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Yamaha B-1 trouble shooting needed

jefferylhenr

jefferylhenr

AK Subscriber
Subscriber
I am attempting to bring a B-1 back to life. Totally unknown history except it came out of an estate sale. One cell of the power filters were open. Replaced those and the rectifiers and have gone through all of the boards. No parts tested bad, all fuses were intact. All voltages confirmed through confirmation steps 2-6. On 2-6 I get good 15 volts and direct adjustment control with no issues. However, on 2-7 I am getting 47 volts?

What is that all about? Thoughts?
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Other than right channel rectifier which appears to have been changed when I first got the unit, everything was original. All the fets pass a diode test. 1732293372296.jpeg
 
Here are some relevant diagrams for reference. I am getting the same reading for step 2-7 on both boards
 

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Don't know the amp...
Might be helpful to measure Vdc a1 to GND then a3 to GND, repeat on other channel.
 
jefferylhenr said:
I will get all 100 or so pounds back on the bench in the morning and measure these voltages.
Click to expand...
Just for fun, first see if doing step 2-7 like this works.

1732350474888.png
Take note that since VR502 is the "master" bias control, it might take some minor readjusting of step 2-6 to dial things in as specified ...
 
Last edited:
I measured 518 again
-41.5 / -41.8 / -40.6
-41.43 / -41.73 / -40.72
514
-8.6 / -60.01 / - 60.05
-9.01 / -60.03 / -64.7
 
I also measured 512 and 513 get identical d,s,g on both sides. I am going to replace the 4.7 and 22k trim pots with Bourns 4 turn 500 mw 4 turn

3339W-1 and try it again
 
jefferylhenr said:
I also measured 512 and 513 get identical d,s,g on both sides. I am going to replace the 4.7 and 22k trim pots with Bourns 4 turn 500 mw 4 turn

3339W-1 and try it again
Click to expand...
Identical to what? each other or TR 518 and 514 ?

Can you display what they were ?

Athansios
 
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