Vectronics VEC-221K - Manual (Page 31)

VEC-221K Instruction Manual CW Memory Keyer Kit
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mistakes. What is needed is a “fresh” set of eyes. Enlist a friend to go over your
work.
Always check the obvious! Is the battery dead or weak? Is the power switch on?
Check the keying cable and paddle cable for intermittent or broken wires. Note
that the solder connections for the various jacks may fail due to stress from
frequent insertion and removal of plugs.
Trouble shooting guide:
Performing the self-test will isolate the problems in most cases.
No sidetone, but keying line actuates: Use a scope to view the sidetone signal
from pin 13 of U1. Look for the sidetone signal at R2, R3, R4, C13, pin 3 of
U3, pin 5 of U3, and both sides of C18 to isolate problem stage. Set scope for
AC coupling, 100 mV (or higher, as needed) per-division. Pin 6 of U3 should
show 9 Vdc. Pin 5 of U3 should measure about 4.5 Vdc with no tone (use scope
or VOM).
Dot or Dash characters not being generated: Dot lever should produce low-
going logic level at pin 28 of U1. Dash level should produce low-going logic
level at pin 27 of U1. Check pin 12 of U1 for high-going CW signal. Check for
5 Vdc on pins 1 and 20 of U1. Set scope for DC coupling, 1 volt-per-division.
Sidetone okay, but keyline remains low: Check for high-going logic signal
from pin 12 of U1 when paddles are actuated. Set scope for DC coupling, 1
volt-per-division. Presence of signal indicates possible failure of Q1 or D1.
Keyer dead: Check for 9 volts at pin 6 of U3. Check for 5 volts at pin 20 of
U1. Loss of 5 volts may indicate failure of U4 voltage regulator.
Sidetone distorted, erratic operation: Weak battery. There is RF getting into
keyer; use an enclosure and shielded leads.
Can’t enter function mode: Pressing SW6 should put a logic low on pin 25 of
U1.
Can’t enter message mode: Pressing SW1, SW2, SW3 and SW4 should put a
logic low on pins 21, 22, 23 and 24 of U1, respectively.
LED not lit: Check the LED to make sure it is properly keyed to the silk-
screened outline. Check for 5 volts at R7 and a logic low on pin 18 of U1.
Keyer gives error beeps on function entry: Code characters must be perfectly
formed, with proper timing. Invalid command prefix or suffix.
THEORY OF OPERATION AND SPECIFICATIONS