If you do not need to run the S90 remote tools or editor, then you can use the S90 in class-compliant mode. Driverless, the S90 should communicate via MIDI to Windows.

I'm not sure what made the USB driver stop working. I'd probably first check the mode:

• Press [UTILITY]
• Select "MIDI"
• Press [ENTER]
• Cursor down to MIDI IN/OUT
• Set MIDI IN/OUT = USB
• Press [STORE] to write this to your Flash ROM

Beyond that, the MIDI-USB driver guide/troubleshooting shows that Windows may run out of MIDI devices (10 max) and cause driver install issues. The fix is to uninstall not only the Yamaha MIDI drivers - but MIDI drivers for all other devices as well. You mentioned a different MIDI interface. Not sure how many other MIDI devices you may have. So uninstalling all of those drivers as a debug step may help.

The other thing that could be happening are Windows updating and breaking things. I haven't done any research in this department - but I do see Windows updates (even fairly major ones) happening fairly frequently. This should have a fairly low probability - but it does happen. It's not easy to disable windows updates. But, if it were easy (and, btw, it's not), I would turn automatic updates off and only hand-do any OS updates. Creating a restore point before each update. And rolling back if anything broke. That would also mean having to test "everything" after each update. In which case - it would be easier just not to update. Or do so very infrequently.

Sounds like a problem with the USB port... make sure there is no physical obstruction by visually looking at the connection point. Is the connection firm or loose (inspect it for physical damage as best you can... any connection point is vulnerable to physical damage).

If all appears normal, save your data and factory reset the instrument.

If that yields no change in your situation... I have not heard of anything specific but although you may not have changed anything directly, your computer operating system is changing things on a regular basis (some time security changes require attention). From time to time both MicroSoft and Apple are guilty of making security changes that force you to re-establish drivers or you may have give permission to make restore what ‘used to work’... and since no one reads the licensing agreements (who can blame someone) and before you know it, you’ve agreed to a change that corrupts your current configuration. Drivers that require you to give a special permission to run, suddenly no longer run because the update wants you to jump through a hoop or two (for whatever reason), if they say it’s a ‘security‘ thing, you’re going to agree — again, what else can you do?

I’ll try to look into this, too, but saying that you made no changes on the computer doesn’t mean that Windows hasn't snuck one in there — it does not always need you to make certain changes. But usually when something like this ‘breaks’ something else, there are a plethora of support calls... you may want to check in with Yamaha Customer Support to see if there are any known issues with Windows 10... and the S90... which dates back quite a few years. If there are issues with legacy gear, and changes in Windows 10, they would be the resource for that information. And worth checking in with them before seeking repair.

After contacting Yamaha Customer Support, they may make a recommendation... authorized service center.

Thank you Jason and Bad Mister for your quick responses. It looks like I have a list of things to try. I'll get back to you when I have done so.

I have tried the following:
- Uninstalled two MIDI drivers and restarted computer. Did not help.
- Tried with a different computer, running Windows 7. Same problem. I.e. I don't believe this has anything to do with Windows 10 updates.
- Visually inspected USB port on S90. Looks perfect.
- Did a factory reset on the S90. Did not help.

It's starting to sound like a hardware problem, isn't it?

Problem resolved. It did turn out to be the USB port. I pushed and pulled the plug in the port more forcefully than before. When I pulled out and up on the plug, it connected, and so far (fingers crossed) has stayed connected. Thanks for all your help and suggestions.

Excellent. Glad you got it working and thank you for letting us know!