[Icom] A question of cooling.

Mon, 1 Jul 2002 08:32:59 -0400

Adam and Mike,
I have tried both the fan on the rear of the rig and dropping mains voltage
via a Variac.
Both solutions work well.  But there is one side effect of cooling down the
rig and this lies within the calibration of the CRT band scope.  It is
calibrated at the factory for the higher mains voltage in terms of the
higher temperatures generated and that is where the scope is centered on the
screen.
If I cool down the rig, the center freq. runs about 2.5 khz off center.
It's not a serious problem, but I would prefer it to be dead on.   The next
solution is to open up the rig and recalibrate it based on 105 volts or so
for the main input voltage.
I like to run the rig at about 105 since 100 is the minimum spec and there
is some variation on the mains here based on service loads at the power
company.  I have also tested running it at 112-115 v  to see how she centers
on the scope and it is the same off center problem.  At 120 to 125 v, it
centers.

Hope all is well with you and Mr. MacGiver Adam. Talk to you soon
73, Bruce K1XR

----- Original Message -----
From: "Adam Farson" <[email protected]>
To: <[email protected]>
Sent: Sunday, June 30, 2002 2:35 AM
Subject: RE: [Icom] A question of cooling.

Hi Mike,

The power-supply heat problem in the IC-781 is a matter of concern. 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 (PI) area runs very hot. This can lead
to component breakdown over time. Further reading:
http://www.icomamerica.com/support/troubleshooting/ic-781.html

Bucking the mains voltage down to 100V via an autotransformer (minimum
rating 1 kVA) is probably the best solution.

My IC-781, which was in my station from mid-1993 until late 1998, showed a
significant temperature rise around the PI (power regulator) area, and also
in the CRT module. At a 28�C ambient, the PI heatsink temperature rose to
60�C after a couple of hours. The CRT area also appeared to be a major heat
source.

I did not wish to modify the radio, as this would almost certainly have hurt
its resale value. instead, I set up a 20 cm diameter table fan behind the
radio, and on the left-hand side. I turned this fan to blow a stream of air
across the PI and PA heatsinks.

As a result, the PI temperature dropped from 60�C to about 40�C.

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/
Note new e-mail address:
mailto:[email protected]

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Michael P. Olbrisch
Sent: Saturday, June 29, 2002 04:54
To: _ICOM_list (E-mail)
Subject: [Icom] A question of cooling.

Good morning,

I just got done pulling annual maintenance on my IC-781.
Replaced the battery, brushed out the dust, stuff like that.

Now the questions.  Time for the experienced experts to
weigh in on another idea.

Several individuals on this list have mentioned that the
IC-781 runs hot.  Of course, mine is no exception.  I have removed
the speaker and speaker cover long ago to allow better air flow
as some have mentioned.  I also have a small muffin fan gently
blowing on the regulator area of the back.  This helps, but it is
still warm to the touch.  I have considered regulating the AC power
to 100 volts, but have not done that yet.

In cleaning the radio, I did remove the covers to the
regulator and final areas to remove dust.  I noticed that while
the final area is vented, the regulator area is not.

At work I have the equipment to punch holes in metal.
Nice heat holes, from 1/16th inch up to 2 inches or larger.  I
was wondering, anyone think it might be good for the heat
problem to punch a few holes in the upper and lower areas of
the regulator cover to aid in cooling it?  If so, would this have
an adverse effect on final cooling?  I expect I would use the
1/4 inch punch, and 5 or 6 holes both upper and lower.

All comments welcome.  Thanks for taking the time to
send your opinions.

Mike.

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