[ICOM] IC-756PROII problem on 6 meters

[Paul Playford]

I had similar symptoms on my PROII a couple of years ago.  

In the process of finding the problem I destroyed a few other components but
the trouble originated with C131 on the RF-A unit shorting which took out
D131, D141 (D141 was OK but easy to change) and D153, which caused the radio
to be in receive (also) during transmit, creating a feed back loop which is
after the ALC.

These devices are on the bottom of the RF-A unit and very easy to get to.

The service manual is available for download on the Icom web site and the
parts from Icom are very inexpensive.

de Paul, W8AEF


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Mark Mumaw
Sent: Friday, February 04, 2005 5:27 AM
To: icom at mailman.qth.net
Subject: [ICOM] IC-756PROII problem on 6 meters

    I am having problems with my PRO II on 6 meters transmit.  On SSB with
NO drive, the transmitter takes off displaying full ALC and high SWR and low
power out. This occurs even with the mic disconnected and mic gain and RF
power at full ccw position. It also does it in all modes. Sometimes it will
correct its self after the radio heats up. It appears that the PA is self
oscillating. It generates a large signal at approximately 44.6 MHZ no matter
what the VFO setting.

 

  Any ideas on how to repair this????

 

Thanks ..Mark NU6X   

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