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Yamaha electronic piano keying circuit broken

Can anyone explain how these (non-touch-sensitive) keying circuits work? Is it some sort of capacitance trigger, since there are no electrical moving parts (only the key and the collapsible rubber cone move)? I got a Yamaha PSR-170 that someone (somehow) broke off the lower corner of the top keying PCB, so one key (C) doesn't work. The diodes are all fine (and aren't even near the break), but the interlaced, non-conductive ink "fingers" on the damaged key are broken. And the copper trace only extends to the main "hand" portion, not to the "fingers". I epoxied the broken piece back on and soldered the traces together, but that key still doesn't work. Anyone have any ideas, short of replacing the entire PCB, which is something like $30+ ?
Thanks,

Dale

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The interdigitated fingers are circuit traces coated with a very hard, non wearing, carbonized type conductive surface. If a board crack runs through this carbonized area, that is FATAL. Replace the circuit board.
Realize that these contacts drive high impedance CMOS circuitry so the contact resistance is often in the 200 to 1000 ohm range.

The silicone rubber domes contain a conductive rubber pills, often two of them. One contacts the fingers before the second and the time difference between those is the measure of "velocity".The silicone dome acts as the restoring force for the key.

The keyboard is scanned as a matrix. Strobe lines intermittently select the first and then the second of the finger patterns, ONE octave at a time. The octave, 12 notes worth, are read in parallel one at a time.

The diodes are "disconnect diodes" which preven sneak paths when more than one note is held that are in different octaves.

Posted on Nov 17, 2009

Testimonial: "Thanks! But I didn't see any domes in the cones, & didn't measure any conductivity in them or the traces(?) + this unit isn't touch-sensitive."

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G# and A# Ghost Notes!


First try looking in your transpose settings. Refer to your manual to see if any arpeggiation/unnatural chord settings were inadvertently created by you or made by another user. If you believe it is a software problem you can not solve, back up your memory bank, remove your memory card, and hard reset your keyboard. Insert your memory card and check to see if your problem still exists.
If it is a technical problem, it sounds like you may need to get it checked out by an engineer/repairman. Sometimes when a digital keboard's keys collect too much dust/debris they can trigger multiple keys that aren't being pressed. Think about it like a key getting caught on an upright piano and pulling back the hammer next to the one that was played. A digital piano works off of one or several printed circuit boards or PCBs. The printed circuits usually can not short circuit because the wires and circuits sit in fixed positions. If an alien conductive fiber or series of conductive fibers connects a conducter to another, or if there is any humidity inside your piano it may cause circuits to misfire when a circuit is connected in the area. This could explain why notes you are not playing are being activated in the area in which you are playing.

If you are in a humid area and you suspect that this may be the cause you can attempt to draw out the humidity before getting a an expensive diagnostic done. Find a box large enough to house your keyboard. [If it is on a stand take it off and] place it inside the box. Cover the keyboard with plastic wrap (so as to prevent any foreign objects from getting into the instrument) and very carefully surround the piano with white rice. Remove the plastic wrap, close the box and leave it alone for a few days. The rice draws out any moisture from the electronic components. Very carefully (again so as to avoid getting any rice inside it) remove the keyboard from the box; remove any dust from the body, face, keys, and other components. Try your keyboard now. If humidity/moisture on the PCBs was the problem it should be solved. If not it is time to take your piano for a tune-up.
Hope this helps!

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The PF-85 action works by having the hammers strike the contact strip, which in turn connects the trace patterns on the circuit boards you're looking at together.

Any dirt between the contact strip and the circuit board will cause the keys to not function correctly. You can remove dirt with rubbing alcohol (iso-propanol) and a cotton swab. The only thing on these boards is traces, contacts, and diodes so they are safe to handle...just don't get finger prints on the contacts.

You should also make sure that the white wires are plugged in all the way on the back of these boards. A loose connection will cause the problem you've described. As would missing screws!

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Yep! Each key has two contacts, These are often conductive rubber pills that are pressed by the keys onto circuit traces completing the circuit. One of the contacts makes before the other so the procesor can measure the time between the closure of the two contacts. When one of the contacts doesn't make, the velocity is sensed as MAXIMUM so it HAMMERS !!!

Your problem is a contact isn't making... Your probllem to fix it is to ACCESS the contacts to clean them. Clean the contacts with ONLY 99% isoprophyl alcohol and Q tips.

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The keys are broken and some at no sound can I order the notes and sound kit. Yamaha PSR-295 . Regards Elias


Hi, i think you can. You can go to any of the Yamaha companies around you area and explain to them the problem of the keyboard. They will give you good and quality replacement part for your Keyboard.

Make sure you go to only Yamaha company to avoid getting a wrong part for your Keyboard.Avoid road siderepairsforissue like this,it's more complicated to handle

I guess that will do.

Thanks for using fixya...

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Note that the volume of piano keys depends on the "key velocity" which is the speed that the key is depressed. This velocity is MEASURED by the time between closures of the two contacts associated with each key in this unit.

If some contacts have become dirty, then the volume of those keys will vary.

Clean the circuit board traces AND the conductive rubber "pills" using Q tips and ONLY 99% isoprophyl alcohol.

This involves dis-assembly of the unit and you may want to seek professional help with this if you are not electronically adept.

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The key contacts have gotten dirty. They are often a conductive rubber pill that is pressed onto a circuit board. There are two pills per key and the difference in time of those contacting measures the velocity and the loudness for a piano voicing.

The contacts need to be cleaned with 99% isoprophyl alcohol and a Q-Tip. Use NO other solvent. Clean all contacts while the unit is open.

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You did not specify your brand or model, but unless you are electronically adept, you should take it to a shop for repair.

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This may be a cracked or shorted circuit board.

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First thing is to clean ALL the key contact areas and the conductive rubber pills with 99% isoprophyl alcohol.

This involves dis-assembly of the key area. If you are not competent in electronics, best left to a pro shop.

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