Hey, all you engineers out there,
I just took apart an electric piano (Casio CTK-500) because one of the switches broke. I figured, if I can't fix it, I'll circuit bend it. I believe I will be able to fix it, so that's not really my question.
Here's how the switches work. There is a plastic block with metal contacts glued to it. The contacts ride on the circuit board below, connecting the right "tracks" together for a given position, but there is a ball bearing on a spring lined up with grooves to provide an artificial "detent" when moving the switch. There is some kind of grease on the contacts and on the circuit board. But, so many sources I've read have warnings saying NOT to lubricate electrical contacts. When I think about it, that does make sense for a number of reasons:
If the lube doesn't conduct well, of course the switch won't work well (or at all)
If the lube is conductive, it might let current go through paths that it shouldn't (in a multi-position or multi-pole switch) causing erratic or unexpected operation, or worse, the lube could "run" or "creep" into areas where it shouldn't be and connect two things that shouldn't connect, ruining the device. Over-lubricating mechanical components can also have this effect if the lube "runs"
A lot of lubricants (oil in particular) are flammable. Flammable liquids probably aren't a good thing to have around a powered circuit.
Many lubricants attract dust and grime over time, and dirty contacts make for poor/intermittent connections.
With all that in mind, I was somewhat surprised to see the contacts greased like they are. At least there's not too much where "creepage" would be a problem, but how does it allow the contacts to work, without shorting the tracks at the same time? Having said that, I am somewhat surprised, based on the mechanism employed (metal contacts sliding on a circuit board) that the switches haven't had more problems, even with lubrication. The piano is around 16 years old.
The grease itself is (usually) nonconductive. It prevents arcing between contacts and without it the contacts are more likely to corrode.
Aluminum in particular should always have an antioxidant grease applied. When aluminum corrodes it forms aluminum oxide which is non-conductive. That corrosion in home wiring was a major cause of house fires back in the 1970s before aluminum wiring was banned per electrical building codes.
I think I'm understanding you. The contacts in question are "logic" switches and thus, do not carry a great deal of current. Thus, the "non-conductive-ness" of the grease probably wouldn't have much effect.
No, it isn't that the grease resistance doesn't matter to a low current switch. It is that it keeps it from corroding, and keeps dust and such out. Not just any grease will work. You must find grease specifically made for this. The wrong kind of grease will cause bad connections.
Hi, without a pic its hard to visualise, however, most switches that are design to switch logic at low current have contacts that wipe against each other as they come into contact.
This rubs through the grease to give metal to metal contact and hence very low resistance, the grease keeps corrosion down and to some degree surface wear.
Don't forget this is a Japanese piece of electronics, in built redundancy, live span, so the grease has probably out lasted the life of the piano, which was probably about 5years after manufacture.
Does the key switch just open or close a switch or is it two switches in one, one opens and another closes.
If it is two switches then its probably (I'm not sure what the piano officianardos call it) controls the relative intensity of each note when its key is pressed.
Tom......
ps It would probably make a neat arduino music box.
I suspect the grease you are talking about is ordinary petroleum jelly or vaseline. it is normally used in these situations since its properties are very similar to air. That is as long as it is not contaminated it will not hinder electrical contact. But it will prevent oxidation.
There is no such thing as an all-purpose grease or oil. Although sometimes companies repackage and give something a brand name to sell it for more. I worked on VCRs for years. You could by a tiny, tiny 1 ounce package of black molybdenum grease and an equally small tube of white grease for the various bits that need it, or go to an auto parts store and pay $2.50 for a pint of black molybdenum brake grease and about the same for a pint of white lithium grease.
Dielectric grease is readily available at your local auto supply house. It's used to keep tail light and other contacts from corroding from moisture.
TomJ
I bought a tube at my local Autoparts store after my weather station RJ11 connectors corroded up. I stuck a blob onto the connector, inserted it and it has been fine ever since. (years)
