[Icom] 765 TR relay

Wed, 05 Mar 2003 11:16:01 -0800

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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