PK-88 OPERATING MANUAL
TROUBLESHOOTING
6 - 4
PK-88 - 146
6.3.2.
Symptom: Transmitter cannot be keyed
If the transmitter cannot be keyed and the DCD LED is not lit:
o
Verify the watchdog timer circuit at TR3 and TR2.
o
Verify PTT driver transistors TR1, TR5 and TR4.
o
Verify timing capacitor C18.
6.3.3.
Symptom: Transmitted signals not copyable by other stations
If stations are unable to decode your transmissions when using VHF FM:
o
Verify your transmitter's deviation or modulation index. Verify that peak deviation at
any tone does not exceed 4 kHz.
o
Verify that your transmitter's modulation limiting circuits are not being driven into
limiting or clipping, and that both tones are being transmitted in the correct ampli-
tude ratio. A standard deviation meter should show the higher (Space or Start) tone
to be higher in amplitude than the lower (Mark or Stop) tone.
o
Adjust the PK-88's AFSK output level with the internal adjustment potentiometer
VR1 to produce the correct transmitter deviation.
o
Verify that your TXDELAY is long enough for the distant station's receiver to recover
from transmit mode and squelch. Increase your TXDELAY in increments of 10 (100
milliseconds) to see if the distant station's decoding improves.
If stations are unable to decode your transmissions when using SSB:
o
Verify that you're using the same sideband used by the other stations in your net-
work. (Although Packet-Radio produces the same results on either sideband, the
choice of LSB or USB may affect your radio tuning display or calibration.)
o
Verify 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 manufactu-
rer's duty-cycle, plate current and power dissipation specifications.
o
If reducing the radio's gain control does not solve the problem, adjust the PK-88's
AFSK output level to produce the correct transmitter operating conditions.
6.3.4.
Symptom: Received signals not copyable
If unable to correctly decode signals from other stations:
o
Verify that TONE is set for the proper modem tones.
o
Verify that the PK-88 is set to the proper HBAUD link rate.
o
Inject a 1200-Hz test tone into Pin 4 of J2.
o
Verify audio signal flow through C23, R18, U6 Pins 3 and 1, and that the audio tone
appears at U10 Pin 5.
6.4.
Terminal Interface Troubleshooting
If the PK-88 does not appear to start, respond to commands, or accept data from the termi-
nal, the problem may be in the RS-232C interface.
The following troubleshooting suggestions can aid in resolving problems related to the
RS-232C port.
