Expert: Cleggsan - 3/17/2009

Question
I have a sony music system which has a 2 or 4 speaker output,yet neither of my right hand speaker outputs work,I have checked all fuses, circuit boards & wires but can not see any obvious faults,yet when I switch on all I get from the right hand outputs is a thud and a low level; hum,the left hand outputs are ok, I am having to use both of my left hand speakers,what I need to know is what the problem is likely to be so I can fix it I have asked 3 people already without success, can you please help

Answer
You did not give me a model number so it is impossible for me to give you a specific suggestion.

But, I can give you some general ideas from which maybe you can figure out what is going on.

ONE:  First, switch the speakers;  left to right and right to left.  If the troubles switch over then the problem is in the speakers.  (For example, it is possible one or both of the right hand speakers are shorted out.)

TWO:  Disconnect only one of the right hand speakers, then the other.  It is possible one is defective and not the other.

THREE:  If the speaker switching and testing confirms the speakers are not the problem then you must assume the problem is internal to the amplifier.  Most common failure is the audio output amplifier itself.  It may be a power module or individual output transistors.  But the devices are likely mounted on or in some way connected with a heatsink.  That will help you identify the section on the board.  Just follow the speaker output wires back into the point where it they connect into the board - that will help you identify the output section of the unit.  

FOUR: If you think the output amplifier is defective and you have a voltmeter, disconnect all speakers and measure the dc output on the speaker terminals (no audio; volume control set at zero) and if there is a dc voltage of more than a few millivolts then you know that amplifier section is out of whack.

FIVE:  The power supply for the right side amplifier can also be defective.  You can use the voltmeter to check the dc voltages by comparing the dc at the output amplifier on the right and then the left channels.

This should guide you to the right conclusions as to what needs to be repaired.

Good Luck,

c