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Yamaha CR-600 Problem with Main Amp Test points

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Dennis Ondik

New Member
I am retire person who likes to fix things. I am trying to learn how to repair vintage receivers now (if i can find one at a reasonable price.) but that is not why I am creating this thread.
I am working on a Yamaha CR-600. I downloaded the service manual. Seems to be a problem with the main amp board. I checked the voltage between TP3 and TP5. It shows 30V. Should be close to zero. Trying to figure out what is shorted out and where. Any one have experience or can look at the schematic and make a suggestion. I hate to just go through willy-nilly and pull all the components and test them individually. I would like to find a few candidates to start with first. Please any help would greatly be appreciated.
 
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First things first:
1. Does the protection relay switches (do you hear a click) after switching the amplifier on?
2. Check the fuses F801, F802, F803 and F804
3. If the amplifier switches on, is there Direct Current (DC) on the speaker outputs (Check A & B)

On YouTube, there is a plethora of knowledge about vintage audio repair.
I can advise you to go to XrayTonyb https://www.youtube.com/@xraytonyb.
I have learned a lot from him.
 
EifX said:
First things first:
1. Does the protection relay switches (do you hear a click) after switching the amplifier on?
2. Check the fuses F801, F802, F803 and F804
3. If the amplifier switches on, is there Direct Current (DC) on the speaker outputs (Check A & B)

On YouTube, there is a plethora of knowledge about vintage audio repair.
I can advise you to go to XrayTonyb https://www.youtube.com/@xraytonyb.
I have learned a lot from him.
Click to expand...

The relay does not click on. I do have both + and - 12V and + and - 33V power to the board.
Fuses are OK. I checked them on the power board.
Not sure about the speaker output. I suspect that if the relay did not click on then there would be no DC to the speakers. (could be wrong but never checked)
 
Could very well be a shorted output transistor TR713 . I would check both TR713 and 715 out of circuit.
 
If TR713 was shorted E-C . That would put your 33v positive rail on the output of the left channel ( TP 3 ). If TR713 is not shorted then something upstream in the left channel is holding TR713 at rail.
 
Update... Checked almost all of the transistors and they showed OK with my Peak DCA55, Diodes seem to be OK . too. But I did find a bad Fuse Resistor. 100 ohm 1/2P. It was Open. Not sure how this would cause a high voltage from tp3 to TP5.
 
Have a look at C723 100µf/50v if it was shorted it would take out that fusible. That fusible being open would likely cause the hi voltage at the output.
 
Late to the party, but in addition to avionic's usual sound advice, I think it's also possible that the fusible resistor simply failed with age. They're kind of notorious for doing that. It probably makes sense to check the equivalent part in the other channel, too, to see if it has drifted high in resistance vaue.
 
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