Yes, questions about electronic music instruments are on topic.
Yes, questions about the use, care, and repair of instruments are on topic.
Yes, questions about specific instruments are on topic.
Explanation:
Yes, questions about electronic music instruments are on topic.
We don't discriminate against certain types of musical instruments here. If it is an instrument that can be used to make music, it is welcome here. We already have lots of questions tagged electronic-music, synthesizer, and midi.
Yes, questions about the use, care, and repair of instruments are on topic.
From our FAQ:
What topics can I ask about here?
Musical Practice and Performance Stack Exchange is for musicians,
students, and enthusiasts. If you have a question about...
practice & performance technique
music theory and notation, history, or composition
instrument maintenance
usage of specific music software
... then you're in the right place to ask your question!
Yes, questions about specific instruments are on topic.
By specific instruments, I'm referring to a particular make of instrument, rather than the type of instrument; for example, asking a question about my Flea ukulele rather than not telling people which ukulele I have and making the question as generic as possible.
This seems to be the controversial one, but I'm not sure why. Of course, we want the question to contain as many details as are needed to be able to provide a good answer. In my ukulele question, if I hadn't specified which ukulele I had, no one would have known that it has a plastic bridge, which is unusual for ukuleles, nor would anyone have known that the manufacturer of that particular ukulele has a very generous warranty on their instruments. In another answer on this question, Alexander Troup indicated that he would vote to close a question about modifying a guitar if it included a particular make of guitar. It seems unthinkable to me that we would close an otherwise good question because the asker gave too much detail about their particular situation. A good question has lots of detail; a bad question has little or no detail. I don't know much about the Ibanez Universe 777, but if there is something unique about that guitar that makes scalloping frets a different process than with other guitars, then it is an important detail, and should definitely be on topic. Often, the asker doesn't know which details are important (because they don't know the answer), so we want to encourage as much detail as possible.
With some instruments, make is less important. For example, most trumpets are similar to each other, no matter who makes them. (At least I think so, I actually don't know much about trumpets.) With other instruments, especially electronic instruments, every make is different. Sure, keyboard synthesizers all have keys laid out in a piano pattern, but all of the other buttons are different on every keyboard. When asking a question about keyboards, the specific keyboard being played is crucial information.
At one time on Stack Exchange, questions could be closed for being too localized. The idea was that we want questions and answers to be useful to more than just one person. However, this is hard to judge. How do you know that no one else will ever have the same question? Sure, you might never buy a PSR i455 keyboard, but that doesn't mean that there aren't other people that do have them. Stack Exchange has since gotten rid of "Too Localized" as a close reason network-wide. There are other reasons to close, but the question we are talking about doesn't meet any of them: the question is not a duplicate of another one, it is not off topic, it is not unclear, it is not too broad, and it is not primarily opinion-based. Therefore, it should remain open.