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==============================================================================
K E N W O O D
>>> A M A T E U R R A D I O S E R V I C E B U L L E T I N <<<
==============================================================================
Kenwood Service Centers
Kenwood Service Corporation Kenwood Service Center, East
2201 East Dominguez Street 829 Lynnhaven Parkway, Suite 130
Long Beach, California 90801 Virginia Beach, Virginia 23452
Telephone 1-310-639-5300 Telephone 1-804-340-1702
==============================================================================
BULLETIN # 1002
MODEL: TS-450S/TS-690S
SUBJECT: Distorted TX w/TNC
Note: This bulletin supercedes bulletin ASB-994, dated April 10, 1992.
We have received several reports of distorted transmitter audio when using a
packet TNC controller such as the AEA PK-232 or Kantronics KAM, etc. The
symptom will generally disappear if the transceiver and TNC unit are powered
from different sources.
Cause:
The audio output level from the TNC is generally too high and causes
overload of the microphone amplifier circuit. In previous models such as the
TS-440S the incoming TNC audio was inserted after the microphone amplifier.
With the TS-450/690S it is inserted before the microphone amplifier. Just
moving the insertion point to the output of the circuit is not satisfactory
since the drive level for FM packet is higher than that required for SSB.
Procedure:
1. Add a 10 db attenuator to the PKD line on the IF unit (X48-3090-XX).
This will prevent overmodulation of the microphone input circuit.
a.Change chip resistor R233 from 10K to 18K ohms (RK73FB2A183J)
b.Change chip resistor R234 from 1K to 8.2K ohms (RK73FB2A822J).
c.Delete chip capacitor C173 (100pF) and add chip resistor R299, 1.5K
ohm (RK73FB2A152J)
2. Add the following note to page 35 and 37 of the Instruction manual.
3. When adjusting for proper ALC levels with an AFSK RTTY terminal or
Packet TNC terminal you should adjust VR-13 on the IF Unit for a
reading similar to the one shown in the accompanying diagrams.
Note: The transceiver and RTTY or TNC terminal should use separate power
supplies, in order to prevent RFI (Radio Frequency Interference.)
Caution: This modification requires soldering equipment rated for CMOS type
circuits. It also requires familiarity with surface mount soldering
techniques. If you do not have the proper equipment or knowledge do not
attempt this modification yourself. Seek qualified assistance.
Time required for this modification is 30 minutes or less.