My Icom IC-M402 has developed a bad habit of "sticking" on CH 73 when it should be scanning. Doesn't stick on CH 16, 12 or 72. Altering squelch does not fix it. On 73, it produces white noise, similar to low squelch in normal ops. Any thoughts from the tech department??
Does it still do it when EVERYTHING else on the boat is switched off?
You may have something that's electrically noisy (laptop, tablet, charger, inverter, etc) that might be hitting that frequency with some interference. Hence the scanner stops at that channel.
Also does the scanner have a way to mute that channel (ie exclude it from the scan)?
It is also possible that a repeater station in your area is using this same frequency, thereby stopping the search function from continuing to cycle through.
Unplug the antenna and see if it still does it. That will tell you if the bug is in the radio or an actual signal.
Select to expand quotenebbian said..
Does it still do it when EVERYTHING else on the boat is switched off?
You may have something that's electrically noisy (laptop, tablet, charger, inverter, etc) that might be hitting that frequency with some interference. Hence the scanner stops at that channel.
When in dock, nothing else except solar controller. Will think more about ruling out other boat sources of RF signal. Does it both inside Queenscliff marina and out in PPB.
Also, thanks Trek. Difficult to unplug antenna, as radio is fully mounted, but will give it thought. Bruski, I don't think CH 73 is repeated. My info is that repeaters are on 21, 22, 80, 81, 82.
Another simple diagnostic test might be to buy yourself a hand held marine VHF which are very handy as a backup and see if it does it too. If yes then you probably do have a stray signal.
LIke nebbian said theres heaps of interference sources these days because of switching voltage regulators, they are even in some LED nav lights and probably in your solar regulator if its an MPPT type. In theory they should meet a standard where RF emissions are so low they dont effect radios but no one tests them 
I knew someone whos radio got noise across all channels and it was from a new masthead light with a switching voltage regulator in it.
Select to expand quoteTrek said..
Unplug the antenna and see if it still does it. That will tell you if the bug is in the radio or an actual signal.
It's possible that the interference is not coming in via the antenna, I don't want to get into superheterodyne theory but it is possible to have interference coming in through other means than the antenna, it doesn't have to be at the frequency that the scanner is stopping at either. The way I'd test would be to turn EVERYTHING else off (possibly even just power the radio via a handheld battery if it's not easy to turn everything else off) and see what happens.
If the interference is not coming in through the antenna, which can be proven by unplugging it, then there is a fault in the radio.
The receiver should only be detecting signals detected from the antenna plugged into the antenna socket. If a signal gets in any other way or is internally generated there is a fault in the radio or at best a poor design. Superheterodyne or not. 
Found the source of the problem. It only happens in Queenscliff Harbour, and disappeared once outside in PPB. Ops normal at sea - so all good again. I even just received Tasmanian base station announcing weather broadcast on Ch 16.
