Hal Communications MKB-1 User manual

May 28, 2023
HAL Communications MKB-1 Morse Keyboard and HAL ID1 Kit.
I purchased this keyboard at the Charlotte Hamfest. It did not work when I tested it. I could not find
information about it so I wrote to Motorola Solutions. They own HAL now. After a few days, they sent
me an instruction manual. The manual has the theory of operation and a schematic.
I tried to find out why my keyboard did not work. I measured the voltages in the circuit board and they
are all correct. After a while, I found that if I temporarily ground the gate of the 2N5062 SCR, the
keyboard would work. The SCR powers up disabled when it should be enabled.
In the theory of operation, there is an error on the bottom of page 5 and the top of page 6. It says
“…….the SCR to fire and a current pulse to flow…….”. The SCR does not fire to generate a pulse. The SCR
has to be on when the keyboard is waiting for a key to be pushed. While it is on, there is 5.3 volts on the
wires to the keyboard. When a key is pushed, one of the wires is grounded causing current to flow in the
toroid cores. Immediately the SCR is turned off disabling any additional keyboard input. After the Morse
character is sent, the SCR is enabled. This provides 5.3 volts to the keyboard and be ready for the next
character.
In my keyboard, I am unable to find out why the SCR is powering up in the disabled state. The only
memory in the keyboard are the four 7474 flip-flops. They are all correct after power up.
There is a wire from the gate of the SCR to a key on the bottom left of the keyboard. That key is not
marked. When it is pushed the gate of the SCR is temporarily grounded. After that the keyboard works.
On the schematic, the wire is marked KB-ID Clear. When this key is pushed after power on, “H2MYG” is
sent. It must have something to do with the KB-ID1. I labeled it “Reset”.
This keyboard has an optional HAL KB-ID1 circuit board. When the “Here Is” key is pressed, it sends DE
followed by a call sign. If the “Here Is” key is released before the call sign starts, only DE is sent. The key
has to be held down until the call sign starts for the call to be sent. When the key is used “DE K2MYG” is
sent. The unmarked key above the CQ key sends 73 when pushed.
The Weight control was way out of range. It had to be set at the extreme end of its rotation for the
characters to be close to correct. Therefore, I disabled it by connecting a 56-ohm resistor in place of it.
Now when a five is sent, the dot length is the same as the space between each dot.
The output transistor 2N5655 can handle 250 volts at 0.5 amps.
The range of the speed control is six to 53 wpm.
73 Tom N4TL
In the combined PDF, Page 1 is this page.
Pages 2 to 41 are the HAL MKB-1 Instruction manual.
Pages 42 to 62 are the HAL ID1 Kit instructions.

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WARRANTY
IIAL Communications Corporation \^Iarrants that all factory-
assembled MIG-1 lulorse Keyboards sha11 be free of defects in
materials and workmanship under normal use and service for a
period of one year from the date of the original invoice, and
further warrants that all parts supplied with MKB-1 kits sha11
likewise be free of such defects for the same period.
Should such defects occur within the warranty period, notify
IIAL Communications Corp. promptly in writing. The
notification letter must be postmarked prior to one year
from the date of the original invoice. Please do not return
your unit to the factory for repair until you have sent a
letter of notification and have received a written return
authori zatLon.
Keyboards or parts returned to the factory under warranty
will be repaired or replaced at no charge except for
transportation costs.
This warranty is and shatt be in lieu of all other
warranties, whether expressed or implied, and of all other
obligations or liabilities on the part of IIAL Communications
Corp. resulting from the installation or use of this keyboard.
The foregoing warranty is completely void i" all keyboards
which have been damaged, abused, modified, or improperly
installed or operated.
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Copyright @ L973 by IIAL Communications Corp., Urbana,
Iltinois. Printed in the U.S.A. A11 right reserved.
Contents of this publication may not be reproduced in any
form without the written permission of the copyright owner.

1.
2.
3.
4.
5.
6.
7.
8.
Figure
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4 .3:
4 .4:
5.1:
5 .2:
5.3:
5,42
5.5
5,6
7,L
7.2
7,32
7 ,42
7.52
CONTEM S
Introduction . . . . . . . . . . . . . . . . . .
Installation........o...
OperatingYourKeyboard .. ..
Theory of Operation
Construction
Testing and
Diagrams andT rouble shoot ing
Photographs....
Parts List
ILLUST RAT IONS
1
2
4
5
13
29
31
37
10
L4
16
20,21
Typical Connection for C
TypicaL Connection for G
Shift Register Operation
C lock lrlavef orms
Logic Waveforms
Logic Waveforms
Component Layout
Keyswitch Board
athode Keying . .
rid-B1ock Keying
for Letter rrRrr
....7
for Letter rrHrr . . 10
3
3
7
for Letter rrRrr
Logic Circuit Board
Layout
ToroidMounting . . . . . . .. . . . . . . L7
Winding the Toroid Secondaries . . L7
ToroidWiring .... .. L7
RearandTopPanelPartsPlacement. .. .... 22
MKB-1 Schematic Diagram . . 32
Photograph of Assembted Logic Circuit Board . . . . 33
PhotographofAssembledKeyswitchBoard.... .. 34
Photograph of Cabinet-to-Circuit Board Connections . . . . 35
Photographof Completedl,ll(B-l .... .. .. 36
TABLE
Table 5 . 1: Toroid I^Iiring

I. INTRODUCf,ION
The HAL MKB-1 is a completely self-contained morse code keyboard. Pressing
the keyswitch for any character automatically produces the proper sequence
of dots and dashes needed to transmit the character. By means of an internal
transistor switch, the MKB-1 can key a transmitter directly. A sidetone
monitor and speaker are included.
The MKB-1 combines digitat and linear circuitry to provide the following
features:
Code speed is adjustabte from 6 to 60 words per miSute.
Adjustabte weight ratio is unaffected by changes in speed.
Connection for auxiliary hand key is provided.
Transistor switch can be connected for either grid-block or
cathode keying.
The logic circuitry and power supply are built on a single 3 X 6 inch printed
circuit board, through-plated so that all soldering is done on one side of
the board. The keyboard and toroidal keyencoder mount on a 5 X 11 inch
board. The complete unit including power supply is housed in an attractive
sloping panel cabinet.

The I'{IG-l is simple
outlet. A hand key
The keyboard audio
audio amplifier or
2. INSTALLATION
to install. Connect the line cord to a 115 vAC, 60 Hz
may be connected to Jl on the rear panel if desired.
is available at J3 and may be used to drive an external
sma11 speaker.
The transistor keying switch in the MKB-1 may be used for either cathode
or grid-block keying, depending on which of the two rear-pane1 jacks is used.
The thTo jacks may not be used simultaneously, however.
For cathode keying, the transistor switch is inserted in series with the
cathode circuit of the stage to be keyed. Connect the cathode lead to the
tip contact of a phone plug using the center conductor of a length of
shielded wire. Ground the shield braid at the transmitter. Plug in the (+)
CATHODE jack on the rear panel of the MKB-I. A typical installation is
shornrn in Figure 2.L.
NOTE: The transistor keying switch is rated to handte +250
volts at up to 100 ma. Before connecting the keyboard
to the transmitter, make certain that the voltage and
current at the keying point in the transmitter do not
exceed these values,
For grid-b1ock keying, the transistor switch shorts the grid bias voltage
to ground. Using the center conductor of a shielded cable, connect the bias
voltage to be keyed to the tip contact of a phone p1ug. Ground the shield
at the transmitter and connect it to the sleeve of the phone plug. Insert
the plug in the (-) GRID jack on the rear panel of the MKB-I. Figure 2.2
shows a typical hookup.
NOTE: The transistor switch is rated to handle -150 volts at
up to 100 rr8. Check the voltage and current at the
transmitter keying point to ensure that these values
are not exceeded.
CAIIIION: Some transmitters (such as the y""lu FTDX-560 and several of the
Swan transceivers) provide a wave-shaping filter in the key 1ine, with a
high-value capacitor (on the order of 0.1 ufd) connected directly across the
key terminals. The charge stored in this capacitor can produce a current
surge large enough to destroy the keyboardrs switching transistor when the
transmitter is keyed. Check the schematic diagram of your transmitter to
determine whether such a capacitor is present, If so, insert a |-watt
resistor (of any vatue between 100 and 390 ohms) in series with the keying
line. Use the highest vaLue that does not affect the transmitter keying.
The resistor can be mounted conveniently inside the phone plug used to
connect the transmitter to the MKB-1 keying jack.

TYPICAL
CATHODE
CON N ECTION
TO KEYING
TRANSISTOR
COLLECTOR
TO KEYING
TRANSISTOR
EM ITTER
+
= :
TRANSMITTER
Figure 2.1 Typicol Connection for Cothode Keying
E NOT USE CATHODE AND
GRID BLOCK AT SAME TIME
Figure 2.2 Typicol Connection for Grid -Block Keying
TYPICAL
GRID BLOCK
CON N ECTION
_l_
-l
TRANSM ITTER
CATHODE
GRID BLOCK

OPEMTING YOUR KEYBOARD
The I"IKB-1 operates very much like a standard typewriter. After a short
practice period, sending code will be as easy as typing. It will be helpful
to practice with the keyboard alone, listening to the code signal from the
sidetone monitor, before using the unit on the air.
To turn the keyboard oD, rotate the volume control clockwise. Touch one of
the keys and adjust the volume and tone controls for a pleasing sound from
the sidetone monitor.
Rotate the speed control fully counterclockwise to the slowest code speed.
Practice typing until you get the "feel" of the keyboard; then gradually
increase the speed as you type. The weight control may be adjusted to
achieve the desired ratio of dot-to-space duration.
The following tips will help you become proficient at codetyping:
The code character produced by any key will repeat conLinuously
as long as you hold the key down. To send the character only
oncer release the key before the character has been completed.
For best performance when sending a string of characters, push
the first key and hold it momentarily until the character has
started. Then press the next key and hold it until the first
character completes and the second character starts. Proceed
to the third key, and so on. Using this method will ensure
that--there are no unduly long gaps between characters and that
no character wiLl be omitted.
3.
The tune key parallels the external
it keys the transmitter for tuning.
on as long as the key is held down.
hand key input. Depressing
The transmitter will stay

T}MORY OF OPEMTION
The basic function of the I,IKB-1 circuitry is to translate a keystroke into
the sequence of dots and dashes needed to transmit a Morse code character.
A transistor switch is included to key an external transmitter. The keyboard
also activates a sidetone oscillator to permit monitoring of the code
characters transmitted.
The circuit consists of five basic sections: a ctock oscillator, a shift
register, a character generator, the keying stage with sidetone oscillator,
and a regulated power supply. A schematic of the I"IKB-I is shown in
Figure 7.L (page 32).
A shift register is used to transform each keystroke into a sequential binary
code. When one of the character keys is pushed, the binary code for that
character is loaded into the shift register through a toroid matrix at the
registerts paratlel input terminals. The clock oscillator then starts,
causing the contents of the register to appear sequentially at the register
output terminal. This output is combined in the character generator with
pulses from the clock oscillator, producing the series of dots and dashes
required to transmit the character. The character generator output controls
a transmitter keying transistor, and it also activates the audio sidetone
oscillator.
Character Shift Register
The shift register consists of seven integrated-circuit flip-f1ops connected
so that the state of each flip-flop will transfer to the next flip-flop in
the line whenever a dot or dash is compteted. The clock terminals of the
flip-flops are connected in paratlel so that all receive shift putses
s imultaneous ly.
Initially, all of the flip-flops are in the trtrr state; that is, the a output
(pin 5 or 9) is high. Some of the ftip-flops are cleared (set to the low or
zero state) by the keyswitch closure, depending on the code character to be
produced, As shift pulses are received, the regitter contents appear in
sequence at the output of the last flip-flop. This sequential binary code
is fed to the character generator. If the register output is low during a
given clock pulse, a dot will be produced. If it is high, a dash results.
Because each key represents a different character, each must load a unique
binary code into the register, Closure of a given keyswitch must result in
some of the flip-flops being left in the high state and others being cleared
to the low state. Consequently, each keyswitch must be isolated from all
the others. This isolation is provided by the seven toroidal transformers,
whose secondary windings are connected between the flip-ftop ctear terminals
and the +5 volt supply.
The toroids have a number of primary trwindinBstt, each of which consists of
a length of wire connected from the 2N5062 silicon controlled rectifier
(SCR) to a keyswitch. VJhen the keyswitch is ctosed, it grounds the wire,
4.

causing the SCR to fire and a current puLse to flow in the wire. The wire
Passes through the toroids of those flip-flops which must be cleared. The
pulse induces a negative-going secondary vottage large enough to drive the
flip-flop clear input to zero and to reset the ftip-flop. The binary code
corresponding to the characterrs pattern of dots and dashes is thus loaded
into the shift register.
As an example of how the shift register works, consider the transmission of
the letter rrRrr (dot-dash-dot). The wire from the R keyswitch to the SCR
Passes through the toroids connected to flip-flops FFO, FF2, and FF3. When
the keyswitch is closed momentarily, these flip-flops are cleared and their
outputs go to the zero state. A11 of the other flip-flops remain in the high
state, 8s shown in Figure 4,La.
The R keyswitch clears flip-flop FFO so that its output is tow, since it will
produce the first dot. It does not affect the second ftip-flop, FFl, because
the second character will be a dash. However, it ctears the third flip-flop,
FF2, to produce the final dot, The fourth flip-flop, FF3, is also reset to
produce a space at the end of the character, as will be explained later.
After the flip-flops are set to the proper states, the clock oscillator
starts and the character generator produces its first output pulse. Since
the output of the shift register is low, the pulse is short: a dot, At the
end of the dot, the state of each flip-flop shifts one stage to the right.
FFO is now in the high state, FF1 and FF2 are in the low state, and the
remainder are in the high state. Since the data input to FF6 is tied to the
+5 volt bus, this flip-flop remains in the high state. The register contents
are now as shown in Figure 4.Lb. When the next clock pulse occurs, the high
leve1 at the register output results in the production of a dash, and the
register contents again shift one stage to the right.
Each time the register contents shift, a trlrr is again read into FF6, and
the former rrlrr code is transferred to the next stage. After the second dot
has been sent, the register stages are therefore all set high except FFO.
This last zero output would normally produce a dot during the next clock
pu1se. A special gate, however, prevents the dot from being transmitted.
The inputs of TC7, which forms a NOR gate, i." connected. to the inverted
outputs of the register stages. !,lith all of its inputs low, the NOR gate
output bus witl be high. This signal is fed through an inverter to the
input of a NAND gate (pin 13 of IC5) in the character generator, driving it
1ow. The NAND gate output therefore must remain high regardless of the
character generator output state. Although the character generator produces
a dot, the gate prevents its output from reaching the keying transistor and
sidetone oscillator. This feature provides an intercharacter space between
the completion of one letter and the beginning of the next one.
Clock Oscillator
Timing for the keyboard circuits is provided by the clock oscillator, which
consists of an operational amplifier (IC2), a monostable multivibrator (IC3),
two transistors, a triming capacitor, and the speed control.

+5V
(o ) Reg ister Contents of ter Chorocter rr Rrr is Looded
REGISTER
OUTPUT
REG ISTER
OUTPUT
SHIFT
INPUT
(b) Register Contents ofter Completion of First Dot
Figure 4. ! Shif t Register Operotion for Letter rr R rr
(o ) Oscillotor
Out put
( b) Weisht
Detector
Output
TH RESHOLD
LEVEL
F igure 4.2 Clock Woveforms

trlhen the osci llator is quiescent, the
pin 3 of the operational amplifier is
inverting input, is therefore held at
inverting input, pin 2, is held at +5
amplifier output is negative.
4.7 pfd timing capacitor connected to
partially charged. Pin 3, the non-
a positive voltage. Because the
volts by the clock keying line, the
To start the oscillator, the clock keying line is driven toward ground.
The amptifier output goes high, triggering the monostable to produce a short
pulse. This pulse is shifted in Ieve1 by the I'1PS3703 transistor and is fed
to the base of a MPS3395 transistor connected across the timing caPacitor
terminals. During the monostablefs output putse, the transistors conduct
and the capacitor is discharged. Pin 3 of the amplifier is driven to -6 volts
and the amplifier outpuE goes negative.
At the end of the monostable pulse, the MPS3395 ceases to conduct and the
capacitor begins to charge through the speed control potentiometer. When
the capacitorrs positive terminal exceeds the voltage on pin 2 of the op
dmpr the amptifier output again goes high and the cycle is repeated. The
oscillator output, a sar^rtooth wave, appears across the timing capacitor,
The frequency is adjusted by the speed control, which determines the
charging time of the capacitor.
The oscillator keying line is driven by the outputs of TC7. When one of the
keyswitches is closed, one or more of the shift register flip-flops is
cleared, and the output of TC7 goes low. This signal is fed to a NAI{D
gate (pin 5 of IC5) and then through an inverter to the keying line. The
output of the NAND gate goes high, the inverter output goes to zero, and
the oscillator starts. A connection from flip-flop FFO to a second input
of the NAND gate (pi, 4 of IC5) ensures that the clock keying line will be
held low and that the clock oscillator will be kept running while the
intercharacter space is produced. After the space is completed, the
register contents are shifted once more. A11 stages are then high and both
inputs to the NAND gate are high. The keying line goes high and the
oscillator stops until the next keystroke.
The clock keying line also drives the gate *terminal of the SCR. For the
SCR to fire, one of the keyswitches must be closed, providing a path for
the anode current, and the gate terminal must have a positive potential
applied to it. While a character is being produced, the keying line is
held low and the SCR cannot fire, The keyboard is therefore I'locked outrr--
closing one of the keyswitches wilL have no effect on the contents of the
shift register until the character is completed and the keying line goes
high again. Holding a key down will cause the character to repeat, since
the SCR will refire as soon as the character is transmitted and the clock
line has gone high.
Character Generator
the character generator, where
the character shift register to
make up each character.
Putses from the clock
they are combined roith
produce the series of
oscillator are fed'to
the binary code from
dots and dashes which

The clock pulses drive a weight detector, composed of a 741 operational
amplifier operated in the open loop (maximum gain) configuration. A reference
or threshold voltage, controlled by the weight potentiometer, is applied to
the amplifierrs non-inverting terminal (pi, 3); the sawtooth output of the
clock oscillator drives the inverting input (pin 2). When the clock signal
is more positive than the threshold voltage, the amplifier output is negative;
when the clock is negative with respect to the threshold leve1, the output
becomes positive. Thus the sawtooth input \^Taveform of Figure 4.2a is con-
verted to a rectangular wave, 3s shown in Figure 4.2b. The ratio of the
time during which the output is positive to that during which it is negative
determines the "weight" (dot-to-space ratio) of the transmitted code, and may
be adjusted by changing the threshold voltage with the weight control.
The weight detector output drives a Schmitt trigger, composed of two inverters
(IC4). This circuit converts the weight detector output to a voltage leve1
suitable to trigger the dash flip-flop. The Schmitt trigger output drives the
clock input of the flip-flop. An inverted output is taken from pin 8 of IC4.
The direct clear terminal of the dash flip-flop (pin 13) is conrrolled by rhe
output of the shift register. VJhen this terminal is held low, the flip-flop
is prevented from changing states; the output from pin 8 remains high. When
the clear terminal is high, the flip-flop toggles at the beginning of each
positive clock pu1se.
Wtren a key has been pushed and a character code loaded into the shift
register, the clock oscillator starts, as previously described. Assume for
the moment that the character to be produced is an rrHrr--four dots followed
by an intercharacter space. The first five fiip-flops in the shift register
will be set to the zero state.
Immediately after the key is pushed, a positive clock pulse is produced, as
shown in Figure 4.3a. The inverted clock pulse from the Schmitt trigger
(Figure 4.3b) is supplied to pirr 1 of NAND gate IC5, which goes low. The
clear terminal of the dash flip-flop (Figure 4.3c) is held 1ow by rhe shift
register output, so the dash flip-flop output, fed to pin 2 of IC5, remains
high (Figure 4.3d). Since only one input of the NAI{D gate is high, the
output will also be high, producing the f ifst dot (Figure 4.3e) . Inlhen the
inverted Schmitt trigger output goes high at the tnd of the clock pulse, the
NAND gate output goes 1ow, producing a short space before the next dot,
This signal is fed through a second NAND gate and an inverter (pins 1 and 2
of IC6) to the keying srage.
At the end of the first dot, the clock terminals of the shift register
stages, driven by inverters from the first NAND gate output, Bo high,
causing the registerrs contents to shift one stage to the right.l Since
lrro inverters (pins 5, 6, L2, and 13 of rc4) are used to provide
sufficient current to drive all seven register clock terminals.

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the second code element stored in the register is also a zero, the shift
register output remains low. On the next clock pulse, the dash flip-flop
is again prevented from toggling and a second dot is generated. This
process is repeated until five dots have been produced. The last dot,
however, is suppressed. Each time the register shifts, flip-f1op FF6 is
set to the high stater 3s discussed previously. When stages one through
six are all high, the output of TC7 goes high. This signal passes through
an inverter to one input of a NAI{D gate (pin 13 of IC5). The output of the
character generator is applied to the gaters other input. With pin 13 held
low, the gate output (pin 11) cannot change state. Thus the final dot is
prevented from reaching the keyer stage.
Now consider the sequence of operations in generating the tetter rrRrt
(dot-dash-dot). After the R keyswitch is closed, the first register stage
contains a zero for the initial dot, the second remains high to produce a
dash, and the third and fourth are set to zero to create the final dot and
an intercharacter space. The logic sequence is shown in Figure 4,4.
I^lhen the oscillator starts, the f irst dot is produced as bef ore. The dash
flip-flop does not toggle at the beginning of the dot because its clear
terminal is held 1ow by the shift register output, However, when the
register contents shift at the end of the dot, the register output goes high.
The flip-flop output remains the same temporarily. At the beginning of the
next positive clock pu1se, however, the flip-flop toggles and its output
goes 1ow. With a low input to pin 2, the output of IC5 goes high for one
clock period. After the leading edge of the next clock pulse, the flip-flop
toggles again, its output returning to the high state. The NAND gate output
is held high now by the low input from the inverted clock pulse applied to
pin 1. At the end of the clock pulse, both inputs of the gate become high,
the output goes 1ow, and a short space is produced before the beginning of
the next clock pulse. The dash generated is three times as long as a dot.
At the end of the dash, the register contents shift once more, and the
third code element, a zero, appears at the output. During the next clock
pulse, a dot is produced. As with the character ttHtt, an extra dot is also
generated but suppressed to produce an inlrcharacter space.
The inverted output from the character generator'appears at pin 11 of IC5.
This terminal is tied in parallel with the hand key and the tune keyswitch,
and is connected to the input of an inverter (pin 1 of IC6). When either
of the contacts is closed or the NAND gate output is 1ow, the inverter
output becomes high, triggering the sidetone oscitlator and the keying
transistor.
Sidetone Oscillator
Portions of IC5 and IC6 are connected in a feedback arrangement to form an
audio oscillator for monitoring the transmitted code signal. When the
oscillator is quiescent, the input to pin 10 of NAND gate IC5 is 1ow,
allowing the gate output to go high. This signal is applied to an inverter
(pin 13 of IC6), forcing its output 1ow. The output is connected to one
terminal of the timing capacitor, a 2.2 pfd electrolytic, and to the input
11

of a second inverter. The latter
positive voltage through the tone
capacitor and to the second input
inverter output is high, apptying a
control to the other terminal of the
of the NAI{D gate.
tr{hen the oscillator is keyed by applying a high 1eve1 to pin 10 of IC5,
the NAND gate output goes 1ow, driving pin L2 of IC6 high and pin 8 low.
The capacitor discharges through the tone control until pin 9 of the NA\ID
gate approaches zero. The NAI{D gate output then goes high again, the
capacitor recharges, the output of IC5 is again driven low, and the cycle
repeats, The frequency of the oscillator is determined by the time constant
of the capacitor and tone control.
Output from the osclllator is taken from pin L2 of IC6 and fed through an
inverter to supply the current required to drive the speaker and an
external audio 1oad, Lf any.
Keving Stage
The transmitter to be keyed by the MKB-I is connected to either the cathode
keying or the grid-block keying jack. Current through these jacks is
controlled by a 2N5655 switching transistor. The keying signal from the
character generator, taken from pin 2 of IC6, drives the base of the keying
transistor through a 2N5401 connected as a common base amplifier.
Power Supplv
The +5 volts DC required for the majority of the MKB-I circuitry is
provided by a full-wave rectifier and a conventional series-pass regulator
circuit. A potentiometer permits adjustment of the output voltage over a
limited range.
The operational amplifiers, ICl and IC2, require a negative supply vottage
as we1I. A simple full-wave rectifier and filter circuit, followed by a
1N4735 zener diode regulator, supply the -6 volts required.
L2

5. CONSTRUCTION
The MKB-I consists of two main subassemblies, the 3 X 6 inch logic board
and the 5 X 11 inch keyswitch board, both of which mount in the keyboard
cabinet. The controls, connectors, and the power transformer mount directly
in the cabinet. Constructing the keyboard involves four steps:
1. Installing components on the logic board.
2. Installing the toroids and keyswitches on the keyswitch board
and wiring the toroid matrix,
3. Mounting components in the cabinet.
4. Connecting wiring harnesses between the subassembties and
the cabinet-mounted components.
Logic Board Construction
Referring to the parts list on page 37, sort out all the components marked
on the list with an rrl,rr. These are the parts that mount on the logic board.
Figure 5.1 shows the position of all parts on the board. Following the
numbered steps below, insert the parts into the board and solder the leads.
A11 soldering should be done on the bottom (non-component) side of the
board. Use just enough heat and solder to obtain good connections. Over-
heating may damage the board or the components. Check that excess solder
does not form a bridge between adjacent conductors.
I,Jhen installing vertically mounted components, position the component body
exactly as shown in the drawing to prevent interference with other parts.
Be sure to observe polarity when mounting components such as semiconductors
and electrolytic capacitors.
1. Mount all integrated circuits. Note thd U-shaped marking or dot
at one end of each IC, and install it so that this mark
corresponds to the position shornrn in the drawing. Solder
all leads carefully.
2. Insert all resistors and diodes. At each diode location one
of the pads is square. The cathode end of the diode should
be connected to the square pad. Solder all leads and trim
off excess length.
3. Insert all disc and mylar capacitors. Solder the leads and
trim off excess.
4. Mount and solder all transistors except the IdlE521.
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Insert the 500 ohm PC-mounting potentiometer in its location
near the right end of the board. solder the three leads.
Locate the MJE521 transistor and the black, U-shaped heatsink.
rf heatsink compound or non-conductive silicone grease is
avaitable, apply a srnalL amount to the gold plate on the side
of the transistor package. Lay the transistor on the heatsink
with the gold plate in contact with the heatsink. Insert the
transistor leads into the holes on the circuit board. Bend
the transistor and heatsink down toward the board so that the
hole in the transistor lines up with the mounting hole in the
circuit board. Insert a 4-40 X 3/A screw through the
transistor and heatsink, and fasten the pair to the board with
a locl<washer and hex nut. Solder the three leads.
7. Insert and solder the six electrolytic capacitorsr csrefulty
observing polarity. Trim off excess tead length.
The circuit board is nor^r complete. Check all connections carefully,
looking for leads which may not have been soldered. Then set the board
aside temporarily.
Kevswitch Board Construction
Referring again to the parts list, sort out those components designated
by a rrKrr. These are the parts needed to construct the keyswitch circuit
board. Figure 5.2 shows the location of the parts on the board. To
install them, fol1ow these steps:
rnsert the seven 1.2k, \ watt resistors in their positions
next to the mounting holes for toroids To through T6. Note
that these resistors are mounted vertically. The space
between the resistor body and its lead will be used later
to hotd toroid wiring in place.
9. The toroids are mounted at the seven holes near the edge of
the circuit board. Insert a piece of insulated stranded
hookup wire or strong twine (such as lacing or dial cord)
through hole AA at the left end of the row of toroid mounting
holes. Tie a knot in the end of the wire which protrudes
above the circuit board. From the bottom of the board, pull
the wire tight so that the knot rests on the top surface of
the board.
Holding the board with the top surface facing you, thread the
wire up through the mounting hole for toroid T6. pass the
wire through the center hole of one of the toroids, then
thread it down through the hole again. Position the toroid
so that it stands vertically on the board as shown in Figure
5,3 and pul1 the wire snug. Mount the remaining six toroids
in the same manner.
8.
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