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Yamaha CA-1010 Setting Idle Current (bias?)

SaturationPt

SaturationPt

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Hi all, great forum, have been lurking for about a year, ... was a reformed audiophile, past tech, EE, ... my son got me hooked on the hobby again and I have a small stash of vintage so:

I have a Yamaha CA-1010 that I decided to start using, needed to replace the protection relay and set the "idle current" per the FSM. Relay replacement went great, setting L channel went great (25mV Normal, 280mV A-Class).

R channel not so good. Set Normal to 25mV via VR301, switched to A-Class and voltage was 25mV. Turned VR302 until 280mV, ... back to Normal setting and at 280mV. Adjust VR301 to 25mV and switch to A-Class: 25mV again.

1st question:
It is my assumption at this point that the Class-A / Normal relay (same Panasonic as protection relay, thanks Yamaha for keeping it simple). I have one in-bound. Does this sound likely to those better acquainted with the CA-1010?

2nd question: I have adjusted VR302 (R-Channel) to mid-point (since the pots are interactive at this point) and then adjusted VR301 to 25mV in Normal mode, and am using the amp. Does this sound safe? DC offsets are <10mV IIRC. I'd like to continue using it until I get the part and time to install it.

Thanks again!
 
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Measure the collector voltage of your output transistors in normal mode. Then in class A. In class A . If the mode relay is properly working the collector voltage should drop in class A.
 
Class A rail approx. + & - 22 vdc
Class AB (normal) rail approx. + & - 55 vdc
 
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Actually if the normal/class A relay was the problem. It would foul up both channels.All the relay does is switch power transformer secondary taps.
 
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TR311 and/or TR312 on the R-channel may have issues. Or cold solder connections.
 
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SaturationPt said:
2nd question: I have adjusted VR302 (R-Channel) to mid-point (since the pots are interactive at this point) and then adjusted VR301 to 25mV in Normal mode, and am using the amp. Does this sound safe? DC offsets are <10mV IIRC. I'd like to continue using it until I get the part and time to install it.
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As long as its stuck in normal 25mv. It shouldn't be and issue.
 
Thanks Avionic.
I'll continue using in normal/25mV for now, am rehabbing an SA-9900 that I can use in its place while I go through it more thoroughly. The reminder that the relay only changes power is a good catch for certain.

I'll look at TR311 & TR312 and the solder joints, it would be nice to find it that easily.

It's my favorite sounding amp, not a powerhouse but as nice as it sounds after all of these years I think I probably should give it some serious attention.
 
CA-1010 is a damn nice amplifier . My brother bought one and a pair of NS-1000M's new at German BX. I ended up with both the NS-1000M's and the amplifier. " Thanks Bro !":naughty:
 
Super clean CA-1010, needed some basic maintenance, controls cleaned, lamps replaced, amp adjustment.

How critical is it to have an 8 ohm dummy load attached when setting idle? Before adjustments, the readings were: Normal - L ch 18 mV, R ch 7 mV. Class A - L ch 115 mV, R ch 88 mV.

Volume turned down, no signal, coupler off. I left a pair of 8 ohm speakers hooked up. Both Normal and Class A adjusted easily to spec. Seems to throw off a fair amount of heat, though.

Q1: Is it normal for the original readings be that far off? It's probably never been adjusted before.

Q2: Is this amp known for running fairly warm?
 
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