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Old 18th November 2005, 05:17 PM   #1
tmblack is offline tmblack  United Kingdom
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Default Yamaha CR-820 schematics?

I have this Yamaha receiver where the relay circuitry is acting up and not allowing the amplifier to function.

Anyone have the schematics of this?

Thanks

Tom
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Old 18th November 2005, 08:49 PM   #2
anatech is offline anatech  Canada
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Hi tmblack,
What's happening exactly? BTW, Yamaha loves to use lamps in muting and protection circuits. If there are any burnt out, replace them and your problem may go away.

Sorry, no longer have that manual.

-Chris
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Old 18th November 2005, 11:50 PM   #3
tmblack is offline tmblack  United Kingdom
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Sometimes the unit turns on after a very long wait and the relays make a click, then it might make a loud crack and the unit goes off again.

Maybe there is a leaky capacitor or dc offset?
Not a bad looking unit for the late 70's, I'd like to fix it.

Tom
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Old 19th November 2005, 01:11 AM   #4
anatech is offline anatech  Canada
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Hi Tom,
Sounds like an offset problem all right. It is a good rcvr.

If I'm not mistaken, that unit uses an STK voltage amp, doesn't it?

If so, I'll bet that's gone bad. You can try resoldering the pins first. Clean off the old solder and use flux.

-Chris
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Old 19th November 2005, 06:11 AM   #5
tmblack is offline tmblack  United Kingdom
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No, it actually uses all transistors in the amplifier.
Any idea how the relay circuit works?

Tom
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Old 19th November 2005, 07:28 AM   #6
dudu is offline dudu  Israel
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Default Yamaha cr-820

Hi
Go to www.stereo411.com/forum and ask Age for the
Yamaha CR-820 service manuals,
if he hasn't the schematics , write u'r e-mail address and i sent u the CR-1020 or CR-620D
Regards
Dudu
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Old 19th November 2005, 11:33 AM   #7
djk is offline djk
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Start by replacing the cap on the base of TR804, then the caps on the base of TR704, TR705 to ground.

There may be other problems.

http://www2.yamaha.co.jp/manual/pdf/...AFR/CR-820.pdf
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Old 19th November 2005, 06:16 PM   #8
anatech is offline anatech  Canada
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Hi djk,
Thanks for the link, I can almost make out the numbers.

Tom,
Look to see if there are bad solder joints. They will look frosty rather than smooth now, there may be a tiny black ring around the component lead. Remove the old solder, add flux and resolder. Don't use too much solder (avoid leaving solder blobs). Clean the PCB with lacquer thinner and look for solder wiskers when you are done. Replacing the electrolytic caps as djk suggested may improve the sound quality at this age.

-Chris
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Old 20th November 2005, 01:56 AM   #9
tmblack is offline tmblack  United Kingdom
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Wow,

thanks for the links guys.
I am very impressed!

Yes, I will replace those caps and look around the board.
Do relays usually need replacing after a couple od decades?

Tom
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Old 20th November 2005, 02:57 AM   #10
djk is offline djk
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It's not likely to be the relay.

The relay drive circuit has an RC time constant before it latches, that is the first cap I want you to replace. The drive circuit also senses DC and cuts the relay off. The second set of caps I listed can affect DC off-set.

As Chris pointed out, the loud noise when it cuts out is probably DC. The DC could be from many things. IIRC, TR713, TR714 run hot and the solder joints can go bad. It could take some time to actually find the problem.
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