Re: Radio goes deaf when changing frequencies


Steve W3AHL
 

If the previous suggestions don't help isolate the problem, it probably needs to trace the signal level from the antenna input through the IF sections to see where the problem is.  But it's probably not something you can repair and a Service Center would probably do a board replacement, which can be expensiive.  

Here are some random thoughts came to mind, but none converge on all of the symptoms you described:

  1. Since it seems to be heat related, a can of cold spray might help isolate it.  The DDS board would be my first guess, followed by the LOGIC board, then the MAIN. 
  2. Does changing the AGC setting affect the symptoms any?  Especially turning it off.  Page 74 of the manual.
  3. Since you seldom transmit, the relays on the PA board that select the correct low pass filter based upon tuned frequency may have accumulated oxide on the contacts and not make a good connection for the sub-microvolt received signal.  Transmitting into a dummy load on 160M-10M at full power for 30 seconds at a time, making several cycles through the bands might help.  But some of your symptoms don't make this seem like them real problem.
  4. The small gray coaxial cables that connect the DDS to the MAIN board can become intermittent.  Wiggling & pulling on both ends of the cables near the connector might make the problem better or worse.  If so, replace the cables.
  5. Are there any other subtle symptoms that you have seen?  Do VHF and UHF seem to work OK?  Any smells of overheated components that you noticed when the problem started getting worse?
Steve, W3AHL


On Sat, Mar 24, 2018 at 05:39 pm, Scott Remington wrote:
Hello All:

I've had my IC-7k for several years now and seen very little transmit time.  Mostly I use it to (try to) listen to the Shortwave Radiogram transmissions on the weekend.  A few months ago I began noticing that right after I turn the radio on and when it's cold, the receiver would go deaf when I change frequencies with the dial.  I'm not spinning the dial very fast and most of the time I'm in AM mode and anywhere from 5 MHz to 20 MHz.  Basically the background noise is reduced in level.  When this happens, I simply power cycle the radio and receive sensitivity comes back.  I got around this problem by simply turning the radio on Friday evenings to let it warm up and be ready for the weekend activities.  Lately it's gotten a LOT worse.  Tonight I could barely go more than a few kHz before sensitivity would go away.  I've also noticed that at times AM transmissions just don't sound "right".  I would switch to either LSB or USB and could tell the radio was off frequency.  Power cycling again and sideband reception sounds just like AM (well, as close as a dual sideband AM transmission could).  There's a local AM transmitter a couple miles from my home and before I could tune to the station and listen without issue.  It would be 60+ dB over but I could still receive it.  Enabling the attenuator dropped the signal strength as expected.  Tonight however, there was nothing I could do to bring that station in.  As I tuned toward it, the signal level would rise quickly and then the radio would go deaf.  If I enabled the attenuator, still deaf.  If I power cycled with the attenuator enabled, I'd get a fraction of a second of audio before it would go deaf.

Any ideas what could be going on with this thing?  This radio has had a pretty sheltered life and when it's been off, the antenna has been grounded, so I'd most likely discount any static hits.

Thanks in advance!
AA7SR

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