[Icom] IC-756Pro Heat Issues & Fan Servicing Information

Sun, 28 Apr 2002 16:13:41 -0700

George,

Not to worry! The thermistor is attached to Q5, one of the PA power devices.
70�C case temperature in an RF power device is hot, but not dangerous.

(In the matter of SI vs. Imperial measure, Napoleon won my war way back in
1955.)

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 Geo Clute W7LFD
Sent: Sunday, April 28, 2002 12:10
To: [email protected]
Subject: RE: [Icom] IC-756Pro Heat Issues & Fan Servicing Information

Thanks Adam for that great information.  Then according to below the
temperature of the IC-756PRO should never reach the 158 degrees F when in
receive mode and not transmitting, and if it does reach that temperature the
fan comes up at 158F.

If that logic is correct,  then it bakes the internals with a temperature
not exceeding 158F.

Geo W7LFD

Behalf Of Adam Farson
Sent: Saturday, April 27, 2002 10:11 PM
To: [email protected]
Subject: [Icom] IC-756Pro Heat Issues & Fan Servicing Information

<snip>
While transmitting, Q10 and Q12 are turned ON, and provide a voltage to the
cooling fan to rotate at medium speed. The thermistor detects the
temperature of
Q5, and activates Q11 and Q13 to accelerate the cooling fan when the
detected
temperature exceeds 70�C (158�F). The cooling fan rotates at high speed at
80�C
(176�F) or more.

The thermistor keeps the cooling fan rotating even while receiving until the
Q5
temperature drops to 60�C (140�F) or below.
<snip>