Subwoofer Power Supply

D Vautier
made 1-12-2013

My sonís subwoofer blew out.  He has a Polkaudio RM6880.  There are other components to the set but they are whimpy so he only uses the subwoofer with a low level signal from his big receiver.  When the unit failed I looked inside  and noticed the 1 amp fuse was blown.  this looked easy but there's no such thing in electronics.  I replaced the fuse and it blew again as i expected so I tried a 5 amp fuse which held but blew out the transformer primary coil which had been obviously shorted.  When I put the bigger fuse in the circuit heated up, smoked, stunk and finally opened.  The transformer was labeled 86H-4102 DCGM 0725A.  My suspicion was that the two secondaries were around 12 volts AC or enough for the board to rectify to 12 volts DC.  The transformerís primary coil was shot as well as both secondary coils so there was no way to test impedence of to find out anything.  I tried to get specs on this transformer and could find absolutely nothing anywhere anyhow.  Nor could I find voltages required to drive the control board but I estimated 12 volts looked good.  I went to the local electronics store and scrounged around in their surplus room and located a transformer that looked more or less close to this bad one.  I tested the primary and secondary coils on the surplus unit and they were OK.  The transformer took 110 volts through the primary coil with a 1 amp fuse.  I have no idea what voltages were needed but I hooked the secondaries up to the subwoofer control board and everything worked fine.

It would be wonderful if companies published their wire diagrams and specs but sometimes you just have to guess or buy a new one.