Yamaha digital piano produces no sound

[Pianomancer]

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.

[Audiorepair]

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.

[Pianomancer]

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? 

[Audiorepair]

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.

[Audiorepair]

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.

[Pianomancer]

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.

That's very possible. I think one of the channels is L+R combined, so if the other failed first it would be hard to tell the audio dropped from stereo to mono. I'm banking on that being what happened!
The traces don't seem to be bad but I can't really tell because they're so tiny and they go through to the other side. I have to believe the CPU is giving clock signal OK.

I tried injecting some audio into the opamps input (there are two sets) and I got sound, sometimes with a fright... so that tells me the weak link here is the DACs. I have to say trying to only touch the right pin on the SMD chips was pretty nerve-wracking but I mostly touched the right ones. It gave me some feedback when I didn't.

What do you mean by converting current into voltage? Is that shorthand for saying voltage stepping?

[Audiorepair]

What do you mean by converting current into voltage? Is that shorthand for saying voltage stepping?

pg 6 explains this.

https://www.analog.com/media/en/training-seminars/tutorials/MT-019.pdf

[Audiorepair]

I tried injecting some audio into the opamps input (there are two sets) and I got sound, sometimes with a fright... so that tells me the weak link here is the DACs.

Yes, sadly it is looking like a problem before the op amps.

If you can't scope the datelines because you don't have a scope, then the only other option is to try and replace one DAC.

Though you could monitor the datalines with an AC voltmeter, while turning the test tone on and off.
This may show a difference on the DACL and DACR lines, which you could possibly use to guess whether the Clock signals are present or not.



Edit:  Or even metering DC.  You are just looking for changes.

[Decapitator]

Static DC voltage checks will take you just so far. At this point, I'd strongly suggest picking up an oscilloscope. It doesn't need to be anything fancy with all the latest bells and whistles. A used 20 MHz dual channel analog scope made within the last 40 years or so will help you pinpoint the issue. Check Craigslist, Ebay, or other local sources. You should be able to find something suitable in the $20 (local) to $100 (shipped) range with probes.

[Audiorepair]

20 MHz PC based scopes are quite cheap too.

https://www.amazon.co.uk/Hantek-Digital-Storage-Oscilloscope-PC-Based/dp/B015XTOOKY/ref=sr_1_6?keywords=USB+Oscilloscope&qid=1648288164&sr=8-6

[Pianomancer]

pg 6 explains this.

https://www.analog.com/media/en/training-seminars/tutorials/MT-019.pdf

This took me a while to get... after reading about the terminology, I think it's confusing to say 'converting from current to voltage'. Isn't it just that the signal varying in current from the DAC is translated into a signal varying in voltage from the opamps?

This also makes me wonder why I was getting sound at all when I injected audio into the opamp input. The audio signal would be a voltage signal, and the opamp is expecting a current signal, correct? I'm still adrift out at sea with all of this.

I will try to monitor the DAC clock/data inputs as best I can with a multimeter for now. Thanks a lot for the suggestions.

[james_s]

Static DC voltage checks will take you just so far. At this point, I'd strongly suggest picking up an oscilloscope. It doesn't need to be anything fancy with all the latest bells and whistles. A used 20 MHz dual channel analog scope made within the last 40 years or so will help you pinpoint the issue. Check Craigslist, Ebay, or other local sources. You should be able to find something suitable in the $20 (local) to $100 (shipped) range with probes.

Even one of those little Chinese pocket size toy scopes ought to work for checking for activity on the DACs, a logic probe could give you some clues too. If the DACs have a clock or enable don't forget to check that too.

[cncjerry]

Can you test the midi output if it has one?  That will tell a lot.

[Pianomancer]

I checked the data and clock ins of the DAC and couldn't detect any signal from my multimeter AC or DC. Is it possible there's no signal, or it's just so fast and minute it isn't being picked up by the multimeter?

I noticed also that 'line in' isn't producing sound (whereas 'aux in' does). That's interesting because it goes back through ADCs, to the CPU, then back out the DACs whereas aux in just bypasses and goes to the speakers. Could this help pinpoint the DACs as the issue?

I'm looking into ESR meters so I can check the caps for sure.

[james_s]

It's fairly apparent that the DACs aren't working, but why is unknown. It could be a problem with the DACs but it's just as likely I think that they're not receiving any data to convert. Unfortunately without a scope or even a logic probe or something else with a MIDI interface to connect it to you are kinda flying blind.

[cncjerry]

You need to determine if it is the key generating circuitry or the audio.  If you get midi output then that is half the battle.  You can pickup a midi interface from local retailers.  You can then test the keyboard and also send it notes from a PC.  Both windows and macs have midi trace programs. 

I assume you have the manual for it.  Many keyboards can turn off local mode where all they do is send midi and make no sound at all.

[Audiorepair]

The OP haas stated there is no sound from keys or memory (presumably meaning sequences/songs etc)

They also state they are currently testing using a diagnostic test tone, presumably from Test Mode, thus bypassing the keyframe/MIDI etc.
Checking for the presence of MIDI on the MIDI output would though show that the keyframe is working, and could then also be used as a test tool.
You could achieve this by simply inserting a LED into the MIDI socket pins either side of centre and watch it flash with key presses.  (it would only work when inserted the right way round of course)


Trying a multimeter to see if even the tiniest bit of data/distortion can get through and display anything does not work, it seems, so without an oscilloscope there is not much more that can be done.


I would still change the op-amp IC, just to prove it is definitely not the culprit, as this has not been reliably determined yet.

[Pianomancer]

I've purchased a cheap Chinese ESR meter and checked through some of the big electrolytic capacitors on the power supply board. Despite getting higher ESR readings than expected on circuit, I desoldered a few of them and found the values to be within a reasonable range, although still a little high. Some capacitors don't read properly, such as the tiny ceramic caps on the synth processing board. They read anywhere from 0-35 picoferads or just as diodes for some reason. Anyway I don't think I suspect the caps at this point. Anyone have experience using these ESR meters? How much does the probes resistance affect ESR readings?

Checking the midi out with an LED might work, once I get all the pieces of the keyboard back together. But I won't be surprised that it probably is working ok.

I would still change the op-amp IC, just to prove it is definitely not the culprit, as this has not been reliably determined yet.

Which opamp? I ran aux in through the speakers fine, which employs the speaker opamps. And I injected audio right after the DACs which played ok as well. I don't suspect the opamps, unless there's still something I'm missing.

[james_s]

For what it's worth, ceramic capacitors almost never fail, ESR meters are only useful for electrolytic capacitors. Probe resistance should be compensated for, either way it's not going to be more than a fraction of an ohm in most cases. A capacitor would have to be *really* bad to get no audio.

Is there activity on the data bus into the DACs?

[Audiorepair]

I would still change the op-amp IC, just to prove it is definitely not the culprit, as this has not been reliably determined yet.

Which opamp? I ran aux in through the speakers fine, which employs the speaker opamps. And I injected audio right after the DACs which played ok as well. I don't suspect the opamps, unless there's still something I'm missing.

The op-amps and DACs work together to convert the current output DAC to a voltage output to the rest of the system.
If you look at the circuit, and remove the op-amps altogether, you could still pass through a signal connected to the DAC outputs via R54 and R55.
So this is not a test of the op-amps working properly with the DACs.

I said before it is unlikely the op-amps are faulty, as they usually go full DC supply voltage, but this is not a certainty.
If you want to prove beyond all doubt the op-amps are not faulty you will have to change them.

[james_s]

I still think it's worth looking at the inputs to the DACs before bothering to replace the op-amps or anything else. It's a serial interface so not as easy to test as parallel but you should have some activity on both the data and clock. In a pinch you might try connecting an amplified speaker via a resistor and probe both of those, you should hear awful digital sounding screachy noise.

[Audiorepair]

I still think it's worth looking at the inputs to the DACs before bothering to replace the op-amps or anything else. It's a serial interface so not as easy to test as parallel but you should have some activity on both the data and clock. In a pinch you might try connecting an amplified speaker via a resistor and probe both of those, you should hear awful digital sounding screachy noise.

Yes, but the problem is if these data signals are not present, the piano is unfixable.

The only way of saving this, I think, is to replace the op-amps or DAC's, or both, otherwise it is goodnight.

[james_s]

Yes, but the problem is if these data signals are not present, the piano is unfixable.

The only way of saving this, I think, is to replace the op-amps or DAC's, or both, otherwise it is goodnight.

All the more reason to check those signals before replacing parts. If there is no data going into the DACs then there is no sense in replacing op amps.

[Audiorepair]

Yes, but the problem is if these data signals are not present, the piano is unfixable.

The only way of saving this, I think, is to replace the op-amps or DAC's, or both, otherwise it is goodnight.

All the more reason to check those signals before replacing parts. If there is no data going into the DACs then there is no sense in replacing op amps.

Yes, but the OP is unable to test for digital signals, that has been established.

Only option they have now is to replace the parts.

[james_s]

I offered an easy way to check for presence of digital signals, just use an audio amplifier to listen to them. It's not nearly as good as a scope but it will tell you if there is any activity.