Yamaha CR-820 DC offset too high

djez

Active Member
The offset in both channels is about 75mV. I've recapped the power supply except for main filter caps, tone control board, and both amplifier channels. Almost all the capacitors were way out of tolerance or had extremely high ESR's. I replaced TR 701-704 with closely matched KSA992's. The bias is adjusted in both channels to 8mV. Any ideas would be greatly appreciated.
 
What are you reading for the + and - rails at the main caps? Precisely..
 
Does your DC offset drift 5-10mv?
I haven't been monitoring it along with the rails, but it has fluctuated between 70-100mV when I've checked it today. It's currently at 93mV and both channels seem to move together.
 
Hi, just came across this post and I have the same issue on my Yamaha CR820. DC offset showing around 70mV on all speaker output. Not sure where to begin in trying to fix this issue. Djez, did you manage to fix the issue please?
 
Hi, just came across this post and I have the same issue on my Yamaha CR820. DC offset showing around 70mV on all speaker output. Not sure where to begin in trying to fix this issue. Djez, did you manage to fix the issue please?
I put in gain-matched 2SA872’s in TR 701/703 & TR 702/704. It brought down the offset to 0 & 13mV. You could use thermal adhesive then shrink wrap the pairs to thermally couple, but I didn’t need to. I might end up doing it since it’s the best way IMO. I still need to sort out why my bias isn’t registering, but I think it’s pretty close, so not too worried about it. I have a 2nd 820 that was a donor unit, and I’m going to see if I can get it operational.
 
I put in gain-matched 2SA872’s in TR 701/703 & TR 702/704. It brought down the offset to 0 & 13mV. You could use thermal adhesive then shrink wrap the pairs to thermally couple, but I didn’t need to. I might end up doing it since it’s the best way IMO. I still need to sort out why my bias isn’t registering, but I think it’s pretty close, so not too worried about it. I have a 2nd 820 that was a donor unit, and I’m going to see if I can get it operational.
Thanks for the info. So you replaced transistors TR701/TR703/TR702/TR704, to bring down your DC offset.. Do you think I should do the same? Does setting the DC Bias to 8mV bring down the DC offset? Thanks
 
Thanks for the info. So you replaced transistors TR701/TR703/TR702/TR704, to bring down your DC offset.. Do you think I should do the same? Does setting the DC Bias to 8mV bring down the DC offset? Thanks
Offset isn’t affected much by bias. Without an offset potentiometer, it is set by matching the differential pair of transistors on each channel. Gain match them with a transistor tester as close as you can. Hopefully that’ll solve your problem.
 
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