Bit of a strange problem here, I was working on it all yesterday afternoon trying to source the problem with no luck.
The left channel of the quad amp is fine but the right channel is not. When you plug it in, music plays through the right channel for 2 or 3 seconds and then cuts out so I unplug it and after a few seconds the music comes back and then fades out again.
I've measured the main voltage and set that to 67, I've adjusted both mid-point voltages to 33.5 and set the quiescent current to about 10mA as per the service manual.
When there's no input signal, the right hand channel appears to be fine but when I put the signal in, I measured the output voltage before the capacitor and it stays around 33.5 for a second then increases quickly and saturates at 67V.
I measured the left hand channels output just before the capacitor for comparison with an input signal and that stays around 33.5V so there's something strangely wrong with the right hand channel.
Any ideas what the problem could be and where to buy replacement parts ?
Thanks, Louis =)
The left channel of the quad amp is fine but the right channel is not. When you plug it in, music plays through the right channel for 2 or 3 seconds and then cuts out so I unplug it and after a few seconds the music comes back and then fades out again.
I've measured the main voltage and set that to 67, I've adjusted both mid-point voltages to 33.5 and set the quiescent current to about 10mA as per the service manual.
When there's no input signal, the right hand channel appears to be fine but when I put the signal in, I measured the output voltage before the capacitor and it stays around 33.5 for a second then increases quickly and saturates at 67V.
I measured the left hand channels output just before the capacitor for comparison with an input signal and that stays around 33.5V so there's something strangely wrong with the right hand channel.
Any ideas what the problem could be and where to buy replacement parts ?
Thanks, Louis =)
Nevermind guys, I've fixed it 
I went through almost every part 1 by one comparing values with the working channel
C100, the input capacitor had gone funny so I put one of a similar size I had lying around and it works now
I'll go maplin and buy some replacements and replace all the capacitors, don't trust 40 year old capacitors
I went through almost every part 1 by one comparing values with the working channel
C100, the input capacitor had gone funny so I put one of a similar size I had lying around and it works now
I'll go maplin and buy some replacements and replace all the capacitors, don't trust 40 year old capacitors
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