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World of Ham Radio 1997
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WOHR97_AmSoft_(1997-02-01).iso
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1997-02-01
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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 # 957
MODEL: TH-75A
SUBJECT: NO TX ON VHF USING A VEHICLE BATTERY SUPPLY
When the TH-75A is connected to a vehicle battery, ignition or alternator
noise can be induced on the DC line. When the transceiver is in the
automatic battery saver mode, the noise pulses overcharge C348 on the RF
board causing it to short. The supply current opens L218 and the foil
trace at this coil. To protect the transceiver, a Zener diode will be
used to clamp the SBR line.
The Zener should be soldered between the SBR side of L218 and the shielding
case of L221 on the component side of the RF board (X53-3370-11) (A/3).
The Service Manual disassembly instructions will be required to perform
this modification.
NOTE: This modification has already been performed on models starting
with serial number 007XXXX.
REQUIRED PART: 22V ZENER DIODE - KENWOOD PART # UZP-22B
This is an optional change that is not covered under warranty.
Time to perform this modification is 1 hour or less.