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In Reply to: SS Amp doesn't play until loud signal posted by erik_squires@hotmail.com on March 27, 2007 at 12:13:19:
...clean the volume and other pots and check all the other connections.
Follow Ups:
Thanks for your advice!But it turned out to be the output protection relay.
It's obsolete, so I removed it and jumpered around it. Sounds great in the surround channels. :)
I have three Yamaha B-2's and had to replace the speaker protection relay on all three for the very same reason. Are you sure the relay is obsolete, the one's in the B-2's are Omron's and are still available from Digikey. Also since you bypassed it your not sure if the relay is bad or not. There is a zener diode that holds the 12volts for the relay and they tend to get weak. If you can get a relay, I'd change the zener too.
Unfortunately the relays in the P2075 are MS4Us from DEC, which still makes similar models, but I can't find a stocking dealer in the US.Looking at the disassembled original, it look like they started life as a 4PST Normally Open, 600 Ohm, 24VDC relay. There are 4 input pins (towards the amplifier) and 2 output pins (towards the speaker terminals). The relay soldered the 4 reeds together internally, probably a way to make the relay more reliable. Both reeds would have to fail before the speaker would fail to connect. I'm not sure why Yamaha didn't just bridge the output pins on the circuit board instead of inside the relay. This would have allowed them to use VERY off the shelf parts. I wonder if back then the cost of the extra two holes mattered to the overall cost.
Fortunately, I'm pretty sure that a standard Omron 24VDC 600 Ohm 4PDT relay (MY4 24VDC) will work. I had to order a PCB mount socket for it, now all I have to do is drill a couple of additional holes in the PCB, and bridge those extra output pins underneath and this amp should be good for another thirty years.
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