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Old 17th June 2015, 11:40 AM   #1
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Default Yamaha CA-610ii

Hi,

This amp had no sound on both channels when I received it. The protection relay was not turning ON. I opened up the amp and realised that a few resistors and 2 transistors have blown. I replaced them and turn the amp ON. There was one 1S 1555 diode blown and I replaced it with a 1N 4148. It was still the same. The relay is not turning ON. I checked the transformer and noted that the 27V AC winding has no voltage. I added a small 24V AC transformer in its place. The relay is still not turning ON and no sound. Then I tried bypassing the relay and connected the speakers to the direct output from the power transistors (prior to the relay). There is sound on both speakers and the amp seems to work as normal. I have checked all resistors, transistors and diodes on the preamp and power amp board and they all seem OK. What can be the reason for the relay not turning ON.

Thanks

Carlos
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Old 17th June 2015, 01:17 PM   #2
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24 might not be enough
relay might be open
270R resistor might open under voltage
TR577--578 alike

But most of all try first with proper supply
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Old 17th June 2015, 02:58 PM   #3
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Notice one thing more

Often there small amount of offset in the output of the amplifier enough to trigger the protection but not enough to notice when listening check that also

Yamaha of that era could have some diff semis that are busted ...

Kind regards
Sakis
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Old 18th June 2015, 03:17 AM   #4
anatech is offline anatech  Canada
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Hi Carlos,
Open capacitors in that circuit can prevent the relay from timing out and coming on. The smaller ones seem to dry out quicker. Look at your DC lines with an oscilloscope to make sure you have steady DC voltage, not pulsating DC.

The transistors can occasionally open base to emitter. This is more rare. Of course, measure the amount of DC offset you have on each output channel.

-Chris
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Old 18th June 2015, 04:17 AM   #5
frangus is offline frangus  Australia
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I just fixed mine that had the same problem,

Replaced the smaller electrolytic caps on the main circuit as already suggested

Works fine now.
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Old 18th June 2015, 11:31 AM   #6
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Quote:
Originally Posted by frangus View Post
I just fixed mine that had the same problem,

Replaced the smaller electrolytic caps on the main circuit as already suggested

Works fine now.

Thanks Guys. It was a small electrolytic cap situated near the relay. The relay is working fine now.

Carlos
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