[Icom] Heat in the IC-781 and others.

[Adam Farson]

Mike,

As you are doubtless aware, the power-supply heat problem in the IC-781 is
quite serious. The power supply uses a shunt regulator, and was designed for
the Japanese 100V mains supply. When connected to 120V mains, the power
supply dissipation increases by 20%. The heatsink was not designed for the
additional thermal load; consequently, the power-supply area runs very hot.
This can lead to component breakdown over time. Further reading:
http://www.icomamerica.com/support/troubleshooting/ic-781.html

The CRT module is another heat source. Over time, several resistors on the
CRT board can overheat and char the board.

When I had an IC-781 in my shack, I helped it "keep its cool" by setting up
a 20cm diam. table fan to blow a high volume of air across the heatsink at
the rear of the radio. To reduce heat generation, you could combine the
external fan with a 100V mains supply to the radio (derived from a 2.5 kVA
bucking transformer, obtainable at any electrical supply house). The bucking
transformer should be configured to buck the 120V mains by 20V.

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/
Note new e-mail address:
mailto:farson@shaw.ca



-----Original Message-----
From: icom-admin@mailman.qth.net [mailto:icom-admin@mailman.qth.net]On
Behalf Of Michael P. Olbrisch
Sent: Wednesday, February 06, 2002 08:36
To: _ICOM_list (E-mail)
Subject: [Icom] Heat in the IC-781 and others.


Howdy fellow Icom-ers,

	I will be pulling my IC-781 out of the operating position
in a few days to give it its annual cleaning, and to replace the
old battery.  I know the 781 runs hot, I have had a fan blowing
on the heat sink for years now.  But this will be a perfect time
to look at improving on it if I can.  In the past, I have heard
several suggestions here on the list, but I do not remember them.
If you have a 781, or another like it, how have you fixed the
heat problem?

Mike.  KD9KC