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Author Topic: ic-735 gone deaf from 2 to 4 Mhz  (Read 471 times)
VO1FZ
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Posts: 71




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« on: January 05, 2010, 03:37:20 PM »

My Icom IC-735 has been doing great until a couple of days ago when I noticed 80 meter receive is so low it doesn't even move the S meter.  When I tune the VFO, it receives normally below 2 Mhz and above 4 Mhz.  A relay clicks in as I go past 2 and again at 4.  All between 2Mhz and 4Mhz signals are down quite low.  The signals are there, but low.  There is a major difference as the relay kicks in on 2 and 4.

Transmit is normal.


Just wondering if anybody has any ideas?
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K6SI
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Posts: 12




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« Reply #1 on: January 05, 2010, 06:42:19 PM »

Perhaps dirty relay contacts.
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TANAKASAN
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Posts: 933




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« Reply #2 on: January 06, 2010, 07:11:41 AM »

OK, so you hear a click but this could be unconnected (pun, sorry)

I don't think the IC-735 has an automatic ATU so the noise could not be that. If you look at the schematic you will see that the low-pass filters each have TWO relays and if only one switches or makes contact then this will produce the symptoms you describe.

Check very carefully around the 2 MHz - 4 MHz low-pass filter.

Tanakasan
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TANAKASAN
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« Reply #3 on: January 06, 2010, 07:13:50 AM »

Hang on, are you SURE that transmit output is normal?

T
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VO1FZ
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« Reply #4 on: January 06, 2010, 08:22:02 AM »

Thanks T.,
I haven't had an audio check on the transmit signal from my 735, but it is producing full power output.
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N4OGW
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Posts: 288




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« Reply #5 on: January 06, 2010, 10:07:57 AM »

There is a common problem with some trimmer capacitors in the 735 and other similar age Icoms. This will wipe out one or more bands completely. Google "trimmer capacitor icom" for details.

But if your transmit is really working fine it might be something else. Can you or someone else listen to your transmit signal?

Tor
N4OGW
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VO1FZ
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Posts: 71




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« Reply #6 on: January 11, 2010, 03:07:28 PM »

I guess I now have a small correction to my original problem.  My receiver is now totally deaf from 3.0 to 3.999 Mhz.

I'm suspecting trimmer caps now, but have a further question.  Namely, the rig is still transmitting fine on frequency.  Is that normal if the problem is trimmer cap related?

Thanks,

Keith
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