Electronics > Repair

Yamaha digital piano produces no sound

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Hi All,
I have a used Clavinova CVP 209 that isn't playing any sound from the keys or memory, neither on headphones nor line out. The speakers work OK from line in, and the rest of the lights and screen seem to work just fine.

I have tried doing a factory reset by holding down the top key and turning it on, but that doesn't help. I did the RAM/ROM checks and they're OK. I checked the volume potentiometer and it seems OK (works with line in audio). I'm thinking it might be faulty DACs from the synth board (IC 28 and 29: https://elektrotanya.com/yamaha_cvp-207_cvp-209.pdf/download.html) or op amps. Not sure how to narrow it down more. I've scanned the boards for bad capacitors, but only found one that's slightly suspicious but on the mic input circuit which shouldn't affect anything anyway. Does anyone have experience with this? I don't have an oscilloscope so I can't do any precise voltage checks beyond multimeter checks.

check the DACs have their -5v supply, provided by regulator IC46.
Possibly the only bit of circuitry that uses this -5v voltage, haven't looked properly.

Also, what is the voltage on the outputs of the dual op-amp IC43? 
Measure this on R50 and R51, and check these resistors aren't open circuit.

If both DAC 5v supplies are present, and the op-amp voltages are zero, you could try running a cable from the working Aux in and speaker circuit, and touching the signal pin of this cable to R50 and R51 to see if there is any audio here.

If the op-amp outputs are DC, don't try this aux in connector, the circuit is faulty.

I'm not sure if I did the checks correctly, because these values I checked aren't making sense.

The DACs read 10v across the two outer pins (11 and 20). Is that because pin 20 is at -5v and 11 is at +5v? I also checked the voltages going to the 5v regulator and they all seem to be 12v as expected. I'd rule out power supply issues.

The voltage in DC from the opamp appears to be .09v on one channel and .19v on the other, but neither giving any sound when probed. When I check with the AC 200v mode I get no reading. That is while playing a diagnostic test pitch. I'm not sure what this means... good or bad?

Unfortunately I can't really get to the R50 and 51 because they're on the underside of the motherboard and I don't think I can disconnect all the cables while it's on to access it. The opamps are there too. But for what it's worth, I put a resistor in series with the audio probe, so in the off chance the resistors are bad, that impedance should be taken care of.

Any other ideas?  |O

Reading 10v at pins 11 and 20 shows the DAC power supplies are good.
Reading a low voltage on the op-amp outputs show the op amp is probably ok, they usually go fully DC supply voltage when failed.

Interesting question is why are both DACs apparently dead?

Is it possible one failed some time ago, was ignored/put up with/un noticed until the other died more recently leaving the piano totally mute?

The DACs have 4 datalines from the processor, DACL, DACR, WCLK, QCLK.  If either of the CLK signals are missing then both DACs won't work.
It's unlikely any of these signals are missing, but you could check continuity of the PCB traces from processor to DACs to confirm there isn't a broken trace.

To prove it is not the op-amp, you could just remove it, then you should still be able to probe the output of the DAC directly, the op-amp is just a buffer.

I mentioned probing those two resistors only because it should be much easier to do so than the IC pins themselves, where there is the added risk of shorting pins.
But clearly it isn't.

Ah, the DAC's are Current output devices, so you need a working op-amp.
(Edit:  They act as a current to voltage converter)

So to rule out the op-amp you should change it.


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