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PK-232 TECHNICAL MANUAL
7.3.2.
Symptom: Modem cannot be calibrated
If the calibration signalis present, but you cannot seccessfully calibrate the frequency, the
value of a frequency-determining component may have changed.
o
Attempt the calibration procedures presented in Chapter 6.
o
Verify that the proper signals are present at U40 pin 2.
o
Verify the signal frequency with a frequency counter.
o
verfiy the values of the appropriate passive components.
7.3.3.
Symptom: Transmitter cannot be keyed
If the transmitter cannot be keyed and the
and causes the
o
The problem may be in the watchdog timer circuit at Q10 and Q3, or the PTT driver
transistors Q4 and Q5. Verify timing capacitor C55.
If
DCD Threshold
lighted:
o
The problem may be in the DCD Threshold circuits at U34. Verify variable resistor
R136 for an open lead.
7.3.4.
Symptom: Transmitted signals not copyable by other stations
If other stations are unable to decode your transmissions when using FM:
o
Verify the associated transmitter's modulation index. Verify that peak deviation at
any tone does not exceed 4 kHz.
o
Adjust the AFSK output level with R155 to produce the correct transmitter deviation.
If other stations are unable to decode your transmission when using an SSB transmitter:
o
Verfiy that the transmitter's audio input stage and ALC systems are not being over-
driven.
o
Adjust the transmitter's microphone gain in accordance with the radio manufac-
turer's duty-cycle, plate current and power dissipation specifications.
o
If reducing the radio's gain control does not solve the problem adjust the AFSK out-
put level with R155 to produce the correct transmitter operating conditions.
7.3.5.
Symptom: Received signals not copyable
If unable to correctly decode signals from other stations:
o
Perform the calibration procedures presented in Chapter 6.
o
Verify the correct settings of variable resistors R81 and R96.
o
Verify that the DCD Threshold control is operating correctly.
If the calibration procedure is satisfactory:
o
Inject a 1200-Hz test tone into J3 or J5.
o
Verify audio signal flow through switch SW2, C54, R34, U28-14 and U28-7.
PK232TM Rev. A 5/87
DCD LED
to be lighted or extinguished:
control has no effect on the
DCD Threshold
DCD LED
7-4
CHAPTER 7 – TROUBLESHOOTING
control functions normally
and the LED is permanently
Page 43
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Table of Contents
Troubleshooting
