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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 # 994
MODEL: TS-450S/TS-690S
SUBJECT: Distiorted TX Audio with TNC
We have received several reports of distorted transmitter audio when using
a packet TNC controller such ts 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 TS450S/690 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 20 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 capicitor Cl73 (1OOpF) and add chip resistor R299, 1.5K ohm
RK73FB2Al52J
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 for a reading similiar to the
one shown in Figure 2.
Note: The transceiver and RTTY or TNC terminal should use separate power
supplies, in order to prevent RFI (Radio Frequency lnterference.)
Caution: This modification requires soldering equipment rated for CMOS
type circuits. It also requgres familiarity with surface mount soldering
techniques. If you do not have the proper equipment or knowledge do not
attempt this modificatlon yourself. Seek qualified assistance.
Time required for this modification is 30 minutes or less.
Figure--
S 1 3 5 7 9 20 40 60
X X X X X X X X X X 0 0 0 0 0 0 0 Set 50 Watts with
5 dots on ALC scale
Power 0 10 25 50 100 150
ALC -----------------
X X X X X 0 0 0 0 0 0 0 0 0 0 0 0
SWR