[Icom] IC-765 tuner problem

Thu, 09 Jan 2003 17:21:32 -0800

Hi Don,

There are several possibilities: either the reflectometer or its associated
phase comparator may have failed, or the tuner control processor may be off
in never-never land. There is also a service bulletin for correction of
tuner hunting by adjusting R5 and R7 on the tuner controller board (SB 03).

The IC-765 service manual , and an archive containing a number of IC-765
documents, including your IC-765 Notes and the service bulletin
(765sb03.pdf), are downloadable on the Icom FAQ site. You may wish to try
realigning the tuner, then performing the adjustment described in SB 03.

http://www.qsl.net/icom/manuals.html

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/
Icom FAQ site:
http://www.qsl.net/icom/

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of [email protected]
Sent: Thursday, January 09, 2003 13:14
To: [email protected]
Subject: [Icom] IC-765 tuner problem

Hello,

I've noticed that my IC-765 seems to have a problem with its tuner.
I was trying a new antenna and noticed that the tuner seemed to
stop at an SWR greater than 3:1 (on the 765's meter) with the
WAIT LED off and the TUNER LED on indicating a satisfactory match!
I switched to a dummy load and the same thing happened.
I thought that perhaps one of the motors had jammed so I removed
the cover and discovered that both capacitor gears were turning
but C17's gear (on the right when viewed from the front of rig)
was moving very slowly. So slowly that if I waited 45 seconds
it would eventually match the dummy load. No motor noise was
evident, so I had assumed that the tuner really had stopped
as the LED's indicated. After that I tried switching bands and
found that both motors turned at about the same speed. I went
back to my old antenna and found that everything seemed to work
properly. However, if I switch to the new antenna I can start
the whole problem sequence over again!

So it seems that the tuner gets into a state where some of it's
logic thinks it got a match (even though it doesn't) and C17
turns so slowly that it's imperceptible unless directly viewed.
That state persists even after a dummy load is connected.

The main external symptoms are the WAIT LED going off when the
SWR meter still indicates an SWR greater than 3:1. At this
point the tuner motor noise stops. The SWR then slowly drops
over a period of about 30 to 45 seconds.

Before I start taking things apart and adjusting things (i.e.
breaking things) has anyone else encountered this problem or
does anyone have any suggestions?

Thanks and 73,

Don

ve3hur
[email protected]
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