parnass@ihuxf.UUCP (08/10/83)
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This news item concerns Kenwood 2 meter
transceivers. It:
o+ Describes a problem with the final amplifier
in a Kenwood 2 meter rig.
o+ Solicits comments from other Kenwood users.
o+ Mentions a modification to increase the
scanning rate in the Kenwood TR7800.
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I have been using a Kenwood TR7800 2 meter transceiver since
September 1980. It has given good, reliable service up
until yesterday, when the RF output of the transmitter began
to disappear.
The transmitter works fine for about a minute, then the
output goes flat. If the rig is turned off, and allowed to
cool, I can repeat the cycle over again. The culprit
appears to be the large, unserviceable, rectangular module,
designated M57733. This module contains the driver and
final amplifier transistors, and bolts to the rear heat
sink. Four wires emanate from this module:
o+ RF input
o+ RF output
o+ DC power for driver stage
o+ DC power for final stage
Kenwood quotes a price of $55 + $2.50 shipping for a
replacement part. I believe a similar module was used in
the earlier Kenwood TR7625, which has a bad reputation for
failure of this component. Has anyone had similar
experiences with TR7800's, TR7850's, TR7625's, etc?
The August 1983 issue of 73 Magazine contains an article
outlining a TR7800 modification which speeds up the scanning
rate. Most control functions in the TR7800 are handled by a
microprocessor. The clock for the microprocessor consists
of an LC circuit. The author doubled the clock frequency by
removing the slug in the clock inductor.
I applied this simple modification to my TR7800. It works,
and as a side effect, all the other operations controlled by
the micro are sped up also!
Robert S. Parnass, AJ9S (ARRL TA)
Bell Laboratories
Naperville, Illinois 60566
(312)979-5760
ihnp4!ihuxf!parnass