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World of Ham Radio 1997
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WOHR97_AmSoft_(1997-02-01).iso
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asb1048.txt
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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 # 1048
MODEL: TH-78A
SUBJECT: IMD Improvements
Symptom:
When the transceiver is subjected to a strong electric field, such as might
be encountered near an FM Broadcast Station, TV Transmitter or near Land
Mobile sites, the sensitivity might be lowered, scanning operation may
become difficult or impossible, distortion of the desired signal may be
encountered or problems with the S-Meter circuit may become apparent.
Corrective Action:
Change of the components indicated in the chart on the TX-RX Unit
(X57-4090-XX B/4) will reduce mixer currents and reduce the bandpass of
the Band Pass Filter (BPF) circuit.
Parts Required:
Qty Description Kenwood Part No. Circuit Description
1 1 k ohm chip resistor RK73GB1J391J R80
1 3.3 k ohm chip resistor RK73GB1J332J R81
1 3 pF chip capacitor CC73GCH1H030C C100
1 18 pF chip capacitor CC73GCH1H180C C116
1 10 pF chip capacitor CC73GCH1H100D C155
Procedure:
1. Change R80 from 390 ohm to 1 k ohm.
2. Change R81 from 3.9 k ohm to 3.3 k ohm.
3. Change C100 from 1 pF to 3pF.
4. Change C118 from 33 pF to 18 pF.
5. Change C155 from 1000pF to 10 pF.
This modification required advanced surface mount soldering equipment that is
rated for CMOS circuits. It also requires familiarity with advanced surface
mount soldering techniques. If you do not have the proper equipment or
knowledge do not attemt this modification youself. See qualfied assistance
from your nearest Kenwood Service Center (Long Beach, Ca. or Virginia
Beach, Virginia)
Time required for this modification is 60 minutes or less.
Service Code A: 18 B: X57-4090B/4 C: R80 D: 91