Yamaha CLP-880 ghosting issues

[shivasage]

Hello everyone. In the past couple months my Yamaha Clavinova CLP-880 has become unusable due to unwanted notes sounding when I press certain simultaneous keys. For example, when I play a C and C#, I consistently hear the upper F#. This issue is identical in other octaves. I removed the key-bed from the action and the issue persisted, so therefore the action cannot be involved. On the key-bed itself, I have tested the capacitors and diodes and they're all working properly. I also added pencil lead on all of the carbon contacts.

The only remaining part on the key-bed is the IC, Yamaha YMZ702-D. I was able to find this for sale on eBay for about $15. As another alternative, I could replace the entire key-bed for $100. I am hoping the issue is in the key-bed, but these tests haven't precluded the possibility that the issue is in the motherboard, which I was unable to find for sale.

I understand broken traces could also be the culprit, but my instinct tells me that would result in notes not sounding, as opposed to unwanted notes. I also don't think I'd have any efficient way of looking for broken traces (I'm just a newb hobbyist in electronics DIY), but I suppose it could be possible.

Any thoughts would be greatly appreciated. Thanks!

 

[rock soderstrom]

Hi shivasage, welcome to the Group!
It could actually be the keybed scanner chip, I had a similar problem with an organ. I suspect the chip is not socketed, either you need a pro desoldering machine or you have to cut the chip out. Ideally you would need a replacement keybed for temporary testing, otherwise you will have to invest the 20 bugs on spec for the new chip.

Unfortunately, there is also the possibility that the problem is in another part of your Instrument.

A second keybed would be really great to encircle the problem area.

 

[shivasage]

Hi shivasage, welcome to the Group!
It could actually be the keybed scanner chip, I had a similar problem with an organ. I suspect the chip is not socketed, either you need a pro desoldering machine or you have to cut the chip out. Ideally you would need a replacement keybed for temporary testing, otherwise you will have to invest the 20 bugs on spec for the new chip.

Unfortunately, there is also the possibility that the problem is in another part of your Instrument.

A second keybed would be really great to encircle the problem area.

Thanks!

When you say 'scanner chip', are you referring to the IC I mentioned, e.g. the one you can see in this picture?

https://i.ibb.co/41sNRD2/PXL-20220806-004054616.jpg

Unfortunately I don't any other key-bed to test it with. I think I'd be able to manually desolder it, if perhaps there is some other way to check if it's working as intended.

 

[rock soderstrom]

Thanks!

When you say 'scanner chip', are you referring to the IC I mentioned, e.g. the one you can see in this picture?

https://i.ibb.co/41sNRD2/PXL-20220806-004054616.jpg

Yes, that's the one I'm talking about. It is a proprietary Yamaha chip that reads the key states - a keybed scanner.

Here you can find some (unofficial) info:

https://paulbanks.org/download/files/ymz702keyboard/YMZ702d.pdf
See also the service manual for the CLP 920 in the attachment (schematic at the end of the dokument). It might work similar to your CLP880.

Before you remove the chip I would try to find the error with the diagram in which you learn how the keymatrix works in your instrument.

If indeed the YMZ702-D is defective, then replace it. Heads up, the PCB is made of hard paper (Pertinax?), the tracks and soldering eyelets come off very easily when desoldering. It is best to cut out the chip with the side cutter and rather make sure that the PCB survives this.

Good luck!

 

[shivasage]

Yes, that's the one I'm talking about. It is a proprietary Yamaha chip that reads the key states - a keybed scanner.

Here you can find some (unofficial) info:

https://paulbanks.org/download/files/ymz702keyboard/YMZ702d.pdf
See also the service manual for the CLP 920 in the attachment (schematic at the end of the dokument). It might work similar to your CLP880.

Before you remove the chip I would try to find the error with the diagram in which you learn how the keymatrix works in your instrument.

If indeed the YMZ702-D is defective, then replace it. Heads up, the PCB is made of hard paper (Pertinax?), the tracks and soldering eyelets come off very easily when desoldering. It is best to cut out the chip with the side cutter and rather make sure that the PCB survives this.

Good luck!

Thanks for the resources.

I'm not sure how I'd be able to diagnose the error in the chip. I've read some things about key matrices so I have a basic understanding of they work. Given that the keys are grouped into groups of 6, and the ghost notes are pretty consistently 6 notes away, it seems the error must be in this part of the instrument. The only part I was unable to test is the 3-terminal ceramic resonator which is connected to the chip. Perhaps these can wear out? I don't believe I have the equipment to test this part. If I buy the chip and the problem is the resonator, that would be a waste.

I also realized that if I decide to replace the entire PCB, to save money I could potentially only buy the lower half, as it includes all of the electrical parts. But if the issue is caused by broken traces, then this wouldn't be a good idea.

 

[rock soderstrom]

I understand broken traces could also be the culprit, but my instinct tells me that would result in notes not sounding, as opposed to unwanted notes.

That only sounds plausible at first glance. AFAIK there are also key scanners that work with openers, i.e. the note-on signal is triggered by an open contact. I don't know if this is the case here, but you should definitely consider this before replacing expensive components. Cracked traces caused by key pressure are definitely a possibility.

 

[shivasage]

That only sounds plausible at first glance. AFAIK there are also key scanners that work with openers, i.e. the note-on signal is triggered by an open contact. I don't know if this is the case here, but you should definitely consider this before replacing expensive components. Cracked traces caused by key pressure are definitely a possibility.

Yeah, that makes sense. I think my best course of action is to replace the entire key-bed. I might replace it one half at a time, by starting with the half which contains all the electronic parts.