Yamaha CR-2020 High Bias Left Channel.

[TubeJunkie]

Hello. I have a Yamaha CR-2020. Belongs to a good friend. He said it works for hours then goes in protect mode. Quickly found left channel had no bias voltage. . Didn’t find anything bad in the power supply, so I started investigating the amp boards. Left channel amp board: I found an open 68 ohm / 1 watt fuse resistor , replaced it with a 68 ohm/2 watt. Also found the 2sc458 faulty. TR608. This is part of the bias circuit. Replaced it with KSC1845. I think I may have put it in backwards? Left channel bias is now over 400 mvDC…when powered on with dim bulb tester. . The old 2sc458 is the Hitachi sloped top/ and flat on other side. The flat side should be E.C.B. Correct? I looked up pinouts, and double checked, but I’ve checked everything thing else. The boards aren’t marked ECB either. . . Anyone willing to give advice, I’m more than grateful. Thanks.

 

[mbz]

2sc458 is the Hitachi sloped top/ and flat on other side. The flat side should be E.C.B. Correct?

Nah, the flat face is the back, the smaller bevel face is the front ecb.

 

[avionic]

I found an open 68 ohm / 1 watt fuse resistor , replaced it with a 68 ohm/2 watt.

Well. It is no longer fusible. Like replacing a 1A fuse with a 2A fuse.

 

[kwayde]

 

[TubeJunkie]

Well. It is no longer fusible. Like replacing a 1A fuse with a 2A fuse.

You are correct sir. But that’s all I had for testing. The original resistor is marked HW-21468. Micron 77. Online search says it’s a 1/2 watt. Looks big to be a 1/2 watt. What’s your thoughts on a proper replacement?

 

[TubeJunkie]

Nah, the flat face is the back, the smaller bevel face is the front ecb.

I have proper bias now. I had T608 in backwards. Thank you all for pointing me in the right direction.

 

[TubeJunkie]

View attachment 3856092

Thanks so much for the pic and info! Big help!