Had digitals since 1986 or so; never had a keyboard cover, or a lid. never had a problem either from contamination. I would suspect some other cause.
Wear can also be a cause for the kind of intermittent problems that arise with the contacts / sensors / suction cups / nipples that reside between the underside of piano keys and the electronics /sound board..... do we have enough descriptive names for these small albeit important components? Does anyone know what materials these are made from? Iâ€™ve seen some people mention rubber, which may be true, but are these not conductive contacts?
From frequenting this forum a few years now, it seems that this problem is somewhat common with various brands to include Kawai and Yamaha and when it occurs, does not always exhibit the same symptom IE. the familiar â€œa keypress resulted in no soundâ€. When it began to happen often with my ES7, often it was â€œkeypress that produced no soundâ€ but at times it was â€œkeypress that produced distorted soundâ€. Kawai put me in touch with a certified tech who, interestingly, was also a certified Casio tech whoâ€™d tired of dealing with Casio Corp. He kept the DP a couple weeks, during which opened up the DP, did not really see much in the way of debris but used compressed air nonetheless because â€œ it does not always take a lot to cause this problem .... perhaps a bit of misplaced hair or dander is all it takes sometimesâ€. He also removed the contact strips ( for the octaves wherein I had noticed the intermittent problem) so he could closely inspect visually and remarked that some of the contacts showed a telltale sign of wear - a visible sheen instead of uniform dull grey color. This occured during the second year (approximately 13 months from new) of regularly playing 2 or more hours a day. By comparison, Iâ€™ve not (yet) experienced same/similar problem with my Roland DP. I have not seen many Roland owners experiencing this phenom compared to, for instance, Kawai.