[Icom] 765 TR relay

Wed, 5 Mar 2003 22:11:02 -0500

Adam.  Gosh, I do indeed thank you for all of that very helpful
information.  I am going to try the external mod first as you suggest
and see what it does.  If it helps, I will look into the more permanent
mod.  And I have been debating and debating doing the pass band mod for
quite a long time now.  I may finally be moved to do it.  80% of my
operating is CW and I guess I haven't found the mod as necessary as it
probably is for SSB.  On the other hand, I do use the pass band on my
756 PRO from time to time.  It is very effective on SSB and CW.  But, of
course, the filter skirts on that radio are so steep that moving the
side of the filter just a little bit really makes a difference.  The 765
skirts are not as sharp by a long shot.

Now if there was only a mod to make the broadcasters go away on 40
meters at night . . . . 

Thanks again for the fine information, Adam.

Bruce - W8FU

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Adam Farson
Sent: Wednesday, March 05, 2003 2:16 PM
To: [email protected]
Cc: GEORGE T. BAKER
Subject: RE: [Icom] 765 TR relay

Hi Bruce,

Looking at the schematic of the ANT SW UNIT (IC-765 service manual, p.
9-3),
the receive signal-path switching relay RL201 may be the culprit. This
relay
operates, and connects the RF IN/OUT jack J204 to the RANT OUT jack J205
on
receive. If the RL201 contact is flaky, you will experience the
intermittent
you describe.

Replacing the relay (Icom Part No. UPM-12905Y) may be the best option.
If
you wish to install a wetting-current resistor, you can connect a 10K
0.25W
metal-film (not carbon) resistor between the +13.8V rail (P203 Pin 5)and
the
centre pin of J205.

You can first try connecting the resistor externally between the +13.8V
accessory socket and the centre pin of the RX ANT IN jack on the rear
panel.
A neat way to accomplish this is to fabricate an RCA-ended mini-coax
jumper
with the resistor connected to the centre conductor, and a 0.01 uF disc
ceramic cap between the other end of the resistor and the braid. The
other
end of the resistor is connected to +13.8V. If this "lash-up" cures the
intermittent, you can then go to a permanent mod.

I am e-mailing you separately a Zip file containing scans of the ANT SW
schematic and board layout. Also, there is a service bulletin which
involves
adding a 0.0047 uF 500VV disc ceramic cap between the junction of R201
and
L201 on the ANT SW board. This mod may already be present in your radio.
This service bulletin, along with the W2ISB PBT Mod and many other
IC-765
documents, is downloadable here:

http://www.qsl.net/ab4oj/download/download.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 Bruce D. McLaughlin
Sent: Tuesday, March 04, 2003 15:42
To: [email protected]
Subject: [Icom] 765 TR relay

Well, I think my faithful 765 may be developing arthritis of the TR
relay.  After a few minutes, it sometimes loses sensitivity on receive.
If I send a dot or dit, the sensitivity immediately comes back.
Sometimes it remains OK for the rest of the session and sometimes I have
to dit again once or twice.  Does that sound like TR relay trouble?

If it is trouble with the TR relay, how much of a problem is it to
replace.  I don't have a service manual unfortunately so I am trying to
make a preliminary assessment as to whether this is something I could
reasonably do myself.

Bruce - W8FU

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Icom Users Net: Sundays, 1700Z, 14.315 MHz
Icom FAQ: http://www.qsl.net/icom/

----
Your Moderator: Dick Flanagan W6OLD, [email protected]
Icom Users Net: Sundays, 1700Z, 14.315 MHz
Icom FAQ: http://www.qsl.net/icom/