EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Pianomancer on March 23, 2022, 07:23:26 am
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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.
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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.
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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
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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.
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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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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?
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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 (https://www.analog.com/media/en/training-seminars/tutorials/MT-019.pdf)
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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.
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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.
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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 (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)
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pg 6 explains this.
https://www.analog.com/media/en/training-seminars/tutorials/MT-019.pdf (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. :scared:
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.
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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.
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Can you test the midi output if it has one? That will tell a lot.
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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.
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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.
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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.
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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.
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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.
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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?
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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.
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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.
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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.
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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.
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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.
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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.
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Good idea !
But do not forget to place a cap in the input line
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So this is not a test of the op-amps working properly with the DACs.
I'm still not sure why my testing didn't cover that. Do you mean because my audio injection signal is a voltage signal already, that the opamps' IV conversion abilities are not being put to the test?
I suppose I could try to 'listen' to the data/clock lines of the DACs with its own aux in line, assuming it's going to be in the audible range. BTW what size capacitor would be recommended for probing this? I have an uneasy feeling about more such poking around though... I'll save that until I've replaced bad caps.
Speaking of which, I've found almost all of the electrolytic caps on the main board to be out of spec, so I'm going to be ordering a big box of new ones and soldering them on. If that doesn't do anything then I'll turn my attention back to the DACs. That being said, I haven't actually tested a single capacitor including my own that were actually within ideal spec, so I'm assuming there's a bit of range of tolerance with this cheap ESR meter. Also, the Arduino wire probes I'm using with it do introduce some resistance, so I'm not expecting perfect readings, just within common sense tolerance I suppose.
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I suppose I could try to 'listen' to the data/clock lines of the DACs with its own aux in line, assuming it's going to be in the audible range. BTW what size capacitor would be recommended for probing this? I have an uneasy feeling about more such poking around though... I'll save that until I've replaced bad caps.
Speaking of which, I've found almost all of the electrolytic caps on the main board to be out of spec, so I'm going to be ordering a big box of new ones and soldering them on. If that doesn't do anything then I'll turn my attention back to the DACs. That being said, I haven't actually tested a single capacitor including my own that were actually within ideal spec, so I'm assuming there's a bit of range of tolerance with this cheap ESR meter. Also, the Arduino wire probes I'm using with it do introduce some resistance, so I'm not expecting perfect readings, just within common sense tolerance I suppose.
It doesn't matter, it's just for blocking DC, anything from 1uF to 100uF or so ought to be fine, I usually don't even bother and just use a cheap amplified speaker to do stuff like that, I've done it many times.
I would be absolutely shocked if a capacitor that is out of spec would cause the symptom of no audio. I can't even really see how this could happen unless it was a coupling capacitor that had gone completely open. The very first thing I would do is check the digital signals into the DACs, that's such a trivially easy thing and can tell you so much so quickly.
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I've now resoldered all the electrolytic caps on the main/synth boards, and nothing changed.
So I rechecked +5v -5v power to the DACs and it seems OK. I probed the DAC clock line (with a capacitor) and only got a small pop but no real sound. The data line gives a sort of white noise, so at least there's something going there. Before I decide to order some DACs is there anything else I should check?
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The clock will be running at some MHz frequency so unlikely to be audible. Data will have a wide range of frequencies so broadband noise is correct.
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You could try turning the test tone on and off, or play the piano or have the piano play a song/demo whilst listening to the white noise.
If it changes in tone corresponding to data being played vs not being played, that would be a pretty fair indication that is is actually outputting valid data.
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I tried measuring the DAC clock line with the multimeter and surprisingly got 3v. And the test tones from R and L resulted in data signal from the L DAC and R DAC respectively. So I know there's SOMETHING going into the DACs and NOTHING going out. Doesn't that narrow it down pretty definitively? The only issue is I can't prove the DACs while the secondary synth board is on, because it covers the chip. So I won't know fully what's going on when working normally with both boards connected.
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I tried measuring the DAC clock line with the multimeter and surprisingly got 3v. And the test tones from R and L resulted in data signal from the L DAC and R DAC respectively. So I know there's SOMETHING going into the DACs and NOTHING going out. Doesn't that narrow it down pretty definitively? The only issue is I can't prove the DACs while the secondary synth board is on, because it covers the chip. So I won't know fully what's going on when working normally with both boards connected.
It's quite possible that LDAC and RDAC will always have a datastreem, regardless of whether the piano is playing any data. It will just be a stream of zero until something gets played, then will change in relation to the data.
So it is a CHANGE in the DAC signals you are looking for that will indicate whether or not the piano is outputting any data other than a stream of zeros.
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if you invested some $ in an esr meter, I think you could also invest some other $ in this :
https://www.aliexpress.com/item/4000071366189.html (https://www.aliexpress.com/item/4000071366189.html)
more than enough to detect signal presence, for audio stuff. a really handy device.
I have one, and often please to use it to check quickly for signals
although I also have 4 other "real" scopes on the bench.
edit: the scope you receive is the one with pictures in the body of the offer, not the one on the top with picture gallery.
edit2: you should also buy a scope probe with it, the crocodile clips that are with the scope are useless to trace signals.
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I agree that you should be using a scope to debug this problem.
If you're willing to pay a little more money I'd look at the Hantek 6022BE - currently available for around $70 from Amazon.
It's a USB scope so it needs a computer but you can also use an Android device -- perhaps even a phone or tablet:
https://rudysmodelrailway.wordpress.com/2019/09/13/hantek-6022be-usb-oscilloscope-and-6-scope-software-apps-to-go-with-it/
Hantek 6022BE Overview of Six Software Apps with Download Links
https://youtu.be/UgXfuQnupXg
And there's been a lot of discussion on the device on these forums.
The only caveat, especially for those new to using oscilloscopes, is the grounding issue. However, if your computer/phone/tablet is running on batteries and has nothing but the Hantek connected to it (i.e. no audio or other USB devices) you should be ok.
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So it is a CHANGE in the DAC signals you are looking for that will indicate whether or not the piano is outputting any data other than a stream of zeros.
Well that's what I meant, when I do the test tones there is some signal but not without. And I believe even sending potentially corrupted data should somehow be interpreted into some audible noise by the DACs, but alas.
The problem is I don't really have a lot of time here and can't wait on ordering new gadgets and things. These obsolete DACs will take a few weeks alone to arrive because they only seem to be available from Chinese stocks.
Edit: I should also say that even if I scoped something wrong with the signal coming from the synth gen, I don't think I would be able to do anything about it anyway. Signal comes directly from the synth IC which I have no control of. I'm looking for anything I could potentially fix.
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So it is a CHANGE in the DAC signals you are looking for that will indicate whether or not the piano is outputting any data other than a stream of zeros.
Well that's what I meant, when I do the test tones there is some signal but not without. And I believe even sending potentially corrupted data should somehow be interpreted into some audible noise by the DACs, but alas.
The problem is I don't really have a lot of time here and can't wait on ordering new gadgets and things. These obsolete DACs will take a few weeks alone to arrive because they only seem to be available from Chinese stocks.
OK then, so it does look like the CPU is sending data to the DACs when you turn on a test tone.
And also looks like the clock signal is present if you can meter something on that line, which will be constant.
So it is increasingly pointing towards the DACs.
With still a feint chance its the op-amps, but very feint.
The DACs you are buying from China are unlikely to be the original parts they may claim to be, though they may work.
So worth a punt, as your options are somewhat limited.
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Oh, actually I think you said you didn't hear anything on the clock line, so inconclusive, this signal may be orders of magnitude in frequency above the DAC signals.
If there actually is no clock then this is something that almost certainly can't be fixed.
Taking a punt on a couple of Chinese DACs is still pretty much your only option here.
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Check DC voltage on the clock line. If there's a clock, it will be about half the supply voltage. Then if you really want to make sure there's high frequency AC, connect a 1N4148 or similar diode in series with the multimeter, now the capacitance will charge up to close to the supply voltage minus a diode drop.
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Well I've finally ordered a couple DACs, definitely not Yamaha standard parts but even if just one of them works I should be in business. I'll keep my fingers crossed...
Yeah the clock was inaudible, but 3v so I guess it was either super high frequency or I messed up my probing somehow. Why would it be AC? If it's DC acting as a PWM signal would that imply the signal is more like 5-6v? Either way, it's not 0 and there's nothing more I can do.
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Anything that is a rapidly cycling voltage is usually considered AC, in the case of the clock it will be a roughly 3.3V square wave.
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But AC is typically (always?) a reversing of polarity, but the clock signal most probably stays within 0-3v. What would be the advantage of having an AC clock? Furthermore coming from an IC on DC voltage, that would mean it would have to have a DC-AC inverter.
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That's all a matter of perspective, as in whatever you consider "ground". If you apply a negative DC offset to that clock signal then it is now going above and below ground, ie it is reversing polarity. A clock signal is alternating between low and high, it is alternating current. Typically it isn't going below ground but that doesn't really change anything.
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But AC is typically (always?) a reversing of polarity, but the clock signal most probably stays within 0-3v. What would be the advantage of having an AC clock? Furthermore coming from an IC on DC voltage, that would mean it would have to have a DC-AC inverter.
It's a signal with AC and a DC offset if you like. A clock line going between GND and Vcc would have an average value in between and that's what the meter would read.
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Most multimeters have an AC frequency limit of 1kHz or thereabouts, they will not measure a high frequency clock signal meaningfully as an AC or DC voltage.
However, it may be possible to measure SOMETHING using such a meter, to guess whether a high frequency signal is present or not.
I suggested this very thing right at the start of this thread, in post no. 8.
I have just done a quick check, and my Fluke 177 has an AC frequency cutoff around 1kHz, though if I connect it to an 5v pk-pk 8Mhz signal generator, it displays 20mV DC, and 0v with the generator off.
It shows 0.4mV AC with the generator off, and 0.8v AC 0.8mV AC with the 5v 8Mhz signal, so clearly the AC range has noise issues, and doesn't really work.
So, I think the 20mV DC measurement could possibly be used to determine the presence of a clock, but that would kind of be a guess, really.
In the case of the DACL and DACR serial datastreams, such a meter might show an obvious difference between a datastream of no sound, a series of zeros, and the piano playing sounds, with the datastream now changed.
Which I think could well be a viable indication of a valid datastream.
Edit: Just tried the DC again, and a 5v square wave reads 114mV DC up to about 500kHz, and then tails off from there with increasing frequency, now reading 72mV at 8MHz, which is odd, as it was 20mV before.
Probably an error on my part, but the principle is still demonstrable.
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Ah, I just realised that my frequency generator is hooked up to my workbench via a 1:1 audio transformer and an XLR socket to test balanced audio equipment.
So my quick and dirty test had the inductance of the transformer across the generator output, which may have affected the readings.
I had the meter connected to the generator directly, not the XLR socket.
I'm sure every multimeter is going to behave differently, perhaps some won't work at all doing this.
But once you'd drawn a rough DC/frequency response you could actually have a rudimentary clock tester that would even show you the approximate frequency.
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But AC is typically (always?) a reversing of polarity, but the clock signal most probably stays within 0-3v. What would be the advantage of having an AC clock? Furthermore coming from an IC on DC voltage, that would mean it would have to have a DC-AC inverter.
Consider it an AC signal riding on top of a DC offset. Putting a capacitor in series with your signal tracer would block this DC giving you an AC signal.
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I see, so AC just refers to the fact that it oscillates with a constant rate. Bits turning on an off on a channel is considered DC because it's not regular and predictable?
So I finally soldered on two new Chinese DACs and there wasn't any audible feedback from the speakers.... however, I'm now getting quiet distorted but correct pitch notes from the headphones. So that's something. The DAC power pins are only reading around 1v now though, so I'll have to recheck my soldering on the tiny SMD pins and from the power supply. Not sure what has happened! The clk pin appears to be reading .3v so that means something must be working there.
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That suggests that the original DACs were the problem and that in the process of replacing them you have either caused a short somewhere, or installed counterfeit parts that have the wrong pinout or are the wrong part entirely.
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I measured the 5v regulator and it's putting out only 1.2v, yet the 3.3v regulator is getting 5v input just fine. I don't understand what happened, as I didn't change anything else on the board. How could a faulty DAC be affecting the regulator output voltage like that?
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loading the supply line?
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Unfortunately, buying cheap unknown parts just introduces more unknowns into the unknown unknowns.
Welcome to the real world.
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Try removing the new DACs and see if the supply voltage bounces back. Are these through-hole parts? Is it possible you ripped out the through-hole plating on one of the power pins?
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I know the old DACs were getting 5v, and now it's 1v. I resoldered/checked the connections but still am getting just distorted quiet sound. They are SMD so it's a pain to remove the chips entirely especially with the limited equipment I have, so maybe I should just desolder the 5v supply on one of them to check one at a time? Is it possible one of them is bad and bringing the other down with it?
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Here's the sound
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My guess is the DACs you got are counterfeit, some other IC that has the wrong pinout and just happens to be able to output something recognizable. I worked on an arcade board once and was surprised to find that just connecting an amplified test speaker to the digital line into the DAC resulted in badly distorted but recognizable audio.
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Well that's disappointing if that's the case, especially that both of them would be duds. So I have to believe if I had ordered different ones it would be a done job. I'm done testing though, as I have run out of time for this project. Thanks a bunch to everyone for your help and encouragement. It's hard to go at such a project alone!
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Where did you buy them? A large amount of the harder to find parts available from Chinese ebay sellers are counterfeit, they'll take whatever junk IC they have a lot of in the right package and relabel it as something more valuable. I don't see why you'd set it aside now, it sounds like you've solved the puzzle, the problem is bad DACs, and all you have to do is acquire a couple of the correct replacement parts and install them and you're done.
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I got them from a Chinese seller on ebay... not the most reputable source, but these chips are a little hard to come by and not as cheap as they ought to be. The problem is ordering new ones requires more weeks of waiting, and there's no guarantee the new ones would be good either. It's just time I don't have now. At least it's good experience to have going forward if I ever tackle such a project again.
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Well get the new ones from a reputable source, even if they cost more you know they will be the right part, or sell the piano to someone who can repair it. You can be 99% sure that installing a pair of working DACs will get you up and running. I think it's extremely likely that you got burned with counterfeit parts.