C2 (.001uf)

On the left edge of PCB

Install electrolytic capacitors C105 and C106 (2.2uf)

Near front left corner of PCB

Install resistors R35 and R36 (82 ohms)

Just right of C105

Install resistor R115(.05 ohms 3 watts)

Front right corner of PCB

Install capacitor C111 (2.2uf) and resistor R113 (82 ohm)

Just left of R115

Install 2 pin speaker connector P5

Observe orientation

Install hi-current diodes D10 (95SQ015) and D12 (SB530)

Right edge of PCB

Install capacitors C77 (.001uf) and C196 (.047uf)
and resistors R69 (100k ohms ) and R66 (2.7k ohms)

Near diode D10

Install self-resetting fuse F1

Near diode D10

Install J1 the Key jack

Back left corner of PCB

Install J2 Headphone jack

Near front left corner of PCB

Install S1 Power switch

At the right front corner of PCB

Install DC input J3

At back right corner of PCB

Install Antenna jack J4 (BNC)

Just to left of J3

Install voltage regulator U2 (78L06) capacitor C139 (0.1uf)
capacitor C140 (.001uf) and resistor R64 (100 ohms)

Near U1 in middle of PCB

Install Z5 ceramic resonator

Near U1

Install resistor R65 (10K ohms)

On bottom of PCB near U1

Install diodes D8 and D18 (1N4148)

On bottom of PCB, Observe orientation

Install 6 pin female connector J6

NOTE! MUST BE FLUSH AGAINST PCB

Install 20 pin female connector J8

NOTE! MUST BE FLUSH AGAINST PCB

Install 36 pin female connector J7

NOTE! MUST BE FLUSH AGAINST PCB

Position 20 pin right-angle connector P1 on BOTTOM OF PCB

NOTE! MUST BE FLUSH AND PARALLEL AGAINST PCB

Install 2 grounding jumpers near U1 on top of PCB

Install 2 grounding jumpers on bottom of PCB

One near U1 and 1 near back edge of PCB

Following ESD PROCEDURES install IC U1 (PIC16F872)
THE I/O CONTROLLER. Observe orientation

USE A CONDUCTIVE WRIST STRAP



# # 28 FEB # #


ASSEMBLE THE ENCLOSURE

Prep and install the side panels

Install the bail on bottom and then install the bottom of enclosure

Install front panel with front panel assembly

Two views of the front panel assembly

Install control panel assembly on front panel assembly

Two views showing assembled control and front panel assembled

K2 #7750 is begining to look like a transceiver

The next step is Test and Alignment Part One.


# # 01 MAR # #

Test and Alignment Part One.

Power applied should see " INFO 201"

Should see "ELECrAFt" on display

Should see "7100.00c" on display

Tap display button and should see voltage and current

Testing the Band Switches
You can hear relays clicking
A VIDEO CLIP ON CHANGES

Optical Encoder test....PASSED

Relay Test..... PASSED

Keyer Test.....PASSED

Frequency Counter Probe and Test....PASSED

Audio Amplifier and Tone Generator Test....PASSED

S-Meter Alignment..... COMPLETED

Set The AGC Threshold.....PASSSED

Bargraph Current Test.....PASSED

Alignment and Test Part One Completed


ASSEMBLY PART TWO


# # 02 MAR # #

Install resistors
R9 (100K ohms), R16 (100K ohms), R10 (470 ohms)
R31 (10K ohms), R32 (10K ohms), R33 (15K ohms)
R30 (120 ohms), R28 (27K ohms), R20 (270 ohms)
R21 (100K ohms), R22 (3.3M ohms)

R25 (2.7K ohms), R24 (2.7K ohms), R15 (33 ohms)
R14 (10K ohms), R13 (10K ohms), R12 (560 ohms)
R17 (100K ohms), R11 (560 ohms) R5 (2.7Kohms)
R78 (22 ohms), R6 (100 ohms), R7 (68 ohms), R8 (100 ohms)

R92 (33 ohms), R91 (820 ohms), R93 (820 ohms)
R72 (470 ohms), R95 (2.7K ohms), R96 (2.7K ohms)
R96 (2.7K ohms), R74 (47 ohms), R73 (2.7K ohms), R97 (33 ohms)

R80 (680 ohms), R81 (1.8K ohms), R79 (1.8K ohms)
R82 (18 ohms), R101 (10K ohms), R107 (100K ohms)
R111 (5.6K ohms), R112 (22 ohms), R90 470 ohms)
R89 (100 ohms), R88 (470 ohms), R84 (18 ohms)
R85 (150 ohms), R83 (4.7 ohms)

Install resistor packs RP2 (10K ohms), RP6 (100K ohms), RP4 (100K ohms), RP5 (100K ohms)

Locate, Assemble PLL upgrade kit. Install at RP3 location

OBSERVE and CONFIRM ORIENTATION "BEFORE SOLDERING"


# # 03 MAR # #

Install glass diodes D11 and D13 (1N4148)
Black diodes D7 and D6 (1N4007)

Install varactor diodes MV209 (look like two legged TO-92 transistors)
D16, D23, D24, D25, D26 and D39

Install 1SV149 varactor diodes (look like 3 legged TO-92 transistor with center leg cut off)
D17, D21, D22, D29, D30, D31, D32, D33 and D34

Install TO-92 transistors Q17 (2N7000), Q16 (PN2222A), Q18 (J310)
Q19 (J310, Q20 (2N7000), Q24 (J310) Q25 (PN2222A) and Q21 (2N5109)

Install star heat sink on Q22 (2N5109) first
Then install Q22 with heat sink flush with PCB.

Install capacitor C167 (.001uf). preform legs


# # 04 MAR # #


Install capacitors

C86 (0.1uf), C84 (120pf), C85 (120pf)
C100 (.001uf), C95 (.01uf), C96 (1uf)
C71 (82pf), C72 (270pf), C73 (47pf), C74 (20pf)

C82 (.001uf), C80 (.001uf), C81 (.001uf)
C79 (.001uf), C59 (0.1uf), C38 (.001uf)
C55 (.01uf), C61 (.01uf), C58 (.01uf)
C65 (0.1uf), C54 (.01uf)

C68 (10pf), C64 (.001uf), C67 (0.1uf)
C63 (.01uf) C92 (.022uf), C94 (.047uf)
C89 (.001uf), C87 (.01uf), C175 (.01uf)
C62 (.01uf), C154 (100pf), C144 (100pf)

C156 (.047uf), C158 (.01uf), C53 (.01uf)
C52 (.01uf), C141 (.01uf), C57 (.001uf)
C146 (146uf), C151 (0.1uf), C145 (.01uf)
C153 (68pf), C155 (.01uf), C172 (.01uf)

C177 (.022uf), C174 (82pf), C173 (220pf)
C178 (0.1uf), C176 (0.1uf), C165 (.01uf)
C169 (390pf), C168 (.01uf), C160 (.01uf)
C159 (.01uf), C143 (.01uf), C142 (.01uf)

C163 (.01uf), C162 (.047uf), C164 (.01uf)
C170 (.047uf), C166 (.047uf), C179 (100pf)
C182 (180pf), C184 (.01uf), C185 (0.1uf), C181 (.01uf)

Install ICs
U6 (LMC662), U5 (LTC1451), U4 (MC145170), U3 (LT1252)
U10 (NE612), U9 (LT1252 ), U11 (NE612), U12 (MC1350)


# # 06 MAR # #


Install Voltage Regulator U8 (78L05)

Install Option-bypass jumpers W5, W2 and W3, use component leads

Install single pin test pointsTP1, TP2 and TP3

Install RFC 13 (100uh RF choke)

Install receive mixer Z6 (TOP-1)

Install electrolytic capacitors C60 (100uf) and C93 (10uf)

Install electrolytic capacitor C102 (220uf)

ON THE BOTTOM OF PCB locate U4 (MC145170). Install C88 (68pf)
on pins 13 and 12. Install RFC 15 (100uh RF choke) on pin 16 and adjacent trace.
Install capacitor C91 (.001uf) on pin16 also and adjacent pad.

DO NOT ALLOW CONTACT WITH OTHER TRACES.
A LITTLE ELECTRICAL TAPE INSURES NO CONTACT.


# # 07 MAR # #

Install crystal X1 (12.096mhz)

Ground crystal on top of case.

Install crystals X3 and X4 (4.9152mhz)

Ground crystals on top of case.

Install crystals X5 and X6 (4.936mhz)

Ground crystals on top of case.

Install crystals X7, X8, X9, X10 and X11 (4.9136mhz)

Ground crystal on both sides of cases.

Install RFC14 vertically

Install RFC 16 verically

Install RFC 11 horizonally

On the BOTTOM of PCB

Install toroidal transformer T5 horizonally

Using Nylon hardware in the synthezier area

Install toroidal transformer T7 horizonally

Install toroidal transformer T6 vertically.

Install slug-tuned inductors L30 and L34 (4.7uh)

Install capacitors C39 (.001uf), C4 (820pf), C5 (100pf)
C9 (.001uf), C7 (100pf)

Install capacitor C8 (820pf), C108 (.01uf)
W6 (option bypass), diodes D1 (1N4007), D2 (1N4007)
Resistor R38 (1K ohms), choke RFC (100uh)

Install capacitors C107 (.01uf), C109 (.01uf), C110 (.01uf)
Install diodes D3 (1N4007), D5 ((1N4007), D4 (1N4007)
Install resistor R37 (100K ohms), R39 (1Kohms)
Install capacitors C113 (.01uf), C114 (.01uf)
install W1 (option bypass)


# # 13 MAR # #

Install Q2 (ZVN4424A). It is flat on both sides
The WIDER flat side must be aligned with the flat
side of the component outline. RECHECK BEFORE SOLDERING

Install RFC 3 (FT37-43 16t). Install vertically

Install L1 and L2 (slug-tuned inductors)

Install 40 meter low pass components
capacitors C225 (390pf), C 228 (56pf)
C227 (330pf), C226 (680pf), C229 (220pf)

Install inductors L25 (T44-2 14t) and L26 (T44-2 12t)


# # 14 MAR # #

Install on the BOTTOM of the PCB
Some component leads may need to be pre-trimmed before soldering

Install capacitors C207 (.001uf), C216 (.001uf), C223 (.001uf)
C224 (.047uf bend body down before soldering),
C204 (.001uf), C208 (.001uf), C195 (.001uf)
C133 (0.1uf bend body down before soldering),
C135 (.01uf), C122 (56pf), C119 (.01uf), C17 (.001uf)
C27 (.001uf), C104 (68pf), C29 (12pf), C28 (12pf)

Install resistor R34 (2.7K ohms)
Install chokes RFC2 100uh) and RFC7 (15uh)

Install capacitor C6 (4.7pf) center hole note used)

Install shielded solenoidal inductor L31 (12uh)

Install capacitors C183 (.01uf), C186 (.01uf), C161 (.01uf), C150 (330pf)
C90 .047uf) and C157 (.047uf) bend the bodies down before soldering),

Install resistors on bottom of PCB
R77 (220 ohms), R76 (10 ohms), R75 (680 ohms), R94 (82 ohms)
R99 (270 ohms), R98 (270 ohms), R100 (820 ohms), R110 (5.6K ohms)
R114 (3.9K ohms), R18 (1M ohms), R29 (10K ohms), R19 2.7K ohms)
Install choke RFC 12 (100uh) and RFC10 (1mH)

Install diode D36 (BAP-64-05 daughterboard)
pin one not used. pin3 goes to banded end of outline

BFO TOROID L33 INSTALLATION. Locate rubber stem bumper
Cut top half off. Mount prewound toroid core on bumper

Mount resister R116 (5.1mM ohms) on top of core
Attached toroid leads R116 to either side. Top lead to the
left bottom lead to the right. Caution the leads are fragile

Install diodes D40 and D41 (1N4148) to the two round pads
to the right of resistor R114. Banded ends go in opposite directions

Perform resistance checks

This concludes Assembly Part II
Resistance check almost identical to K2 #6321 from 10 years past.


# # 15 MAR # #

Now to assemble case to perform
Alignment and Test Part II

A full view so you can see what remains

Attach the sides

Attach the front panel

Install the control board to the front panel

A layer of electrical tape on the bottom inside cover
too prevent case contact with the BFO

Attach the bottom cover


# # 25 MAR # #

Now its Alignment and Test Part II

4Mhz oscillator Calibration

4Mhz Oscillator Calibration completed.
External counter reads 12.099.02mhz.Last digit flickers
K2 reads 12.099.03mhz. Close as I can get.

PLL Reference Oscillator Range test

Range should be between 12080-1290Khz
C84 and C85 had 12PF (120) CAPACITORS they were replaced
with 120pf (121) capacitors which it should have been.
Hi reading now is 12099.52
Lo reading now is 12086.13
diff is 13.39 this range is acceptable

VCO (Voltage Controlled Oscillator) Test

Frequency should be be between 8 and 10Mhz
Measured reading was 11.869.53
Checking the circuit I found a wrong value capacitor
Replaced with correct value. Now frequency is 8.913.26mhz
This is acceptable

VCO Alignment

VCO Voltage Readings
Per Band reading must be
>= 1.5VDC on the low the end
and <= 7.5VDC on the high end.
Compressing/expanding the windings of T5 adjusting inductor L30
Increasing the padding capacitor value on C172 is sometimes required.
-----------------------------------------
Final VCO Voltage reading
-------------------------------------------
80M---LO FREQ--1.79__HI---6.34
40M---LO FREQ---2.39__HI---4.60
30M---LO FREQ---4.34__HI---5.11
20M---LO FREQ---2.56__HI---4.26
17M ---LO FREQ---3.24__HI---3.44
15M---LO FREQ---3.38__HI---4.97
12M--LO FREQ---4.21__HI---4.61
10M--LO FREQ---3.41__HI--4.29
BFO Test
C169 HAS BEEN REPLACED WITH CORRECT VALUE
read 4913.59
BFO HI---4917.56
BFO LO---4911.94
RANGE= 5.62KHZ (must be >=3.62khz)
Isn't it odd how well it works with correct values?

BFO Alignment
Completed

VFO Linearization
Completed no issues

I.F. Alignment
Completed

40 Meter Band Pass Filter
Completed


# # 26 MAR # #

Assembly Part III

Install resistors R46 (270 ohms), R45 (47 ohms), R59 (4.7K ohms)
R61 (120 ohms), R49 (120 ohms), R40 (470 ohms), R41 (560 ohms)
R55 (33 ohms), R53 (4.7 ohms), R56 (33 ohms), R54 (4.7 ohms)
R60 (100 ohms), R62 (2.7K ohms), R67 (1.5K ohms), R68 (226 ohms)

Looks like the last of top mounted resistors.


# # 27 MAR # #

Install capacitors C12 (560pf), C11 (180pf), C26 (.001uf)
C16 (1800pf), C15 (560pf), C22 (3.3pf), C20 (47pf),
C19 (330pf), C30 (470pf), C24 (47pf), C25 (330pf),
C35 (56pf), C37 (.001uf), C36 (470pf, C33 (2.2pf)

Install capacitors C49 (.01uf), C31 (56pf), C42 (330pf)
C43 (33pf), C48 (330pf), C47 (33pf), C45 (1pf), C115 (.01uf)
C117 (.047uf), C118 (.01uf), C116 (33pf), C121 (.01uf)
C120 (.01uf), C131 (0.1uf), C124 (0.1uf), C130 (0.1uf), C128 (680pf)

Install capacitors C129 (.01uf), C127 (680pf), C191 (1800pf)
C190 (1200pf), C197 (100pf), C198 (27pf) C210 (82pf), C211 (10pf)
C218 (150pf), C219 (12pf), C138 (.047uf) C222 (100pf), C221 (39pf)
C220 (220pf), C214 (68pf), C213 (33pf), C212 (150pf), C203 (47pf)
C199 (220pf), C200 (150pf) C202 (120pf)C201 (220pf), C192 (1200pf)

Looks like the last of the top side mounted capacitors.


# # 28 MAR # #

Install (10-50pf) Trimmer Capacitors at C21, C23, C32 and C35
Install (20-50pf) Trimmer Capacitors at C44, and C46

Install RF choke L5 (33uH)

Install transistor Q10 (2N7000). Q11 (PN2222A) and Q13 (PN2222A)

Install Ferrite bead assembly vertically at Z1


# # 29 MAR # #

Install Diode D9 (1N5711)

Install electrolytic capacitors C126 (47uf) and C137 (100uf)

Install electrolytic capacitor C125 (22uf)

Install transistor Q5 (2N5109)

On the BOTTOM of the PCB
Install resistor R63 (220 ohms)

Install resistor R58 (180 ohms)

Install (10uH) RF chokes at RFC8, RFC9, RFC4 and RFC 6 (.68Uh)

Install RF choke RFC5 (10Uh)

Install resistor R50 (1.5 ohms)

Install resistors R48 (420 ohms), R47 (47 ohms)
R43 (22 ohms), R42 (4.7 ohms), R44 (2.7K ohms)

The last of the BOTTOM side components have been installed
Except for the power amplifier and heat sinking components.

(L) bottom view (R) top view


# # 30 MAR # #

Install slug-tuned 4.7uH inductors at L3, L4, L8 and L9

Install slug-tuned 1uH inductors at L10, L11, L12 and L13

Install self-adhevise pad on the Q6 outline

Install transistor Q6 (2SC2166) on the Q6 pad


# # 31 MAR # #

Wind and installL16 (T44-2-21t), L17 (T44-2-21t)
L18 (T44-2-9t), L19 (T44-28t), L20 (T44-2-7t

Wind and install L21 (T44-10-9t), L22 (T44-10-8t)
L23 (T44-10-11t), L24 (T44-10-10t)

Wind and install toriodal transformer T1 (FT37-43/p-9/s-3)

Wind and install toroidal transformer T2 (FT37-43/p-12/s-8)

Wind and install vertically T3 (FT50-43-5t). A bifilar winding (two wires twisted together) Then wound on the core.

Toroid transformer T4 is mounted on top of the screws that attach the "D" connector
Check that they are tight. The must never loosen

Winding #1 is 2 turns of green hook-up wire on a binocular core.
Winding #2 is 3 turns of white hook-up wire on top of the green winding
Winding #3 is a bare wire through one side of the core only
Winding #4 is a bare wire through the other side only

The mounted transformer MUST BE PARALLEL to the PCB and inside the outline before soldering.


# # 1 APR # #

PA transistors Q7 and Q8 (2SC1969) must be installed on the BOTTOM of the PCB

Bend the leads UP AWAY FROM THE TABS

Attach Q& & Q8 using 1/2" 4-40 screws a #4 fibre washer 1/4 phenolic standoff
and #4 sholder washer which act as insulation against grounding the collectors

using 4-40 nuts and #4 lock washer finger tightened only.

Check AND VERIFY Uninstalled components lists.

Install P6 from the KAT2 option

Perform resistance checks

Passed resistance checks

Install side panels

Install Front Panel

Install bottom cover

Install Control Panel

Check the panel fully seated

Place self-adhesive thermal pads on top of Q7 & Q8
The pad must fully cover the transistors tabs to prevent
shorting to ground

Install rear feet to the BOTTOM REAR PANEL before
securing Q7 and Q8 to the bottom rear panel (It is a heat sink)

PERFORM A RESISTANCE CHECK FROM Q7 & Q8 COLLECTORS TO GROUND

NO SHORTS TO GROUND (G)


~ ~ ~

ALIGNMENT AND TEST, PART III

08 MAY 2018

Set power switch to OFF position (OUT)
DONE
Connect power supply /battery that will handle at least 2 AMPS
DONE
Connect 50 ohm Dummy load rated for at least 10 watts
DONE
Turn on K2. Shold see ELECRAFT then the FREQUENCY
DONE
select voltage/current display mode by tapping DISPLAY to
make sure the receiver is not drawing excess current
(Typical current drain will be 180-250ma depending on menu setting)

DISPLAY SHOWES E12.0 i 020 (12VDC @ 200 MA)

Return to frequency display mode
Switch to CW ans select FL1 uning XFIL DONE
Set CW sidetone volume and pitch using ST L and ST P.
DONE
Set desired keying device using INP in menu
DONE
Verify that sidetone is functioning by holding the SPOT switch
DONE
40-Meter Transmitter ALIGNMENT

Set POWER control for 2 watts
Switch to 40 meter band and set VFO for about 7100kHz
Locate L1 and L2
Put the K2 in TUNE mode
While in TUNE adjust L1 for max power. Tap any switch to exit
While in TUNE adjust L2 for max power. Tap any switch to exit
Repeat previous steps several to confirm max power
IF YOU CANNOT GET POWER OUTPUT TO 2.WATTS OR HIGHER SEE TROUBLESHOOTING

Power out does not exceed 0.900mw

ALIGNMENT AND TEST, PART III
SIGNAL TRACING TO FIND THE ISSUE OF LOW POWER OUT
USING AN RF PROBE AND DMM

11 MAY 2018

PLL REFERENCE OSCILLATOR and VCO

REFERENCE OSCILLATOR OUTPUT:

Measure the reference oscillator signal ap
pin 1 of U4 (MC145170). Expected 0.8-1.8 Vrms
actual:
0.857Vrms

VCO OUPUT:

Measure the VCO signal at
pin 3 of U3 (LT1252). Expected: 0.30-0.40Vrms.
actual:
0.327Vrms

VCO Buffer Output:

Measure the signal on pin 6 of U3
Expected 0.60-0.75 Vrms
actual:
0.684Vrms

BFO Output:
Measure the signal on pin 6 OF U11 (NE602)
Expected 0.20-0.70Vrms
actual:
0.508Vrms

Use menu to select CAL FCTR
Measure the amplitude of the signal at TP2
Expected: 0.025-0.070 Vrms actual:
0.034 Vrms

EXIT CAL FCTR

30 JUNE 2018

THE FINAL ASSEMBLY

this was completed before sending it off for repair. on Sep 1st

Place the top cover upside down. Trim the grill cloth to the speaker fram size.
Use #4 fibre washers with 3/8" (9.5mm) screws and #4 lock washer and 4-40 nuts. DO NOT OVER TIGHTEN

Install 2D fasteners

Remove .5" X .5" square of masking material covering
EXT SPKR hole. Install external speaker jack

Cut the the 24" of speaker cable into two pieces. One 15" and the other 9"
Solder crimp pins to one end ofthe 15" scetion. Insert copper wire in Pin1 position

The remaining wire is inserted in position 2

The other end of the speaker wire is attached EXT SPKR jack.
The copper is attached to the AF position. The other wire will be grounded
DO NOT SOLDER YET

Connect the 9" speaker wilre to the speaker.
The Copper wire is attached to the "+" terminal
Attach the other end to the EXT SPKR jack
The copper wire is attached to the SP terminal
The other is grounded. Solder all three connections

Use cable ties to hold the wires in place.

Leave the frequency counter test cable connected to the BFO test point (TP2)

Plug the speaker cable into P5

Attach the serial number to the rear panel. Write the serial number on the manual.

ACTUAL CONSTRUCTION OF THIS BASIC K2 SER#7750 IS COMPLETE
THE OPTIONS TO BE INSTALLED AFTER CHECK OUT OF K2 #7750

I knew I was really out of my league on this
When it came to finding the issues
So I sent it to an expert technician
Alan D. Wilcox, W3DVX

I waited SOME TIME before shipping
shipped it on 1 Sep 2018
Work done on radio K2 #7750:
Built, installed, tested KIO2.
Found and did he following Repairs:
Replaced broken RFC10;
corrected Z1-Z2 construction;
corrected C72;
fixed solder-blob short at RP2-8;
T4 was installed backwards; checked,
reflowed toroids T1, T2, T3; repositioned encoder,
smoothed connections,
insulated; TR switch
D3 was reversed;
soldered missed connections, touched up others.
FL1-FL4 not working: resoldered T7 and other filter parts.
Flickering right-side LED in front display:
repositioned the LED slightly,
and that seems to have fixed problem,
although it might be heat sensitive.
Tuned up the K2 including all the BFO settings for 600 Hz.
Set the frequency calibration better than 20 Hz at 10 MHz,
although it needs to warm up a bit.
Peaked the BPF filters for max power output.
returned to me on
13 Sep 2018

The KIO2 COMPUTER INTERFACE

KC5WA IS NOW WW5RC

AND A KIT BUILDING ADDICT