Yamaha A -960 repair

robotc

New Member
I am currently repairing a Yamaha A-960 amplifier. One issue was a burnt out power switch that needed replacing. The original switch is mounted on a small pcb but the only replacement switches I could find did not have pcb pins. The new switch works fine but on the original switch there is a shielded wire connected from the main switch through two 680pf capacitors mounted on the pcb to the secondary of the transformer. (See image)
Capture.JPG
I am in Australia but this connection is not present on the US or Canadian circuit diagrams in the service manual. I guess the line voltage and/or frequency are the reason for this
I have a couple of questions
What is the purpose of this connection?
The amplifier seems to work without it so is it ok to leave off this connection or do I need to find another way of connecting the capacitors to the switch?
Thanks
Robert
 
As for your question about the coaxial cable. I'm not sure and would need to see the schematic you are looking at. The partial you posted is to small for this old man to read.
 
Thanks for the promp replies. I am aware of the capacitor issue -it was already burnt out when I got the amp - and that has been replaced. I have also carried out the zener +resistor bypass of the indicator lamps. So the amp works fine now.
Here are a two larger circuit diagrams that might be easier to read.
Capture1.JPG Capture2.JPG
 
AC signal feedback perhaps.SWAG:biggrin:..Not sure. Maybe has something to do with 50Hz mains frequency.Don't see that over here in 120v 60Hz land.
 
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