Mend > Audio Systems

Mains Hum on Radio?

I have a Roberts RD-3 Digital Radio. When I plug it into the mains I get a loud humming sound. It doesn't matter what setting the Volume knob is on. If I turn the volume up, I can hear the radio station.

It happens on all sockets in the house and in my friends house. I've tried several different mains leads (with a figure 8 connection to the radio). In the plug, the Earth wire is not connected, but then that's what it says in the manual.

It works perfectly on batteries.

How can I fix the hum please?

s99raj
May 2015

Roberts Roberts RD-3 Audio, Audio Systems Radio Loud Sound

OK, thank you for that.

Since I'm not much good at electronics I have no idea what to look for if I was to open up the radio.

I'll either just carry on using it on batteries, or or get a new one.

s99raj
May 2015

I have answered you before - I made the mistake of thinking that the Power Supply was an external unit - so my suggestion of a new PSU or Power Supply Unit was inappropriate - sorry.

Nevertheless - internal or external - the AC to DC power converter inside your radio is defective - it should smooth out any mains frequency ripple but your radio's power circuit is obviously not doing that - you hear a mains frequency hum that can only come from the mains and must be on the power rail and should be filtered out by the smoothing section of the radio's PSU - but is not.

You can fix the hum by gaining access to the radio's internal workings and diagnosing the specific failure of the DC smoothing.

Good luck..
May 2015