MacMacMac So why only $4000 for this piano? There must be something terribly wrong with it, beyond the obvious volume knob and headphone jack.
Maybe. Or maybe the dealer got it for free or close to nothing, and prefers to sell it quickly. Often time for dealers fast turnaround on inventory is preferable to maximum possible profits, because of other costs such as floor space, fixed salaries to employees, etc. It may also be that their technician has some other work which is worth more money than this one, so their choice is obvious. Speculations, obviously, just to say that it could be as Mac says, but it ain't necessary so.
Well, it can be a loss, but not a $4000 loss. Action and cabinet, and even basic electronics must be worth something.
MacMacMac Note: That's true for ANY used piano.
Pete14 Test all the keys with the piano off (no sound) and look for any odd sounds coming from the action/keys (knocking, clicking, etc); also check that the keys are proportionally even in terms of height, and check for any excess side-to-side wiggling, or uneven spacing between keys.
That's good advice, but given that the N1X uses a quite common action, anything there can be relatively easily fixed, for hundreds at most, not thousands (this is much more easy than on a "regular" digital). The hard part to repair is the electronics, so my advice is to try that part instead.
Pete14 the dealer can give you a ‘store-warranty’ and assume all repairs and parts within the stipulated timeline (preferably two years, but considering these things are built like tanks, one year could suffice).
I suspect they would balk at this, but it's good to ask. Depending of your propensity to risk, and monetary situation, you can shoot even lower in price if they don't offer the repair and the warranty. You may be able to do the repair yourself, I've done some repairs on instruments I bought (well, remember this is one who is building a full hybrid from scratch as a DIY...)
Consider this: the N1X is current Yamaha model. This particular one may be out of warranty, but Yamaha does offer warranty and repairs. How bad can a repair cost if anything is found broken down the road? My speculation is that, even if something horrible comes out, it'd cost much less to fix than what you are saving. And some things have workaround: assume volume knob completely breaks the whole power amplifier, now what? Well, you can buy and install external speakers and amp (there is room underneath), or maybe just amp and wire it to the internal speakers. You can do that for much less than you are saving, so I'd say the price is good even if the volume thing is unfixable.
If it were me, in addition to what has been suggested you to test, I'd bring a laptop (or at least a phone with FluidSynt MIDI) and test the workings of the USB MIDI in/out and of the USB Audio interface. Those are extremely important, IMHO, for such an instrument, especially if the sound eventually dies. Also, try the Yamaha app to control it, to verify that all other things work fine.
Best of luck!