Hal Communications DKB-2010 Instruction Manual Download

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Symptom: Keyboard produces incorrect characters or character codes

Suggested Tests:

Since the elements which determine the character codes are built into the encoder and ROM

integrated circuits at the time of manufacture, it is unlikely that they would cause transmission errors.
Much more probable is that one or more of the diodes in the memory matrix for the HERE IS sequencer

(Figure 8.13) or the three-letter sequencers (Figure 8.14) is reversed or shorted. These diodes will affect
the codes transmitted even when the sequencers are not active, since they are connected in parallel with

the ASCII output lines from the keyencoder.

It is often possible to determine which diode is at fault by comparing the ASCII code for the character

that should be transmitted with that for the character which actually is transmitted. The ASCII codes are

given in Table 4.2.

Symptom: HERE IS sequencer or three-letter sequencer produce incorrect codes

Suggested Tests:

A common problem which may cause the automatic sequencers to produce incorrect code patterns is

improper programming (diode placement) of the memory matrix. Refer to Section V for programming
instructions. An open-circuit diode or a missing diode will also cause transmission of an incorrect code for

one character.

Symptom: Keyboard sends all dots in Morse mode and all blanks in RTTY mode

Suggested Tests:

This failure mode indicates that the data buses carrying ASCII character codes from the keyswitch

circuit board to the logic circuit board are interrupted. An improperly installed edge connector is one

possible cause; a defective or incorrectly installed buffer memory option card is another.

Symptom: One or more keys fails to produce an output

Suggested Tests:

Check for a shorted or open keyswitch. The switches must be disconnected from the circuit before

they can be checked. Rather than removing the entire keyswitch module, it is more satisfactory to break
the conductor path to the non-grounded switch terminal with a scribe. Once the switch operation has

been checked with an ohmmeter, the path may be restored by laying a small piece of bare tinned wire
across the break and soldering it in place.

Test points for the Keyswitch circuit board and Power Supply circuit board are shown in Figures 6.2 and

6.3, respectively. Table 6.1, located on the same fold-out as Figure 6.1, gives the location on the logic circuit

board of the many different waveforms discussed in the text. Integrated circuit designator numbers are
printed on the circuit board. Pin 1 of each IC is indicated by a "flag".

Tables 6.2 and 6.3 show the signals or voltages present at the three edge connectors. A complete wiring

list for the wire harness is presented in Table 6.4. Wire colors are assigned only for those wires that connect
to panel mounted components. Wires that only connect between circuit board edge connectors are not
assigned specific colors and are generally the same color in a given harness.

The IC pin numbers for ground and power connections are shown in Table 6.5.