Heathkit HD-1410
The Heathkit HD-1410 Features
Self-completing Dots and Dashes
Dot and Dash Memories
Iambic Operation
Dot and Dash Insertion
Built-in Paddles
5-50 WPM Speed Range
Built-In Sidetone Oscillator and Speaker
Headphone Jack that silences the Speaker
Solid-state Output.

As I mentioned in the introduction to this section, the Heathkit HD-1410 was the first keyer that I ever owned. Since it was also my only keyer, I really didn't have anything to compare it to. So I thought it was great. Some hams didn't like the built-in Paddles. They complained that it was hard to get the same response from both paddles. Personally, I found the paddles very easy to work with and easy to set up. All you need is a little patience.

While the HD-1410 is capable of Iambic Operation, I never bothered to use that feature. I researched it a bit, and tried operating the keyer Iambicly, but found that all I did was create a bunch of errors.

Note that, some of the descriptions below are similar to versions of the explanation provided by Heathkit in their manual.

Also note that, in my schematics, integrated circuits that contain multiple logic elements, like the SN7400 which contains four 2-Input NAND gates, may not have the same element designator as the original original schematic. Where necessary, this had been adjusted for in the explanations. However, the integrated circuit pin numbers do match the original schematic.

Further, for Reference Designators, Heathkit used "IC". Whereas, I use "U".

The schematic for the Heathkit HD-1410 keyer is below. Due to available space, and the fact that I don't like cluttered schematics, I split the schematic into four drawings. I tried to include everything that the original schematic had, but then the drawings start to get cramped and cluttered. The Block Diagram, below, shows how the schematic was divided up.

Heathkit® HD1410 Iambic Keyer - Block Diagram
DOT
DASH
DASH
RESET
U5C,U2D
DASH NEXT
BIT MEMORY
U1B,U2B
PRESENT BIT
MEMORY
U3A,U3B
DOT NEXT
BIT MEMORY
U1A,U2A
DOT RESET
U5D,U2C
CLOCK
ENABLE
U1C,U1D
CLOCK
Q1,Q2
SPEED
BIT
GENERATOR
U4A,U4B,U3C
HOLD
SIDE TONE
OSCILLATOR
U5A,U5B,Q3
TONE
OUTPUT
CIRCUITRY
Q4,Q5,Q6,Q7
Keyer Out
RX Audio
POWER
SUPPLY
Q8
OFF
EXT 12V
120/240 VAC
+5 V
To all IC's
and Transistors
V
O
L
U
M
E
+5V
Phones
+
-
+5V
DOT/DASH DETERMINATION
Schematic
Page 1
Schematic
Page 2
Schematic
Page 3
Schematic
Page 4
Page 1 - Next-Bit Memories" (NBM), Present-Bit Memories (PBM), and Reset Circuitry

There are two "Next-Bit Memories". One for Dots, composed of U1A and U2A. And one for Dashes, composed of gates U1B and U2B. Each pair of gates is cross-coupled to form an S-R (Set-Reset) flip-flop. Since their operation is similar, only the Dash NBM will be discussed.

When no bit is being sent, U2D‑8 is a 1, since the clock (CLK_Q2) is a 1. The Dash NBM is in the reset condition, with U2B‑6 at a 1 and U1B‑3 at a 0. This 0 is applied to U3B‑4. Therefore, U3B‑6 is a 1. (Similarly, U3A‑8 is also a 1.) When the Dash paddle is keyed, U1B‑2 is grounded momentarily through the paddles contacts. This causes U1B‑3 to go a 1. U2B‑4 and 5 are both at a 1, so U2B‑6 goes to a 0. This 0 is applied to U1B‑1 and holds U1B‑3 at a 1 after the paddle is released. U3B now has a 1 on all three inputs, so pin 6 is a 0. This 0 is applied to U1C‑13, and U1C‑11 goes to a 1. U1D‑8 goes to a 0, and the bit generator begins to form a Dash (since U4B‑2 is at a 1).

Note that U3B and U3A form a S-R flip-flop which, depending on its state, causes the Bit Generator to form Dots or Dashes as described in the section on bit generation.

At the end of a bit, whether Dot of Dash, the PBM must assume the state of the next bit to be sent. This is accomplished by the Reset Circuitry. U5C, U2B, resistor R3, and capacitor C1 form the Dash Reset circuit. (The Dot Reset circuitry is composed of U5D, U2A, resistor R4, and capacitor C2 operates the same.) Iambic operation requires that if both paddles are closed, or if the Dot paddle is keyed during a Dash bit, or the Dash paddle is keyed during a Dot bit, the next bit must be opposite to that being sent.

Assume a Dot is being sent. This means that U3A‑8 is 0 and U3B‑6 is 1. This 1 is applied to U5C‑9 and holds U5C‑10 at a 0. The trailing edge of the clock pulse occurring a the end of the Dot bit mark takes U3C‑12 at a 0. At this time, U5D has both inputs at a 0, and U5D‑13 goes to a 1. This enables U2C for the next clock pulse, which occurs at the end of the Dot bit. The leading edge of this clock pulse takes U2C‑11 to a 0. This will reset the Dot NBM unless the Dot paddle is still closed. If the Dash paddle has not been closed, then there is a 0 on U3B‑4 which holds U3B‑6 at a 1, and the PBM cannot change state. Thus the next bit will be another Dot. If, however the Dash paddle had been keyed sometime during the Dot bit, then U3B‑4 will be high. When U2C‑11 goes to a 0, U3A‑10 goes to a 0, and U3A‑8 goes 1. Then U3B has all inputs at a 1 so U3‑6 goes to a 0 and holds U3‑8 at a 1 following the clock pulse. On the trailing edge of this clock pulse, the Bit Generator begins a Dash, since U4‑2 is a 1.

A necessary delay is provided by R3 and C1. Recall that when the PBM changed state, U3‑6 went low on the leading edge of the clock pulse. U3‑12 does not go to a 1 until the trailing edge of the clock pulse. Were it not for the delay, U2‑9 and 10 would be at a 1, and the 0 on U2‑8 would remove the Dash from this memory if one were stored there.

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1
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1
A
B
C
D
A
B
C
D
Heathkit®
Title
Bit Memories/Reset, Clock Enable
Size
B
Document Number
Model HD-1410 Keyer
Rev
None
Date:
3/7/2020
Sheet 1 of 4
Dot
Dash
Heathkit
K1
SHOWN WIRED
FOR RIGHT HAND
OPERATION
B
A
R1
2,200Ω
+5V
R2
2,200Ω
+5V
10
9
8
SN7400
U2
D
CLK_Q2
P2-D5
4
5
6
SN7400
U2
B
1
1
1
2
3
SN7400
U1
B
1
0
4
5
6
SN7400
U1
A
1
0
1
2
3
SN7400
U2
A
1
1
13
12
11
SN7400
U2
C
CLK_Q2
P2-D5
5
4
3
6
SN7410
U3
B
11
9
10
8
SN7410
U3
A
DASH_CLR
P2-A4
13
12
11
SN7400
U1
C
0
10
9
8
SN7400
U1
D
3.1
CLK_ENA
P2-B8
8
9
10
SN7402
U5
C
CW_OUT
P2-B1
R3
390Ω
+
C1
22µF
8.6 mS
11
12
13
SN7402
U5
D
CW_OUT
P2-B1
R4
390Ω
+
C2
22µF
8.6 mS
Present Bit
Memory
Dash Next
Bit
Dot Next
Bit
Dash Reset
Dot Reset
Page 2 - Clock and Bit Generator
Heathkit®
DOTS
DASHES
Figure 10
IC4 PIN 5
IC4 PINS
1 AND 8
IC3 PIN 2
IC4 PIN 13
IC3 PIN 1
IC3 PIN 12
DOT PADDLE CLOSED
DASH PADDLE CLOSED

The clock consists of transistors Q1, Q2, and their associated circuitry. When CLK_ENA is high, the clock (CLK_Q2) is disabled. Capacitor C3 charges through diode D1 and biases Q1 off. With Q1 off, the base of Q2 is high. Therefore, Q2 is also off and the clock output is low. Note that the high on CLK_ENA is also applied through D2 to U4A pin 5. When CLK_ENA goes low (bit being sent), U4A changes state. D1 is then back-biased and C3 begins to discharge through resistor R9, Speed control R101, and resistor R11. When its voltage drops to the base potential of Q1, Q1 begins to turn on. The collector of Q1 and the base of Q2 begin to go less positive and turn on Q2. As Q2 turns on, its rising collector potential is coupled through capacitor C4 to the base of Q1 and turns it on harder. Thus the condition is regenerative and happens very quickly.

The Bit Generator is composed of U4A and U4B, and U3C. In the resting condition, U4A and U4B are reset (Q outputs are 0). The 1 on U3C‑1, 2, and 13 causes U3C‑12 to be a 0 (Key-Up). If U4B‑2 is a 0, U4B cannot change state. The waveform in Figure 10 show how Dots and Dashes are formed. Note that if U4B‑2 is 0, Dots are generated; if it is a 1, Dashes are generated.

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C
D
Heathkit®
Title
Clock and Bit Generator
Size
B
Document Number
Model HD-1410 Keyer
Rev
None
Date:
3/7/2020
Sheet 2 of 4
Q1
MPSA20
+
C3
2.2µF
Q2
X29A829
R5
100KΩ
+5V
R6
39KΩ
+5V
R7
22Ω
+5V
R8
15KΩ
C4
0.001µF
R9
**
SPEED
50KΩ
R101
R11
100Ω
CLK_Q2
P1-B3, P1-D3
D1
GD-510
CLK_ENA
P1-C2
D2
GD-510
D3
GD-510
2.7
R12
270Ω
R
J
K
Q
Q
5
7
10
6
9
8
SN7473
U4-A
R13
1000Ω
+5V
R14
4,700Ω
R15
4,700Ω
R
J
K
Q
Q
1
14
3
2
12
13
SN7473
U4-B
DASH_CLR
P1-B4
13
2
1
12
SN7410
U3
C
CW_OUT
P3-B8
R16
2,200Ω
+
5
V
EXT KEY
J101
HOLD
S101
E
F
** R9 = 5.6KΩ - Range is 10 to 60 WPM
     R9 = 10KΩ - Range is 10 to 35 WPM
     R9 = 5.6KΩ and Shunt R101 with 33KΩ - Range is 8 to 35 WPM
Page 3 - Side Tone Oscillator, Transmitter Keying Circuit

The Sidetone Oscillator is made up of U5A and B, which are cross-coupled to form an astable multivirator. It is enabled when U5B Pin 6 goes to a 0. Its output is coupled to Q3, which drives the speaker.

When U3C‑12 (Page 2) goes to a 1 (mark condition), it turns on the Darlington pair, transistors Q6 and Q7, which will key positive lines to ground. Transistor Q4 also turns on, thus turning on transistor Q5 and keying negative lines to ground through the power supply and resistor R25. Note that no more than approximately 10 mA may be keyed by this circuit since it is a constant sink which limits at 10 mA. Diodes D4 and D5 isolate the two sections.

The Keyer Output line is bipolar and can handle positive keyed lines (Cathode Keying) as well as negative keyed lines (Grid-Block Keying) that are common with vacuum tube transmitters. This seems to work nicely, but it has been suggested that three of the output transistors could be replaced with more modern devices with better ratings.

  • Q5 could be replaced with a with an NTE288 transistor (PNP - 300 Volt, 500 mA, 625 mWatt)
  • Q6 and Q7 with a pair of NTE287 transistors (NPN - 300 Volt, 500 mA, 625 mWatt)

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C
D
Heathkit®
Title
Side Tone, TX Keying
Size
B
Document Number
Model HD-1410 Keyer
Rev
None
Date:
3/7/2020
Sheet 3 of 4
2
3
1
SN7402
U5
A
5
6
4
SN7402
U5
B
R18
150Ω
+
C5
2µF
+
C6
2µF
R19
150Ω
R17
750Ω
TONE
C7
0.2µF
R27
8,200Ω
R23
4,700Ω
CW_OUT
P2-B1
R22
4,700Ω
Q3
MPSA20
+5V
G
H
R102
100
V
O
L
C101
0.2µF
SP1
45Ω
+
-
J102
Headphones
J103
RCV IN
Q4
MPSA20
R24
4,700Ω
+5V
R25
4,700Ω
+5V
Q5
MPS-D51
R26
4,700Ω
Q6
MPSA42
R27
1,000Ω
Q7
MPSA42
D4
1N2071
D5
1N2071
J
C103
0.005µF
J104
KEYER
OUT
Side Tone Oscillator
Keyer Output Circuit
Cathode Keying
Grid-Block Keying
Page 4 - Power Supply and Power Wiring

The Power Supply is conventional series regulated bridge circuit that supplies +5 volts. Diode D6 protects the power supply against reversed battery polarity.

The supply can be configured to operate from 240 Volts AC, 120 Volts AC, or 12 Volts DC. On 120 Volts AC, the two primaries are run in Parallel. On 240 Volts AC, the two primaries are run in Series. The appropriate fuse should be used based on the supply voltage. The power and ground wiring is included for the ICs on page 1, 2 and 3

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C
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A
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C
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Heathkit®
Title
Power Supply
Size
B
Document Number
Model HD-1410 Keyer
Rev
None
Date:
3/7/2020
Sheet 4 of 4
1
2
3
S101
432-148
1
2
3
P101
432-149
EXT 12V
SOURCE
-
+
CHASSIS
CONNECTOR
120VAC
LINE
CORD
F1
1/16 A SB
C104
0.001 µF
1,400V
C102
0.001 µF
1,400V
T1
120 VAC : 10.0 VAC
1
3
2
4
5
6
120 VAC WIRING
USE 1/16 A FUSE
K
D6
1N4002
L
M
T1
240 VAC : 10.0 VAC
1
3
2
4
5
6
L
M
240 VAC WIRING
USE 1/32 A FUSE
R103
33KΩ
PL1
412-15
S1A
R102
S1B
R102
PART OF
R102 (VOL)
D8
1N4002
D9
1N4002
D11
1N4002
D12
1N4002
+
C11
1,000µF
R28
220Ω
D7
1N709A
Q8
417-212
C
E
B
12.2V
5.0V
6.3V
C8
0.1µF
C9
0.1µF
+5V
+5V
SOURCE
VCC
GND
14
7
U1 - SN7400
+5V
VCC
GND
14
7
U2 - SN7400
VCC
GND
14
7
U3 - SN7410
VCC
GND
4
11
U4 - SN7473
VCC
GND
14
7
U5 - SN7402
+5V
Schematic Notes
1.Component numbers are in the following groups.
1-99 parts mounted on the circuit board
101-199 Parts mounted on the chassis.
2.All Resistors are 1/4 watt unless marked otherwise.
Resistor values are in Ohms (K=1000).
3.Voltages may vary +/-20%,
4.All capacitor values are in MicroFarads (µF)
5.Refer to the chassis photographs and circuit board
X-Ray views for the physical location of parts.
6.
This symbol indicates circuit board ground.
7.
This symbol indicates chassis ground.
8.
G
This symbol indicates a lettered circuit board
connection that is soldered.
9.
This symbol indicates a part not mounted on the
circuit board.
10.→  Indicates clockwise rotation of control shaft.
11.
RF
RF
This symbol indicates that like points are connected together.
12.
This symbol indicates a DC voltage taken under the following conditions from the point indicated to chassis ground with a high impedance voltmeter.
  1. Keyer disconnected from transmitter.
  2. Keyer connected to AC power.
  3. All controls set to midrange.
  4. Speed knob pushed in.
13.L - Low level logic. Approx. 0.09V
14.H - High level logic. Approx. 4.0V
15.* This symbol indicates the voltage depends on
the settings of control R17
16.The waveforms were taken under the following conditions:
  1. Speed knob pulled out (Hold), tone control in mid position.
  2. Both paddles depressed.
  3. Speed control at 12 o'clock position, Dash paddle depressed.
  4. Speed control at 12 o'clock position, Dot paddle depressed.
17.**R9 = 5600Ω for 10 to 60 words per minute speed.
R9 = 10KΩ for 10 to 35 words per minute speed.
Keyer Timing

The image below is redrawn from the Verilog simulation of the HD-1410 keyer. I redrew it because it allows me to annotate easier. The times, "T0 to T20", are arbitrary times and are applicable at any speed. They are only used as event markers.

The image shows the basic operation of the HD-1410 logic sending the letters "A", and "B". The keyer controls the length of the dots, dashes, and space between letter elements. However, space between letters and words is up to the keyer operator.

In the simulation, the top two traces are the Dot and Dash Paddle input. The paddle inputs are normally "high" and are taken "low" when a paddle is closed. The arrows from the first dot (T1) show that the dot paddle closure sets the "Dot_Set" register, which then sets the "Clk_Ena". A short time after the dot paddle is closed, and released, the dash paddle is closed (T2 ≬ T3). As long as the dash paddle is closed before the space following the dot is complete, a dash will be produced and the "Clk_Ena" will continue to be active. The dash is self completing so the dash paddle can be released before the dash is completed.

Below the paddle inputs is the CW_Out signal. This signal happens before the Keyer Output Circuit on Page 2. When the CW_Out signal is "high" the transmitter is being keyed.

Heathkit®
T0
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
T13
T14
T15
T16
T17
T18
T19
T20
Dot_Paddle
Dash_Paddle
CW_Out
Keyer_Clock
Clk_Ena
Dot_Set
Dash_Set

The waveforms shown here, only deal with one method of sending. I also simulated "squeeze" keying and verified that an extra dot can be generated, if the paddles are not operated properly. There is no fix for the extra dot, but there doesn't really need to be one. Many of the other keyers included in this section, have the same issue.

HD-1410 Modifications

Keyer Speed

On page 2 of the schematic, is the Keyer Clock. The keyer speed, in WPM (Words Per Minute), is controlled by R9. If you use 5,600Ω for R9, the speed range should be from 10 to 60 WPM speed. But it may be difficult to adjust the speed, due to the wide range. To reduce the WPM range to 10 to 35 WPM, R9 can be changed to a 10KΩ resistor.

That suggestion works fine but another suggestion is to add a 5.6KΩ resistor in series with R9 and then shunt Speed Control, R101, with a 33KΩ resistor. That should change the speed range to 8 to 35 WPM.


Modifications For Use With Ten-Tec, Triton And Rigs With Similar Keying

Heathkit®
Q4
MPSA20
U5B-6
R23
4,700Ω
CW
OUT
R24
4,700Ω
+5V
R25
4,700Ω
+5V
Q5
MPS-D51
R26
4,700Ω
Q6
MPSA42
R27
Q7
MPSA42
D4
1N2071
D5
J
C103
0.005µF
J104
KEYER
OUT
Keyer Output Circuit
Cathode Keying
Grid-Block Keying
From Keyer
Logic - P1

These modification are described in the Service Bulletins listed below. But I thought a schematic of the modification would be nice.

Bulletin No: HD-1410-1, Part A - If you match this drawing up with the Keyer Output Circuit, on page 2, you should notice that R27 and D5 are replaced with resistors (or wire jumpers). Using a resistor in R27 shorts the base of Q7 to ground, effectively, removing Q7 from the circuit. Using a resistor in D5 eliminates the 0.7 VDC offset from ground.

Bulletin No: HD-1410-1, Part B - If the keyer needs to be used with Cathode OR Grid-Block keyed rigs, the modifications in the drawing should be made, and used for Grid-Block keyed transmitters "only". For rigs that employ a positive key line, and solid state keying circuits (Cathode keying), the "Ext. Key" jack is repurposed.

The modification consists of mounting a terminal strip (three terminals with center terminal ground) below the "Ext. Key" jack. Mount a 4,700Ω resistor across pins 1 and 3. Then mount a MPSA20 transistor on the terminal strip with:

  • Base - Connected to lug 1
  • Emitter - Connected to lug 2 (center)
  • Collector - Connected to lug 3
. Then, the Base of the transistor is wired to the Lug 3 of Terminal Strip to junction of R23 and R26 on circuit board./p>
Service Bulletins
April 17, 1975
HD-1410 Electronic Keyer Bulletin No: HD-1410-1
Modifications For Use With Ten-Tec, Triton And Rigs With Similar Keying Requirements
It has been found that the Ten-Tec Argonaut and Triton keyin circuits require that the key-line be brought to within a few tenths of a volt of ground to operate properly, Either of the following modifications to the HD-1410 will allow it to be used with the above units:
  1. If the HD-1410 is to be used exclusively with the Ten-Tec or rigs with similar requirements, R27 and D5 can be replaced with jumper wires. This disables Q7 and eliminates the .7 volt drop due to D5.

  2. If the HD-1410 is to be used both with such rigs and cathode or grid block keyed rigs, the modification shown on the attached schematic may be made. The jack labelled "Ext. Key" becomes a secondary "keyer-out" jack for use only with rigs employing a positive key line, and solid state keying circuit.

  1. Refer to page 40 of assembly manual and remove the wire between jack L, lug 1 [Keyout Jack] and circuit board hole F.

  2. Disconnect the remaining wire from jack L, lug 1 and connect to circuit board hole F.

  3. Mount terminal strip and components as shown:
    [[ Shows TS 431-62 To be mounted under top screw of Jack L and bent down slightly. Connect a 4700 Ohm resistor between lugs 1 and 3 of TS 431-62. Connect base of [PN 417-801] to lug 1 of TS 431-62; emitter to one lug of Jack L and the collector to the other Jack L lug ]]

  4. Connect wire from Lug 3 of Terminal Strip to junction of R23 and R26 on circuit board. Solder this wire to lead of R26.

Keyer Keys Continuously Or Erratically
Problems with RF causing the keyer to key continuously or erratically, particularly when using long wire or random length antenna systems, can be eliminated by connecting a .001 µF disc ceramic across the keyer output jack.
Intermittent Sidetone
In some units, if the "tone" control is turned fully clockwise [low frequency end], the sidetone will be intermittent. Turning the pot slightly counterclockwise will eliminate the condition.
May 20, 1975
HD-1410 Electronic Keyer Bulletin No: HD-1410-2
Service Guide
The following is a step by step procedure for servicing the HD-1410 Keyer:
Equipment Needed:
1 VTVM [Not a VOM or DVM]
Set VTVM as follows:
To read DC + Voltage
Set controls on HD-1410 as follows:
AC Switch - ON
Speed - Full CCW
Volume - 1/4 CW

C A U T I O N

When making voltage checks in the unit, be very careful where the probe is touched as 110V AC voltage is present also.

  1. The first test is to check the DC voltages for the power supply and pass transistor Q8. If any deficiencies are found in this area, they must be corrected before proceeding on.

  2. The most important section in the keyer is the Dot Generator and Dash Divider, this will be checked as follows:

    With the keyer shut off, connect a jumper wire from pin 8 of IC1D to ground. With the keyer set up in this manner, both the dot generator and dash divider can be checked at the same time without pushing the paddles. Turn the keyer on. Connect the ground lead of the VTVM to the chassis of the keyer.

    1. Set the VTVM to a 1.5VDC range and touch the probe to pin 10 of IC2D. The meter should read about .16 and the needle should be oscillating slightly. If these results are not obtained, check Q1, Q2, C3, D1 and speed control.

    2. Set the VTVM read +5VDC range and touch meter probe to pin 5 of IC4A. Reading shuld be .16VDC with needle oscillating slightly. Check D3 and R12, if proper results are not obtained.

    3. Touch meter probe to pin 8 of IC4A. Meter needle should oscillate rapidly between 1.5 and 2.5VDC. If proper results are not obtained, first check pin 2 of IC4A. Meter needle should oscillate between 3.6 to 4VDC at half the rate of pin 8. Replace IC-4, if necessary.

    4. Touch meter probe to pin13 of IC4B. Meter needle should oscillate between .5 and 3.5VDC at 1/2 the rate of test C above. If proper results are not obtained, check pins 14 and 3 of IC-4 for 5VDC. Replace IC-4, if necessary.

    5. Touch the meter probe to pin 12 of IC3C. Meter needle should oscillate from 1.6 TO 3.4VDC. If proper results are not obtained, check pin 13 of IC3C for 5VDC. Replace IC3C, if necessary.

  3. Output circuitry: Since the jumper is already installed in the bit generator and dashes are being produced, we'll use this same approach for checking the output circuitry.

    1. Touch the meter probe to the [C] of Q4. Meter needle should swing between .2VDC and 2.8VDC. If proper results are not obtained, check resistor R24.Replace Q4.

    2. Touch the meter probe to the [C] of Q5. Meter needle should oscillate between .3VDC and .8VDC. If proper results are not obtained, check R25. Replace Q5.

    3. Touch meter probe to point [J] or keyer output jack. Meter needle should oscillate from .3VDC to .8VDC. If proper results are not obtained, check or replace D4.

    4. Repeat the same procedure for Q6, Q7 and D5.

  4. Tone oscillator circuit. Jumper will still be connected to pin 8 of IC1D.

    1. Touch meter probe to pin 4 of IC5D. Needle should oscillate between .6 and 1.4VDC. If proper results are not obtained, check C5, C6, tone control. Replace IC-5.

    2. Touch meter probe to [C] of Q3. Meter needle should oscillate between 4.3 and 4.7VDC. If proper results are not obtained, check C7, R21. Replace Q3.

  5. Paddle control and memory logic: Shut off the keyer and unsolder the jumper wire from pin 8 of IC1D.

    1. Turn the keyer on and with the VTVM check the logic levels for IC-1, IC-2 and IC-3 as shown on the schematic. With both paddles released the logic levels will be reversed.

    2. Memory bit problems can only be in IC-5, R3, R4, C1 and C2.

May 20, 1975
HD-1410 Electronic Keyer Bulletin No: HD-1410-3
Keyer Keys Continuously Or Erratically
In the next run, a .005MFD [5000pF, PN 21-57] will be added across the Keyer output jack.

This supersedes the information in Bulletin No: HD-1410-1
26, 1976
HD-1410 Electronic Keyer Bulletin No: HD-1410-4
No Dots Or Dashes
If the unit has no dots or dashes output, but has a tone in the "hold" mode, check the installation of Q2. The customer apparenly tries to twist the transistor so that the flat of the transistor will align with the flat screened on the board. This will cause the base & collector leads to short.

The manual is being changed to clarify the installation of this transistor.
JUNE 24, 1976
HD-1410 Electronic Keyer Bulletin No: HD-1410-5
RFI
RFI in the keyer coming through the power supply can be eliminated by installing two .005UFD/1.6KV capacitors [PN 21-44] across the AC line to the ground.
July 9, 1976
HD-1410 Electronic Keyer Bulletin No: HD-1410-6
Wrong Type Of Round Knob
Some kits were shipped with round knobs [PN 462-932] that will not accept the knob bushing. Although these knobs will fit onto the control shafts, the knob pointer may not align properly.
September 23, 1977
HD-1410 Electronic Keyer Bulletin No: HD-1410-7
Keyer Locks On Some Bands
++++Info not yet available++++
September 23, 1977
HD-1410 Electronic Keyer Bulletin No: HD-1410-7
Keyer Locks On Some Bands
++++Info not yet available++++
July 24, 1978
HD-1410 Electronic Keyer Bulletin No: HD-1410-8
No Dashes; Tone And Dots Okay
Check for a possible foil bridge between pins 8 and 9 or between pin 8 and ground of the Dash Reset circuit, IC2 [PN 443-1]. The bridge is usually too small to see without a magnifier. The bridge usually can be removed by scraping the area around pins 8 and 9 with a knife or other similar object.
May 8, 1980
HD-1410 Electronic Keyer Bulletin No: HD-1410-9
Sidetone Not Loud Enough
++++Info not yet available++++