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                        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

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BULLETIN # 1000
MODEL: TS-850S
SUBJECT: Distorted TX w/TNC Connected

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-850S 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 (X48-3080-XX). 
   This will prevent overmodulation of the microphone input circuit.
 a. Change chip resistor R258 from 2.2K to 1K ohms (RK73FB2A102J)
 b. Change chip resistor R260 from 220 to 330 ohms (RK73FB2A331J).
2. Add the following note to page 29 of the Instruction manual.
3. When adjusting for proper ALC levels with an AFSK RTTY terminal or
   Packet  TNC terminal you should adjust VR-18 on the IF Unit for a reading
   similar to the one shown in the accompanying diagram.

Note:  The transceiver and RTTY or TNC terminal should use separate power
       supplies, in order to prevent RFI (Radio Frequency Interference.)


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      (Initial Setting)

     ALC    -----------------
            X X X X X 0 0 0 0 0 0 0 0 0 0 0 0 

     SWR     

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.