AdamQ Posted May 3, 2019 Share Posted May 3, 2019 I know there are some clever people on here, particularly when it comes to things electrical.I have a Roberts DAB radio (RD-76) which will only work when on battery power. I've tried a different - new - mains power adapter, but that hasn't helped.I've taken it apart and have noticed a load of green corrosion near a black doughnut-shaped thing (about the diameter of a two-pence piece) with copper wire looped round it on opposite sides - it's in the vicinity of where the power cable plugs in so the circumstantial evidence is strong. I've connected it up to the power supply and I'm getting 6V across the + and - soldered connections at the back of the socket. 6V is what it needs apparently (though it takes 6 × 1.5 batteries, so I'm slightly puzzled by that).I'm somewhat tempted to switch the adapter to 9V (it's adjustable) and hardwire the battery supply wires straight to the mains socket - are there any reasons why I shouldn't?And what is the doughnut thing - some sort of mini transformer? Maybe that explains the 6V vs 9V discrepancy ...?Obviously this does not carry the same urgency as the random knock/low oil pressure/high water temperature/strange vibration/pink smoke from exhaust ... the night before a track day, but if anybody knows about these things, it'd be good to fix it rather than bin it ...Thanks, Adam Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 3, 2019 Member Share Posted May 3, 2019 Can you add a photo of the doughnut thing and its connections?Can you tell if all of the batteries are connected in a single series? I wonder if two are used to power the memory...Jonathan Link to comment Share on other sites More sharing options...
Jim 123 Posted May 3, 2019 Share Posted May 3, 2019 I had something similar with a Sony. There is a small microswitch inside the jack plug socket for the power lead on some DAB's which disconnects the battery feed when the mains power lead is fully inserted. The switch can fail and not trip to mains-only feed when the jack plug is inserted. I found this out by using the tried and tested wiggle and thump diagnostic. Link to comment Share on other sites More sharing options...
AdamQ Posted May 3, 2019 Author Share Posted May 3, 2019 Jonathan, the memory idea for two of the batteries makes sense from a cursory glance at the wiring - thank you. Pictures below - the doughnut is ringed in blue in the second picture ...Jim, this definitely sounds like something worth investigating - inserting the mains lead causes it go silent when it's running on battery power so maybe it's only doing half the job - I shall wiggle and thump ... Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 3, 2019 Member Share Posted May 3, 2019 And what is the doughnut thing - some sort of mini transformer?I can't think why there'd be any AC in there... if it's near the power input possibly a choke to suppress any noise on that.Jonathan Link to comment Share on other sites More sharing options...
Ian B Posted May 3, 2019 Share Posted May 3, 2019 Is your mains adapter a genuine Roberts one, or a generic one?Check the polarity of the adapter as if JK's photo is the right one, it has a negative centre pin which is the opposite to what many generic ones are supplied as. Some allow you to remove part oft he connector and reverse it to change the polarity. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 3, 2019 Member Share Posted May 3, 2019 Doh! What Ian says: devices come both ways round.Jonathan Link to comment Share on other sites More sharing options...
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