Yamaha R-900 Receiver Protective circuit relay question

[[email protected]]

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

 

[Bob Parker]

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

 

[west]

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

 

[Carroll Conklin]

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

 

[[email protected]]

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

 

[Mark D. Zacharias]

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

 

[[email protected]]

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