Help - Hum in transmit SSB audio

[AD8J]

I've been using my Remote Rig pair with a TS-480 for over 4 years with no SSB transmit audio problems.  All of a sudden, I have a very loud hum being transmitted.  CW is fine.  If I take the control head to the remote site, the transmit audio is fine.  I replaced the 12 volt power supply for both RRC's but no change.  I also replaced the 8-pin mic cable between the radio RRC and the rig but the hum is still there.  If I reduce the mic gain to zero, the problem goes away but I have no transmit audio.  The higher the mic gain, the higher the hum.   Using both normal audio and processed audio results in the same hum.  If the TX monitor is in the off position, the hum is reduced slightly.  If I increase the TX monitor level, the hum increases.  If I key the transmitter, in SSB mode, without a mic, the hum is still there.   I normally run the RRC audio configuration at setting 5.  I tried 2 and 7 but it didn't change anything.  I've run out of things to try.  Does anyone have a suggestion?

[dj0qn]

Since no one else has responded, I will give you my tips.....

First of all, this problem is not caused by any settings in the RRC, it is hardware related. Don't waste your time
trying different settings.

Now on to what can be causing this. Like I said, it is hardware related. Some places to look:
- Most likely culprit is a power supply. Since you said you already replaced them, make sure also that any extension
plugs or whatever they are plugged into are also not the problem.
- remove or swap the microphone and see if that makes a difference
- Check all cabling to make sure they are tightly connected and that no wires became broken
- Make sure that the red straps inside of the RRC's are well placed and none came loose

73,
Mitch DJ0QN / K7DX

[AD8J]

Mitch:  Thanks for your suggestions.  Today I checked all the red jumper connections and replaced the power supply that feeds the rig.  I still have hum.  I think I'll make another trip to the remote site and take the UPS out of the circuit.  I'll also take a close look at the power strips and the cabling.

[AD8J]

I removed the UPS and put all the different power supplies on the same circuit.  Still had hum in the transmit audio.  As a last resort, I replaced the TS-480 at the remote site and didn't have any hum.  But later on, it was back.  I have the red jumpers configured as "Connection type 1" and it has been that way for years.   Grasping at straws, I'm wondering if I should be using "Connection type 2".  The instructions say use "1" for serial numbers after 70600056.  My serial numbers are:  B4300087 and B1400107 which doesn't make sense with the all number serial number mentioned..  The radios were purchased in 2011 and 2014.  Can anyone confirm if my radios are older (Connection 2) or newer (Connection type 1)?

[AD8J]

I found the answer to my question at:  http://www.g4gcp.co.uk/TS-480/kenwood_serial_numbers.pdf    My radios are the newer ones and use Configuration type 1.  I'll recheck the jumpers at the remote site tomorrow.

[AD8J]

Yesterday I made three trips to the remote site, trying different things to get rid of the hum.  Having replace just about everything, I replace the radio and the hum was gone.  By the time I got home, it was back.  Today I finally found the problem.  It appears that when I put the mic jumpers in place on the remote site RemoteRig unit, I reversed the mic and ground.  For some reason, it worked for many years before developing the hum.  Now that I have it wired correctly, some other things that I figured were just part of operating remote corrected themselves.  I can now monitor my own transmitted audio and have better control over the recording and playback levels in the voice keyer.  The mic gain and processor level controls seem to adjust better.  Having just made 75 contacts in the phone DX contest, I am considering this problem solved.

[dj0qn]

Glad to hear the good news!

73,
Mitch DJ0QN / K7DX