Yamaha digital piano produces no sound

[Pianomancer]

Hi All,
I have a used Yamaha 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 ... nload.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.

[The Elf]

Local Off?

[James Perrett]

I've just repaired a Korg piano of a similar age where most of the surface mount capacitors had died. Interestingly, Yamaha use far fewer capacitors in this unit but that's where I'd be looking first.

However, you definitely need some diagnostic tools to trace the signal through and I would suggest a cheap oscilloscope (you can pick up low bandwidth ones on eBay for around £30) or maybe some kind of signal tracer. If you have an instrument input on your audio interface you could probably build a signal tracer probe - you would need a capacitor for DC isolation at least.

[BJG145]

I have tried doing a factory reset by holding down the top key and turning it on, but that doesn't help.

...did the screen confirm that the reset took place...? Are you able to check MIDI out and/or USB MIDI out by connecting them to a PC or sound module...?

[Pianomancer]

Yikes to all the dead capacitors, that doesn't sound fun... I'm hoping this isn't something I'll have to deal with. I don't have a tester, so I'm not stoked about having to desolder cap after cap to check them. Is there an easier way (with a multimeter)?
How would one jerry rig audio in to make an oscilliscope ? I guess I'd connect to my laptop running Audacity or something?

Local midi settings are reset to defaults after factory reset. The screen doesn't give an indication, but after changing a setting and then resetting I can see that the setting changed back so it must be working. I thought about midi output but would it help to know if it's working or not? It's a different part of the circuit so it wouldn't tell me much I think.

I read in another forum someone who was going to inject analog signal directly after the DACs which sounded like a good idea. Could I just take an audio cable playing music and touch it to the trace before+after the preamp?...

[forumuser931182]

Plugging another keyboard in via midi in ( or a computer via midi interface ) will let you test the sound module of the piano - perhaps the pianos keys aren’t getting data to its sound chip. Also connecting the midi out from the keyboard will confirm the keys are generating data.
You can try touching points on the pcb with a capacitor and lead going into any amplifier and speaker. Can you see the dac output on the circuit diagram. Try there for a start.
You can also try the reverse and feed a dignal into the piano.
Unfortunately the circuit will be quite complex and this kind of testing will be very rudimentary.

[James Perrett]

Don't go desoldering anything until you know what the fault is.

Injecting a signal is a perfectly valid way to trace faults. In years gone by you could buy signal injectors for not too much money but these seem to be no longer available. You could certainly use a normal audio source but it would be best to add something like a 220 ohm resistor in series with the signal to avoid damaging anything.

I prefer to trace the existing signal and find out where it stops which is why I suggested using an instrument input on an audio interface which will have a high input impedance and so won't load the circuit under test.

[Pianomancer]

I know that the keys are working because in order to do the factory reset I press the uppermost key while powering. Also to enter diagnostic mode. I know the sound module has some issue because even the internal demo music doesn't play. If I had a midi cable on hand I could easily knock that one out though.

You can try touching points on the pcb with a capacitor and lead going into any amplifier and speaker.
...
You can also try the reverse and feed a dignal into the piano.

I recently tried feeding the DAC out pin some music from my phone via audio jack. There was only a small crack, so I got a bit timid and stopped. Should this normally result in audible music? Is the DAC out even AC current like the music? Why would I use a capacitor versus a resistor, and what orientation would the cap have to be in? I will try again like this, and probe other areas too. (fingers crossed for no smoke)

an instrument input on an audio interface which will have a high input impedance and so won't load the circuit under test.

I'm not sure what you mean... could this be an audio cable from a laptop? I don't have any other real audio equipment. Also, headphones have some impedence so would I be able to simply probe with my headphones?

[resistorman]

If you're going this deep, buy basic equipment... a scope, multimeter with capacitance testing capabilities, soldering station. All this is unbelievably cheap these days, and you have an innate curiosity and DIY attitude that leads me to believe the piano isn't the last thing you'll be digging into

[Sam Spoons]

Or just take it to a decent tech, You could easily do serious damage to the piano poking about without knowing what you were doing (don't ask how I know ).

[James Perrett]

an instrument input on an audio interface which will have a high input impedance and so won't load the circuit under test.

I'm not sure what you mean... could this be an audio cable from a laptop? I don't have any other real audio equipment. Also, headphones have some impedence so would I be able to simply probe with my headphones?

It sounds like you don't really have enough electronics experience to tackle this repair. You can damage things (and yourself) by just poking around without knowing the basics. This is a fairly expensive keyboard which deserves to be fixed properly.

[Pianomancer]

If you're going this deep, buy basic equipment.

Yeah, I definitely would but I don't plan on being here too long and I'd just have to sell it or something afterwards.

I have asked around and techs won't touch this kind of board anymore. Yamaha doesn't sell these parts (20 years old) which obviously aren't built to last. I called out a local 'tech' and he ended up screwing it up more than before, and left without finishing the job so I'm kind of on my own here. I don't have lots of electronics experience which is why I'm here. I'm really just a pianist who wants to play again, as well as build my own down the road!

[James Perrett]

Where are you based? Maybe someone here would know someone good.

[resistorman]

If you're going this deep, buy basic equipment.

Yeah, I definitely would but I don't plan on being here too long and I'd just have to sell it or something afterwards.

I have asked around and techs won't touch this kind of board anymore. Yamaha doesn't sell these parts (20 years old) which obviously aren't built to last. I called out a local 'tech' and he ended up screwing it up more than before, and left without finishing the job so I'm kind of on my own here. I don't have lots of electronics experience which is why I'm here. I'm really just a pianist who wants to play again, as well as build my own down the road!

The equipment is very small these days, here's something that does it all: https://smile.amazon.com/Oscilloscope-M ... 414&sr=8-6

[Pianomancer]

Where are you based? Maybe someone here would know someone good.

I'm in Utah, and the Yamaha people said they don't sell the boards anymore to techs. Even so, a board would run hundreds of dollars and I'm averse to dumping that money into a 20-year-old piano. And in the back of my mind I know it's just one tiny part of the board that's bad and the rest is good, so I feel confident I should be able to find it and repurpose this thing.

The equipment is very small these days, here's something that does it all: https://smile.amazon.com/Oscilloscope-M ... 414&sr=8-6

I must say that thing looks awesome. I wonder how its capabilities stack up against a standalone osc unit. Then I wonder why I couldn't just make my own with my Raspberry pi that's lying around..... another project for another day!

I ended up injecting some audio into the two layers of opamp inputs and I got sound output, so that tells me they are working and the DACs must not be. If there's nothing I am missing here, then I'll be ordering a couple of these obsolete DACs and soldering them on like a surgeon in the coming weeks.

[jjlonbass]

I wouldn't jump to the conclusion that the fault lies with the DACs IC28 & IC29 just because the analogue circuitry that comes after them is working. I would first make sure that all of the power supply rails are present and correct, perhaps starting with the +/- 5V supplies +5A and -5A that only go to the 2 DACs.

It may well be a single component that has silenced the instrument, but unfortunately, it's more likely that there are a whole load of faulty electrolytic capacitors to replace.

It's your instrument, so it's up to you what you do with it, but it would be a shame to waste money buying components that you don't need when a methodical approach should find the cause of the fault.

John

[Pianomancer]

I wouldn't jump to the conclusion that the fault lies with the DACs IC28 & IC29 just because the analogue circuitry that comes after them is working. I would first make sure that all of the power supply rails are present and correct, perhaps starting with the +/- 5V supplies +5A and -5A that only go to the 2 DACs.

I checked this power and read 10v (I suppose because from -5v to +5v). From here I skipped over the DACs and checked the opamps on the other side, which seem to be working. If all of that output circuitry is OK, and I assume the main CPU to be OK, then the only conclusion I can come to is that the DAC in the middle isn't doing its job. What else could I be missing? I can't check every capcitor on the board, and this is the only one that looked potentially suspicious: https://pasteboard.co/FLdu26kpqYth.jpg

[James Perrett]

It is very unlikely that both DACs have gone bad at the same time. In fact it is very unlikely that the DACs are bad at all. If you are insistent on trying to fix this yourself then look at the things that are common to both DACs like the power supplies, clocking and data input. I would also be suspicious of any surface mount electrolytics associated with the DACs - these are much more likely to have failed. But be very careful desoldering them and ignore much of the information on Youtube - you'll end up ruining the board if you follow some of the videos on there.

You should also take a look at the data sheet for the DAC chip to see what you should expect to see on each pin and measure the signals on each pin to check that they really are as expected.

You may also have to get into looking at the digital input to the DAC and for this you will need a 'scope with a 20MHz bandwidth or higher. If you are serious about wanting to learn about electronics then it might be worth looking at the cheaper Picoscopes which use your computer for control and as a display.

[Pianomancer]

Because this unit is preowned (and 20 years old) I don't know the history and it could have slowly gone bad from stereo to mono and then finally out. I think it's possible it was tolerated in mono until it finally died. Anyway, I don't have an oscilloscope to check the data and clock lines, but I will try checking AC voltage with my multimeter and see if I get something. It appears to be .3v inputs.
https://pdf1.alldatasheet.com/datasheet ... 1702U.html

I don't know that there are any capacitors between the CPU and the DACs so I'm not sure what caps I'd need to check.

The picoscope is a good idea, to offload the monitoring and software to the laptop. I would probably go that route if I bought one, but not sure about the bandwidth though.

[jjlonbass]

The parts list for this instrument shows 83 electrolytic capacitors, any or all of which could be faulty - they may look normal but actually be faulty. The best way to test these is by using an ESR meter. These capacitors are mainly used for power supply rail decoupling, a faulty cap will result in a noisy supply rail which will cause whatever is powered from it to behave in an incorrect and unpredictable manner.

It's very tempting to think that there is not much between the CPU and the DACs, but this is untrue, between the CPU and DACs is most of the instrument including quite a few large, custom digital ICs.

You may be able to determine that the DAC data and / or clock inputs to the DACs are stuck high or low with your multimeter, but that's about it. The DACs have standard TTL level digital inputs i.e. 0.8V to 0V is a logic low, 2.4V to 5V is a logic high.

This is a complex system containing many surface mount components; it isn't really suitable for an inexperienced person to attempt to repair.

John

[Pianomancer]

Actually what I meant by CPU was the SWP30 IC. That turns out to be the wave processor.

I just tested the line in today and realized it isn't producing any sound, whereas aux in does. That's interesting because the line in goes through an ADC, through the CPU, and has to come back out the DACs where the aux in goes directly through opamps to the speakers. That seems to point again to faulty DACs...?

I'll see if I can get my hands on a cheap ESR meter. Unfortunately they take weeks/months to ship from China.

[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?

[jjlonbass]

An ESR meter is only useful for testing electrolytic capacitors - it's unlikely to tell you anything meaningful about ceramic capacitors, especially low value ones. Ceramic capacitors tend to be reliable, so I would concentrate on electrolytics first.
What ESR reading in ohms do you see for the electrolytics you removed and what are their voltage ratings and values in microfarads? If you've tested any of the 2200uF, 3300uF or 3900uF caps on the power supply board, you should see an ESR of less than 0.5 ohms.

Have you measured all of the power supply output voltages with respect to GND?
Please can you measure the voltage between AGND and +5A and -5A on the DM board. Then between 3.3D and DGND on the DM board.

The fact that the Mic / Line in doesn't work only shows that one or more stages between the input socket and the output are not working - it doesn't immediately point the finger at the DACs. The fact that aux in works shows that the +12A / -12A supplies are healthy enough for the op-amps on the A-JACK board to function.

John

[Pianomancer]

An ESR meter is only useful for testing electrolytic capacitors - it's unlikely to tell you anything meaningful about ceramic capacitors, especially low value ones. Ceramic capacitors tend to be reliable, so I would concentrate on electrolytics first.

Good to know. What I've found is a lot of bad electrolytic capacitors out of spec on the main board, so I'm going to be replacing them in the coming week(s). However, this cheap ESR meter really hasn't given me any actual ideal readings on capacitors, because I think there's some variance. I'm most worried about the caps that read 50ohms ESR. Also, it's strange that many 10mF caps on the board consistently read as 430mF - is there something to this?

Power supply caps were not far above spec so I think they're fine. Again, because lights and other functions seem to work I would think a bad cap there would show itself in more ways than one. Once I get everything back together with new caps I can check those voltages.

[Pianomancer]

I replaced all electrolytic caps on the main/synth boards, but nothing changed. The bigger caps on the power supply board seem to read higher than normal ESR, although I'm not sure how much to trust my meter. For example, I desoldered a 3900mF cap that should be .04ohm but it was .17. A 3300mF cap measured .19 instead of .04. But considering power appears to be reaching all parts of the board, do you think this would lead to no sound whatsoever?

I rechecked +5v -5v power to the DACs and it seems OK. Also, the 3.3v regulator is fine, but what I thought was supposed to be 5v from the 12pin cable measured 12v to ground. I guess power supplies are working OK.

I probed the DAC clock line with a capacitor and only got a small pop but no real sound. I'm afraid the speakers would be too much impedance to get a signal anyway. The input data line gives a sort of white noise, so at least there's something going there. Is there anything else I should check?