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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Yamaha R-900 Receiver Protective circuit relay question
I have a Yamaha R-900 Receiver that has worked flawlessly up until
about a week ago. About one out of four times that I switch it "on" the protective circuit relay does not engage. Also, if I leave it on for several hours, the receiver will shut down. Any suggestions? Thanks, Mark |
#2
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If I remember correctly, there's a small electrolytic cap in the
mains detection section of the speaker protection circuit which goes open circuit. It's maybe 1uF or 10uF... years since I worked on those. I don't know why the unit would shut down after a few hours though. Good luck with it. Cheers, Bob wrote: I have a Yamaha R-900 Receiver that has worked flawlessly up until about a week ago. About one out of four times that I switch it "on" the protective circuit relay does not engage. Also, if I leave it on for several hours, the receiver will shut down. Any suggestions? Thanks, Mark |
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wrote in message oups.com... I have a Yamaha R-900 Receiver that has worked flawlessly up until about a week ago. About one out of four times that I switch it "on" the protective circuit relay does not engage. Also, if I leave it on for several hours, the receiver will shut down. Any suggestions? Thanks, Mark You may have a component that breaks down with heat. Use a hair blow dryer in the pertinent area. When the receiver shuts off, spray the area with coolant, using the nozzle insert tube to focus on individual components. A little practice and you can become a pro troubleshooting thermal problems. Good luck and remember the aforementioned is only 1 possibility, but I believe a good starting point. Good Luck and Happy New Year. Cordially, west |
#4
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This is not quite a tube issue but I think I can help you. The offset
voltage adjust is set to borderline operation. i.e. there is approximately 50mV at one of the speaker outputs. Yamaha had two pots per channel for adjustment. One was for idle current and the other for this offset adjust. Your speaker protection circuit is sensing this offset and turning on and off depending how bad it is. Carroll wrote in message oups.com... I have a Yamaha R-900 Receiver that has worked flawlessly up until about a week ago. About one out of four times that I switch it "on" the protective circuit relay does not engage. Also, if I leave it on for several hours, the receiver will shut down. Any suggestions? Thanks, Mark |
#5
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Hi Carroll,
Sorry if a question about a solid state receiver seems a bit off topic for this "valve" ng... But there is a wealth of talent, knowledge and experience posting to this ng. Due to the age of this receiver, I was/am hoping that someone would have the information to point me in the right direction. Most of these "tube gurus" have forgotten more than I will ever know about tube gear, and some of the same tube guys also serviced early solid state audio equipment. I do appreciate any and all input, Thanks, Mark |
#6
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Bad idea suggesting this person adjust his own amp with no training or test
equipment. Yamaha's trigger at about 1.2 volts. If there's this much offset, the amp needs service - period. The problem could be a bad cap in the feedback circuit, we've seen this before. Mark Z. Authorized Yamaha servicer "Carroll Conklin" wrote in message ... This is not quite a tube issue but I think I can help you. The offset voltage adjust is set to borderline operation. i.e. there is approximately 50mV at one of the speaker outputs. Yamaha had two pots per channel for adjustment. One was for idle current and the other for this offset adjust. Your speaker protection circuit is sensing this offset and turning on and off depending how bad it is. Carroll wrote in message oups.com... I have a Yamaha R-900 Receiver that has worked flawlessly up until about a week ago. About one out of four times that I switch it "on" the protective circuit relay does not engage. Also, if I leave it on for several hours, the receiver will shut down. Any suggestions? Thanks, Mark |
#7
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Hi Mark.
Your point about a novice is a good one. I have no intention of tampering with something as nice as this unit, and possibly causing more harm than good. I have a couple of "junkers" that would make better learning fodder... However, I do have a couple of friends that serviced Vacuum tube/early solid state equipment, and they have helped me in the past get audio gear up and running. They have been more than gracious in their aid to help, but I hate to impose on them. So, by posting on this ng, I can get a better better grasp of electronic circuitry, and narrow down what the trouble with a unit might be. I can learn, as well as do the legwork in gathering schematics, knowledge, and parts. From what very little electronic circuitry experience that I have had, I suspected a leaky/faulty capacitor, (possibly more than one) causing an "unbalanced" signal back to the relay. By the way, I had a Marantz that had almost identical symptoms, and it turned out to be one of the rail 10000uf 63v capacitors that was faulty. I am wondering if the problem with this unit might also be one or both of the the rail caps??? I am searching for a schematic for this unit, and hopefully will be able to have some idea what the problem is prior to asking one of my buddies to help. Thanks Mark |
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