Trying to fix a Yamaha NP-30 (or similar)

[AnotherScott]

I'm using a Yamaha NP-30 which is mostly fine, but when I first turn it on, there is a a bank of 6 notes (from C# above middle C through the F# above that) that usually don't play, or if you hit them hard they may play very loudly with a constant repetition (like a mandolin) until release. (It's kind of odd how loud it is, in that it's far louder than anything the key could normally trigger.) After it's on for a while, it seems fine. (So maybe it's some kind of barely touching connection that solidifies when it expands with heat?)

 

Anyway, I was wondering if there might be a tech-type here on the board, someone who is somewhat familiar with the guts of these or similar Yamaha DPs, who can tell me whether this sounds like something that might be an easy fix, and guide me toward where to look and what I'd be looking for. I'm trying to avoid bringing it in for service, since (a) it works fine after it's on a few minutes anyway, and (b) the service place I know won't even look at a keyboard for less than $95, which seems high if it's really simple and especially in light of the fact that the keyboard is only worth 200 some-odd bucks to begin with.

[MoodyBluesKeys]

Never been into an NP-30, but I was auth. Yamaha service center for a number of years. One possibility would be either a circuit trace, poor solder connection, or intermittent diode in the switching mechanism that is used for key switches. Most keyboards use some form of matrix that will have between 6 and notes on each section of a parallel buss that then goes into the computer and is scanned to determine if a keyswitch has been pressed.

 

If it goes beyond that, most of the Yamaha stuff, especially on the low end is one big circuit board with all the computer stuff, a circuit board for keyswitching, sometimes a board for panel stuff (switches, pots, lights, displays), and a board for power/audio. Sometimes these are combined into a couple of boards. Ordering a service manual is probably not justified, since it costs more to find a problem than the unit costs. All their warranty service was done by ordering a replacement board, and returning the old one - they had a service center somewhere that triaged the old boards.