Wrong power supply... Look at the (Muting & Power supply) circuit. Post a snippet of that schematic.
Yamaha C-80 lost sound switching inputs
- Thread starter ghankstef
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- preamp yamaha c-80
ok block diagrams are a good zoomed out view - will start looking at them too
If bench work sends me to a world of confusion or overthink...block diagrams bring me back to earth.
Recommend checking chassis ground screws on the boards for tightness, I think they're copper and strip easy IIRC.
Getting close
Recommend checking chassis ground screws on the boards for tightness, I think they're copper and strip easy IIRC.
Getting close
I'd also re-flow the IC309 pins...The far end of the de-soldered red/white wire.
Top and bottom covers off - on the bench I have a copper wire running from front and back of chasis to the middle piece with gator clips. Still will check
IMO it would be the perfect pre-amp if they didn't use f'ing plastic side panels. 
Great piece, just harder to shoot faults.
Great piece, just harder to shoot faults.
Sparkplug
Super Member
So they’re ±15V and in this case powering IC309 (op-amp) on tone control 2 (new continuous loudness), I guess. Worth checking IC309 supply pins (5 & 9) to make sure it’s working properly. If you measure anything other than ±15V, then the IC is bad. I had a similar thing on my C-6 a while back.
IC309 = NJM4558
The OEM 4558 is and SIP. Your selection is a DIP. Would need and adapter board.
Sparkplug
Super Member
Yes … I copied and pasted the first thing I found in Mouser, not sure if they have SIP as well or not. If not, an adapter will do the job.
Edit: This OEM 4558 is a 9-pin animal based on the C-80 schematic, whatever adapter used must be custom made. The ready made ones are usually for 8-pin normal ICs available today.
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Measure the power supply voltage at the emitters of those two transistors. Expect around + 15vdc & - 15vdc. This same supply voltages are used in a few other circuits as well. I doubt if these two pass transistors are the problem.
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Sparkplug
Super Member
The schematic shows those two emitters (Tr340e/341e) at ±15.6V. Am I missing something? Where do you see ±40V? You’re right, probably not the problem here.
My-bad...I was looking at a very poor-quality scan at the time of posting.
Unfortunately the IT Dept. where I work . Blocks downloads to my HiQ scans as well as HifiEngine.
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Sparkplug
Super Member
TR340 abd TR341 are 15.03 and -15.07 VDC at the emitters, That seems right on.
IC309 - now I'm not sure which side is pin 1 and which is pin 10. I can't tell from the schematic or the printed circuit board diagram so I'll try it both ways
With tone control board #2 installed in the unit assuming the bottom most pin is #1:
pin 5: 13.3 V
pin 9: 15.11 V
Assuming the top most pin is #1
pin 5: 13.1 VDC (same pin either way)
pin 9: 15.1 V.
Ok so I don't see a -15 anywhere. Hmm did I install the wire connecting to tone control board #2 the wrong way around?
IC309 - now I'm not sure which side is pin 1 and which is pin 10. I can't tell from the schematic or the printed circuit board diagram so I'll try it both ways
With tone control board #2 installed in the unit assuming the bottom most pin is #1:
pin 5: 13.3 V
pin 9: 15.11 V
Assuming the top most pin is #1
pin 5: 13.1 VDC (same pin either way)
pin 9: 15.1 V.
Ok so I don't see a -15 anywhere. Hmm did I install the wire connecting to tone control board #2 the wrong way around?
