I have a single note that suddenly is not sounding on my MOX8. The C# two octaves and a semitone above middle C makes no sound no matter what voice or performance is selected. The keyboard has been sitting in an air conditioned studio, no accidents occurred.  Suggestions? Thanks.

It may help to use one of those cans of air, used for blowing dust out of computers, to blow under and around the bad key.

Unfortunately a single key doing that is usually one of the contact strips having a bad spot in it. Those strips are not expensive or hard to replace.

I tried the “canned air” around the key already. No luck :(

If it indeed a bad contact strip as you suggest, how do I proceed? I live on an island in Hawaii (Kauai) where there are no Yamaha repair people. Can I do this myself?

Any other possibilities for the malfunction?

Is anybody able to please advise me with my situation? I’d be truly grateful.

Here is a link to replacing the contact strip on a PSR-3000.
The MOX is easier to get apart and the contact strip is the same.

http://www.psrtutorial.com/music/projects/contacts.html

For partshelp Contact:
Steve Demming at Yamaha USA at (714) 522-9000.

Thanks so much for taking the time to help.

Replaced the contact strip successfully. Unfortunately that one note continues to not play. When I inspected inside the MOX8 the IC board looked nice and clean.

If I didn’t live on a small island in Hawaii I’d gladly take it to a Yamaha repair center but… shipping will easily be $200 back and forth.

Any other thoughts on what could possibly cause one note not to sound?  Much thanks.

There are two contacts per key on velocity-sensitive keyboards - key velocity is determined by the difference in time between closure of the first and second contact. For an 88-key board, that would require 176 connections if each contact was separately wired, but instead a circuit referred to as a “key matrix” is used, which greatly reduces the number of connections needed. Although not exactly like the MOX8, these should provide the general idea:
https://en.wikipedia.org/wiki/Keyboard_matrix_circuit
http://www.openmusiclabs.com/learning/digital/input-matrix-scanning/keyboard/

As an example of how a single key might not function…
If an initial key switch closure is detected (the contact and its diode are OK), but the second one isn’t detected (due to bad contact or diode), then this is seen as a zero-velocity event. That won’t trigger a sound, because it’s interpreted as Note-Off, rather than Note-On.

Presuming all keys other than the malfunctioning C# (C#5?) are working correctly, the matrix connections to the key scanning chip would have to be OK, since those connections are shared. That only leaves the contacts at the faulty key, the two diodes for those contacts, bad soldering, or damaged pc board foil at that key location as possible causes.

Although the pc board might look OK, did you actually clean the contact area? Gently rubbing with a cotton swab slightly moistened with isopropyl alcohol is usually sufficient. The area should be dried with an unmoistened swab. If that doesn’t help then inspect the diode connections, etc.

Do you own an ohmmeter, and are you able to do basic electronic troubleshooting?

Didn’t know you were in Hawaii - moister is a real concern for you there - be sure to keep the keyboard in a really dry place and small variations in temperature.

Thanks for the response. So appreciated.

Yes, I have an ohm meter. There were about 50 screws that needed to be removed, outside and inside, to access the contact strips, so I’d rather open and close one more time and check everything at once. So before doing so I have a few quick questions:

1. Are the diodes on the flip side of the IC board? What do they look like?
2. Are we just checking for continuity with the ohm meter? That I can do.
3 If it is the diode, would I be able to discover if that’s the case, and if so can I replace one myself?
4. Where do I look for “bad soldering”?
5. How do I find the “PC board foil”? I have no idea what that is.

Might as well do it all if I’m going to re-open.

Thanks so much for the help!

Jimmy

PS bgrosse, the humidity is fairly constant in Hawaii, and no different than Florida or Louisiana etc. Mostly the keys are in an AC studio, but thanks for the thought. Keyboard only 1.5 years old. Have 7 keyboards and have never had a key go out on any of them, ever. Best, J.

The diodes are small, 2-leaded, glass encapsulated components. They’re mounted in pairs, two per key (one for each of the two contacts). They’ll look something like the ones in Figure 4 of the second link I gave above.

Good diodes conduct current in one direction. If you measure the resistance across a diode, it should be low with the meter probes one way, and high with them reversed. Check a pair from a known-good key, and compare the readings to those for the nonfunctional key.

The soldering I was referring to was that for the diodes. A pc board is a printed circuit (the contact board in this case), and the foils are the printed “wires” on the board. Check using magnification for bad soldering of the diodes, corrosion, or crack(s) in the pc board/foils.

If you find a bad diode, it will have to be replaced by unsoldering it and soldering in a new one.

If none of the testing or inspection turns up an obvious problem, then the key contact areas on the board should be cleaned as I previously described.

I only went into the details because of the inability to get local servicing. If you feel uncomfortable with doing any of the above, I strongly suggest that you leave the work to a qualified technician. Better to pay for transportation and service than to possibly make the problem worse.

Thanks. Awesome help.

I reopened the keyboard, inspected the PC foils with magnification which looked fine, but cleaned them as you suggested anyway.

I checked the diodes with an ohm meter. Good ones acted as you said, resistance in one direction, not the other. The non-functioning C# also worked fine, so diodes ok.

The solder looked mostly ok, but there was definitely a different color to the solder on the non-functioning key, that is it was a dull grey where all the other diode solder joints were shiny (see photo attached). I checked with the ohm meter across the foil side on all three circuits. One was a little iffy--meter moved but less consistently. So I heated up the solder joint and put some new solder on that one circuit. The ohm meter worked perfectly after doing that.

Felt like I did everything you suggested at that point, so buttoned it up and… the key is still dead.  All other keys work.

Do you think putting in a new pc board for the top octaves would be the ticket now? Should a pc go bad after just 1.5 years?

I’m learning a lot for sure… and am truly grateful for your help.

Photo won’t attach. Only 1.6 MB JPG. Motifator issue?

No doubt about it - dull solder is a cold solder joint and needs to be re-soldered.

Dull solder can be due to corrosion. The pc board could certainly be replaced, but usually something like this can be fixed.

To attach the JPG, first zip it. I might have other suggestions once I see it.

Here is the photo before I re-soldered.

IMG_4667.JPG.zip  (File Size: 1558KB - Downloads: 452)