Yamaha Electric Piano CLP550 no keyboard output

[dkneyle]

The audio power amps work fine, as proven by putting an audio signal into the AUX inputs. (It takes its power supply voltages from before the IC regulators used to power the mainboard.)
Sometimes the keys will respond with low level distorted sounds, but mostly do not respond.
No physical signs of damage.
The power supply buses to the mainboard are +12V, -12V and +5V. The -12V line uses a typical 79M12 regulator. That line is only -11.8; close, but from experience I thought these things were pretty much spot on. There is certainly a smell around the power supply area of overheating/burning but nothing obvious to be seen.
Any thoughts are appreciated.

Yamaha Clavinova Keyboard CLP-550 ROM Chip Failure

It has been discovered that the code inside the 3 main ROMs of the CLP-550 degenerates over time causing failure of the piano to operate. The technology of the time for those original ROM chips was at the very leading edge of density, hence the cause of the eventual failure.
Through the efforts of many enthusiasts we have recovered the code for these ROMs and make it available here. Use an EEPROM burner to burn the attached binary files. Current EEPROMs to use are type 27C040

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[redwire]

Re: Yamaha Electric Piano CLP550 no keyboard output

I found the service manual here: CLP-550 Service Manual

I would use a signal tracer and work backwards from the AUX/headphone output jacks. I'm assuming the Mute relay is working?
The Master Volume potentiometer is upstream, look for audio there, then you are into the VCA's and DAC and Left/Right mux's.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

Thanks Redwire. I had tracked down a service manual with the circuit diagram. What more can you tell me about the Mute Relay? I see there is one for the headphones to switch out the speakers. I do feel like there could be something simple I'm missing here. I ran the self-test, the appropriate LED flashes, and the manual says "CLP550 failure". Doh! I also noticed that the DAC is warm to the touch. Not red hot, but no other ICs get warm. I wondered whether that was normal or not.
I agree with your approach of working backwards, but I would tend to use a signal injector, knowing that the power amps work. However once we move backwards from the analog to the digital I'd need a different approach.
Any further thoughts you have are greatly appreciated.

[redwire]

Re: Yamaha Electric Piano CLP550 no keyboard output

The 79M12 output spec is -11.50 to -12.50V, so I would not worry about it unless it runs really hot. The DAC usually run quite warm but not hot, as in can't keep a finger there.
I have some ideas to track it down, but it seems the piano knows it has a fault yet I cannot see any signal from the entire analog section that goes back to the micro, which would allow it to see a fault. So I'm a bit suspicious of spending time in the analog section. Look at the voltages on the mux's, the +/-6.5V rails will tell a lot.
There appear to be three mute relays. One for the power amp, one for aux out, one for option out. They should click, unless they are staying off=muted.

I wonder if a key switch is stuck. Once I went on a goose chase only to find that.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

I've been tracing back the audio as far as the analogue output of the mainboard. I can inject a signal at that point and all seems quite OK with the audio amplifier section. I’m just about to try injecting a signal at the outputs of the DAC to confirm that the whole analog chain is OK.

If I disconnect the piano key cables into the mainboard will that cause the CPU to go into another fault condition?

I agree that the -12 volts is probably OK.

Tell me more about the MUXs and the +-6.5V rails. What will that be telling me?

You seem to know quite a bit about these? I've taken up fixing flat screen TVs as a hobby and this was thrown at me because "you seem to be able to fix anything electrical". What's the chances of getting a second-hand board for one of these? They are 25 years old; no chance I guess.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

I injected an audio signal at the outputs of MUX chips IC15 and IC16 (pin 5) and the signal travels through all OK. The 6.5 volt rails are within spec. Now I'm out of my depth. I need it explained as to what the MUX chips do in processing the output from the DAC. Not sure how to trace back further than this? I don't have a scope to look at digital signals.
If I leave it powered up for awhile I get the occasional screetching sound come out of the speakers at high volume. Not sure if this provides any sort of clue. If I disconnect the mainboard output from the audio amps it doesn't happen so I assume it's been generated somewhere on the mainboard.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

The Test Program in the Service Manual appears to have some typos (I believe). The 'Test Program Entry' is actually brought up by pressing A-0 and C-7 (not A-1).
I can't get any tone generator signal out of the test routine. However I can get it to run the LED test routine. This would perhaps suggest that the CPU chip is OK and running.
(The Test Program in the Service Manual also talks about an LED Display - but the CLP550 doesn't have one.)

[redwire]

Re: Yamaha Electric Piano CLP550 no keyboard output

I've repaired mostly Roland and Cordovox keyboards, but the approach is the same- an educated guess and trace along from there.

The screeching sounds like digital garbage (esp. if very loud) getting into the D/A.
Check for cold solder joints, by gently tapping a plastic pen on the PCB, or a visual inspection especially the jumper links, as they can have fractured solder joints. Keyboards get a lot of vibration.

This board uses a single channel D/A converter, then rapidly switches between left and right channels to create two channels (stereo). The 4053 muxes do this switching, and there is a 4051 mux for coarse volume control.
The mux's fail a lot, and then the 6.5V rail would then be wonky. Yours seem ok.

But if the keyboard has an error message after power up, then I check for stuck keys/buttons, then a fault in the digital section like a bad ROM or RAM chip. Is this keyboard still complaining about having a fault? The analog section cannot report this back to the MCU.

The test program 1 does check for stuck keys, but no mention of memory check.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

The Service Manual (p24) says to enter the Test Program and Test 1: Switch Check. (There is no instruction on how to initate this switch check so I'm assuming that it's done automatically as the test starts up). So I'm getting the CELESTA LED flashing after it runs the self test. To quote the service manual: "If the unit is CLP550, The CELESTA LED will light ON and OFF repeatedly". Now, I'm not sure what that's telling us, but my translation of Japanese English is that it's simply saying that a fault has been detected in the mainboard. Do you read this in anyway differently?
I have tapped the board hoping that might show up something, but to no avail. But I agree with you idea of cold/fractured joints. No harm to be done by running an iron over those joints.
You suggest that the fact that my 6 volt rails are pretty right suggests that the MUX chips are OK?
I also would suggest that I don't have a stuck key issue because the keyboard responds to the command to test the LEDs. I would have thought that if I had a stuck key then I'd not be able to make that command work.
One further trouble shooting option now that you have explained the job of the MUX chips. What if I was to inject an audio tone into the input of the MUXs, or the output of the DACs? Would that tell me if they were passing the signal?

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

I was just proding around on the board. The first MUX chip (IC14) generates a 50Hz hum (mains frequency) when I place my finger on the plastic case. NOT on any of its leads. The other two MUX chips do not do this, nor does the DAC. That just seems a bit odd to me.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

Further update on tracking backwards. I can inject an audio signal at the output of the DAC and it travels through the three MUX chips all OK. Comes out of both speakers as I suppose we'd expect. Now I guess we are into the realm of a digital fault?

[redwire]

Re: Yamaha Electric Piano CLP550 no keyboard output

If there is an audio signal path from the DAC to the outputs, then the problem is the DAC or upstream of that, in the digital chips, or a just a bad connection.

It can help to take voltage readings on all the DAC pins. I wonder about when it screeches, what makes it do that.

I'm asking a Japanese friend what the self-test Celesta LED blink is about...

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

I'm going to make a prediction that it's a bad joint, even though I can't force the issue by prodding around. My experience with fault finding is that it will be simple rather than complex.

The screetching sound often comes soon after power on. I can't recreate it by pushing or proding anywhere. Sometimes, just after power on, I''ll get just the sense of a distorted tone (very low volume) being output when I push a key. Again, try as I might, I can't recreate it. Usually happens about the same time as the loud screetch, but just because I get the screetch doesn't mean I'll be able to get the output from the key. I'll pull the board and get the soldering iron going tomorrow. I've run out of time today due to other commitments.
I'll also take those DAC voltage measurements and feed them back to you.
Thanks for taking the time to help me get this old gal going again.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

Feel like I might be getting close now. I was probing around the DAC taking DC and AC voltage measurements and sounds started coming through. I could hit a key and very distorted sounds would come out, often with incredibly long sustain periods. All sorts of cosmic synth sounds were emerging. I could not do anything to obtain a consistent result. It was especially happening when I probed around pin 4 of the DAC IC. Tomorrow I will remove the boards, touch up the solder joints and see what results.
What's the chances of a defective DAC? I was interested in an earlier post where you said your DAC gets almost too hot to touch. This DAC is only slightly warm; should I expect an operational DAC to be warmer?
If the soldering does nothing then I think we might run the experiment of changing out the DAC. That appears to be ~$25. Not too much for experimental purposes.
DC voltages for interest are:
Pin1 -11.8V
Pin2 0V
Pin3 +12V
Pin4 0
Pin5 2.4V
Pin6 0.3V
Pin7 2.2V
Pin8 -11.8V
Pin9 0V
Pin10 0V
Pin11 0V
Pin12 0V
Pin13 0V
Pin14 -10.5V
Pin15 -7.5V
Pin16 12V

[redwire]

Re: Yamaha Electric Piano CLP550 no keyboard output

Your DAC voltage measurements look fine. The PCM56 audio DAC dissipates about 0.5watt, so it will run about 50º-60ºC and have a bit of a shorter life.
Beyond this, you would use a 'scope and look at the bitstream into the DAC, it is 4 signals.

You can try freeze spray on the digital IC's, or listen to the raw DAC output with a signal tracer. The 4053 is some kind of envelope (volume) switch,
You have to know if it is just a volume problem or if the tones are way wrong. This tells you if the tone generator is sending something silly or if the DAC/analog section is quiet.

The screeching might be when you power up, if the rails come up funny (i.e. +12V up before +5V) or a bad reset signal.

The self-test Celesta LED blinking just confirms the unit is the 550, not the 350.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

I have resoldered all around the MUX chips, the various wire links, passive components, the legs of the DAC chip, etc. I think I can now confirm that it IS NOT something as obvious as a dry or broken solder joint.
I also changed out the -12 volt regulator while I was at it (just in case). That has brought the rail voltage back to -12.1 volts, but no difference.
Just to reiterate, I'm fairly certain that there is nothing wrong with the analogue stages. Injection of audio into the MUX chips and at the output of the DAC produces audio output with no problems.
Mostly now (and I don't know what I might have done to cause this to now be consistent), when a key is pressed there is some sort of distorted electronic sound emerging from the speakers. It is nothing like what would be expected, is of fairly low level, but it's something.
I'm now going to order a replacement DAC IC. There's no way that the DAC is getting anywhere near to 50 or 60 degrees C. It remains my prime suspicion and is easy and cheap to changeover. Unfortunately if it is anything else in the digital chain I suspect we are moving into the realm of uneconomical to repair, parts unable to obtain, or high quality desoldering/soldering techniques required.
I have packed the piano away for a few weeks until the chip arrives in a few weeks. After I changeover the DAC I'll post the outcome.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

I'm still waiting on the DAC to arrive. However reading some posts for other models of Clavinovas there's a preceeding chip that appears to fail. That is IC12, type LC9116A-105 (part number XC711A00). It's an ASIC (proprietry chip) and appears to be almost unobtainable. Any idea of just what it does? It's described as an 'SFD-2' but I can't interpret what that means for the life of me.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

Well, I've changed over the DAC chip; no change to the problem. I even ran a hot iron over EVERY solder joint just to be sure. Same strange sounds emanating from the speakers. Very loud screetching very soon after power on that settles down after a couple of minutes.

It was recommended to me by an E-bay seller that I do some testing with the MIDI ports. I'm going to buy a USB-MIDI adaptor and use my laptop to check the output of the CPU/Keyer and inject digital signals and see if anything comes out at the analogue level.

My suspect is now this XC711AO / LC9116A-105 chip. It preceds the DAC and seeing that other Clavinova users are reporting failures of this chip it does seem like the next likely suspect. However a search of the internet suggests that it might be unobtainable unfortunately.

[dkneyle]

Re: Yamaha Electric Piano CLP550 no keyboard output

(For people who might end up on this thread via a search engine I thought I'd give you the end of the story as it might help your hunt as well.)
I purchased a USB-MIDI adaaptor so I could see if the keyboard of the piano was working and inject a MIDI sequence and see if it progressed through the digital section of the electronics.
The MIDI-out worked 100%. I was able to use emulation software on the laptop and play music from the keyboard. When I injected a MIDI-sequence I got VERY distorted garbage (actually very little came out, but enough to know that it was trying to get through). So I had narrowed it down to a working CPU but something wrong between there and the DAC chip.
As a last resort I rang Yamaha and ended up speaking to a technician who had serviced these Clavinovas over the years and reckoned he knew off the bat what the problem was.
The mainboard (DM) was replaced by type VH727509 which comes from the CLP-570. Yamaha has no stocks left worldwide.
The common problem is that the waveform generator ROMs deteriorate over time (technology of the era). There are three in the case of this board. Yamaha's standard practise is to replace all three. Unfortunately their cost makes the repair boardline (~A$230); especially as the replacement of these chips can't guarantee a successful repair. Yamaha also warns that nearly all the other ICs are no longer available, making longevity of the piano a concern.
So this electric piano will now be scrapped. A sad outcome. I've invested quite a bit of personal time because I don't like to see beautiful machines like this die, but I think it's a victim of technology that was leading edge in its day. I wonder how many of today's TVs would still be performing after 30 years?

[stj]

Re: Yamaha Electric Piano CLP550 no keyboard output

me thinks yamaha is full of shit.
post foto's of the rom chips.

romes can be dumped - blanks can be programmed.
and rom can be replaced by flash.