MFJ-482B Grandmaster Memory Keyer

This particular keyer took a lot of work. Mostly because the schematic from the manual is probably the worst schematic that I have ever seen. But maybe that was the intent by MFJ. Users always want a schematic of the device. Not that they will try to build one. They just want it. So if you provide them with a undecipherable schematic, the user is happy.

But I wanted something that is a bit more readable. So I split the schematic into multiple pages. I still don't think anyone is going to home brew one, but it may be more understandable.

Page 1 - Keyer Section

This page contains the Keyer section of the MFJ-482. The logic that handles the Dot/Dash Next Bit memories, the Dot/Dash Reset, and the Present Bit Memory, are pretty straight forward. A similar arrangement is used on many other keyers. But Bit Generator puzzled me for a while. It wasn't until I realized that the "Q" output of both flip-flops are expected to be a "1", in a initial and idle state.

Page 2 - Clock Section

This is a fairly critical section of the keyer.

Page 3 - Sidetone, CW Weight, and Keying Output Section

This page contains the Sidetone Oscillator, CW Weighting, and the Keying Output.

MFJ-482B Grandmaster Memory Keyer Manual

The MFJ-482B Grandmaster Memory Keyer is a sophisticated memory keyer using CMOS Integrated Circuits and Random Access Memory. It has 1024 bits of memory space that will store approximately 100 characters (four 25 character or two 25 and one 50 character message). To insure full benefit of this memory keyer. Please read this instruction manual before operating.

Control Functions

  1. SPEED CONTROL (P2-R9). Speed is variable from 8 to 50 WPM.
  2. WEIGHT CONTROL (P1-R8). This control is located on the rear panel. When turned fully counter clockwise, dot-dash-space ration is perfect 1:3:1. Turn this control clockwise to increase dot dash lengths.
  3. TONE CONTROL (P2-R13). THis control is located on the rear panel. Use it to adjust for desired sidetone pitch.
  4. VOLUME CONTROL (P2-R16). Use to adjust the loudness of the built-in sidetone.
  5. RECORD, SEND, REPEAT, TUNE FUNCTION SWITCH (P?-S??). The RECORD position sets the memory keyer in the record mode for recording messages into memory. The SEND position allows playing back recorded messages and allows the memory keyer to be used as an electronic keyer. The REPEAT position allows repeating the recorded message continuously. The TUNE position keys your transmitter continuously for tuning
  6. COMBINE A/B SWITCH. Push this switch in to combine A and B memory addresses.
  7. ON/OFF SWITCH (P4-S2). Push this switch in to turn on the memory keyer. All messages stored in the memory are erased when this switch is let out. Keep power on to maintain memory.
  8. RESET BUTTON. It is used to stop memory from operating. When sending a recorded message, memory can be stopped by pressing the reset button or by tapping the keyer paddle. This resets all memory addresses to the begining.
  9. LED INDICATOR. Shows when memory is in operation.
  10. MEMORY ADDRESS (P4-S1, S2, S3, S4). Four push buttons A, B, C, D are used to directly address the memory. Press a MEMORY ADDRESS button to start a message. Memory operation can be interrupted by pressing another MEMORY ADDRESS button without pressing the RESET button first.
  11. MEMORY SAVER. An internal 9 volt battery (not provided, alkaline type recommended) switches in automatically when a power failure occurs. This allows all messages to be retained. A battery clip and holder are provided for installation of a 9 volt alkaline battery. If the side tone is not used, the memory backup battery has an operational time, of approximately eight hours. If longer storage time is needed an external battery of 12-15 VDC may be connected to the battery jack on the memory keyer. NOTE: MEMORY SAVER is also turned off when the ON/OFF switch is turned off.

Installation

  1. To install the memory saver battery, remove the two screws near the rear top. Slide the cover toward the back and remove. Connect a 9 volt battery to the battery snap then insert the battery into the holder. A 9 volt alkaline battery should be used. When the memory saver batter is not used, cover the battery snap with the plastic tubing supplied to prevent shorting.
  2. The MFJ-482B requires a 12-15VDC for operation. A 2.5mm sub miniature plug is needed. Wire the plug so that the tip is positive and the sleeve is ground. AC adapter (MFJ-1313) is optional. First plug the adapter into the sub miniature jack on the rear panel, marked "adapter", and then plug the adapter into the 110 VAC wall socket. It is not necessary to unplug the AC adapter when the memory key is not in use.
  3. During portable use, when 110 VAC is not available, plug external batteries into the 12-15 VDC sub miniature jack on the rear panel. External batteries and the memory saver can never come into use unless power from the adapter is lost. The tip of the sub miniature plug is positive and the sleeve is ground, for the AC adapter and external batteries.
  4. A squeeze or single lever key can be used. Squeeze keys allow IAMBIC operation. Use a standard quarter inch stereo plug and a two conductor shielded cable of two separately shielded cables. Tie the shields together and use it for ground. The dot wire should be connected to the ring of the plug, the dash wire to the tip and the shield to ground.
  5. A reliable solid state keying circuit allows keying of a grid block, cathode, and solid state transmitter. For grid block keying use the "Grid Block" keying output, For cathode keyed and solid state transmitter, use the "Direct" keying output. Try both outputs if you are uncertain of which output to use. The keyer outputs are self protected. The "Grid Block" output keys a maximum negative voltage of 300 volts to ground at 10ma. The "Direct" output keys a maximum positive voltage of 300 volts to ground at a maximum current of 100ma. Use a shielded cable to connect bwtween the memory keyer and the transmitter key input.

Operation Procedure

  1. Apply power to the memory keyer.
  2. Plug in key paddle to the KEY jack. A dual paddle squeeze key or a single lever key can be used.
  3. Turn Function Switch to SEND position.
  4. Start sending with the paddle and adjust the volume, tone, weight, and speed. The TONE and WEIGHT are located in the back panel. NOTE: The weight control may cause a stedy tone at high speed. Should this occur, the weight or the speed must be reduced by turning the controlls counter clockwise until it stops.
  5. The dot and dash memories ease sending by allowing keying the dot before the completion of the dash or vice versa. This feature can checked by setting to the lowest speed and tap first the dash lever then the dot lever before the dash and the dot. The keyer will provide both the dash and the dot. The dash memory can be checked by first tapping the dot then the dash. The dot insertion features allow you to tap the dot side to insert a dash while holding the dot side in. When using squeeze key and with both paddles squeezed together the IAMBIC operation features alllows sending of alternate dots and dashes. The first contact determines whether a dot or dash occurs first.

Memory Operation

  1. RECORDING
    1. Turn the Selector Switch to the RECORD position.
    2. Adjust SPEED control for desired speed. Press a MEMORY ADDRESS button (A, B, C, or D) and start sending immediately. (NOTE: Recording will not start until a MEMORY ADDRESS button is pressed while in the record mode.) Memory LED will light up when memory is in operation. Message including spaces is being recordes as long as the LED is lit in the record mode. When LED goes out, this indicates the memory is full. If the LED goes out before sending is completed, the message is too long. Combine memory address A and B by pushing in the COMBINE A/B switch to double the memory space. When recording, the internal clock runs continuously to allow spaces of any length to be entered into the memory; thus, there is a random delay from zero to the length of one dot. This requires you to synchronize your sending with the keyer to some extent. At low speed (10-15 WPM) dots may eve be missed occasionally. This can be avoided by not releasing the dot lever until a dot starts.
    3. Occasionally, an unwanted dot may appear in the beginning of a recorded message; this is due to improper erasing. To insure a complete erasure of previously recorded message in the memory when recording it is best to press the address button two or three times before sending. Note that the MEMORY ADDRESS, when pressed, resets the memory to the beginning of that address either record or play mode; beginning of that address either record or play mode is therefor, the reset button need not be pressed when programming. A recorded message can also be corrected by first playing the correct part of the messand and just before the mistake turns the record mode to complete recording the message. NOTE: The memory keyer will key the transmitter in the record mode. It must be disconnected from the transmitter during recording. The transmitter may also be disabled by switching the transmit/receive switch to the receive mode.
  2. PLAY BACK
    1. Turn the Function Switch to SEND. This puts the memory keyer in the play mode. Press the desired MEMORY ADDRESS button.
    2. The LED indicates memory is in opertion. MEMORY ADDRESS resets message to the beginning once it is pressed.
    3. To interrupt a playing message, or to make an insertion, simply send at the point where changes are to be made. The message can be continued by pressing another MEMORY ADDRESS button which contains the remainder of the message.
    4. To repeat, turn the function switch to the REPEAT position then press the same MEMORY ADDRESS button. The recorded message will repeat continuously until it is interrupted. NOTE: The repeat function will repeat both messages and any length of space at the end of a message. Recording a pause a the end of a message will allow you to listen before the message is repeated again.