The auto power off feature physically moves the switch. I thought while I have auto power off turned on that my switch was sensitive and would easily be bumped to turn off. This wasn't the case - it was the auto power off feature.

I'm not quite sure what's going on with your Montage - why a feature meant to auto power-off the keyboard would seemingly be stuck activated all the time. There could be other conditions that also physically toggle the power switch in order to protect the keyboard from more catastrophic failure (similar to a fuse).

Just in case something has gone off the tracks - you can try turning off the feature by special key combination.

Source: https://usa.yamaha.com/files/download/other_assets/7/812097/montage_en_om_b0.pdf - page 15

Disabling Auto Power Off (simple method)
==========================
Turn the power on while holding down the lowest key on the
keyboard. An “Auto power off disabled” message appears
briefly and Auto Power Off is disabled. The setting is
retained even if the power is turned off.

It's possible that there's something else wrong here and the above will not help.

Take your instrument to an authorized service center.

Do not force it to stay On.
Do not force it to stay On.
Do not force it to stay On.

Take your instrument to an authorized service center.

I would really appreciate if I could get some technical assistance with troubleshooting my Montage 8. After only 3 months of use I started getting problem powering up the instrument; as I've already written, when switching the instrument 'on' the switch pops 'off'; after 4 months I can not power it up at all; The instrument was bought more than a year ago and it's out of warranty. I used to repair keyboard instruments professionally and hold degree in EE. I don't need, and don't want to send it to a service center for repairs. I have purchased the service manual, and determined that power supply is ok, I have +5V, +15V and -15V. There are no visible burned parts. At this point I need spare circuit boards to isolate the problem. Again, I would really appreciate if I could get some help from Yamaha; perhaps there is some typical, generic problem that Montage engineers or technicians know of. I've seen some similar post on this forum, and elsewhere.

Sorry you are still having issues... Not sure where in the world you are, but this is not a Service site. Warranty length, I imagine, can vary depending on where in the world you are... even if out of warranty that should not prevent you from reaching out to a MONTAGE qualified technician. Given that MONTAGE’s are sold around the world, the support for servicing them is regional, not centralized. This only makes sense given the fact that your unit was likely sold with the power cable and voltage for your region of the world.

You need to start by contacting, first the dealer (store) where you purchased the unit, and/or your regional Yamaha representative. They would be far more informed on how you can proceed, toward getting Parts or repair service.

If there is some known issue (there is none that I am aware of) your regional office would be aware of it and will be able to help you. The Yamaha offices are listed in the back of your Owner’s Manual.

Hope that helps. Let us know...

Thank you for your posts Jason and Bad Mister!

Here are links to two threads describing similar problem:
https://www.yamahasynth.com/ask-a-question/power-up-problem
https://www.yamahasynth.com/ask-a-question/montage-7-doesnt-start-help

According to one of the posts, Yamaha was aware of this problem and is looking into it.

I have purchased my Montage 8 from NYC Guitar Center on 14th St. and I reside in New York.

I have talked to Yamaha technical support - in Anaheim, I guess - about a month ago, but they told me that they can sell me parts and don't have anyone who could give me technical advice abut Montage?!?

Here’s a link to the search engine: Find Local Servicer

Select “Synthesizer & Music Production”
Enter your Zip Code
It should return several locations in the NYC area.

Call. I don’t know if they give advice over the phone... but no harm in asking. Triple S (across the river in Jersey have been fixing gear for pros for a very long time. It’s been more than 30 years since last I needed them. But they always came through for everyone I’ve ever referred there).

Thank you for your post Bad Mister!

I've done all that about a month ago. Triple S told me that the power switch features circuit breaker, a.k.a. automatic fuse and that there might be a problem elsewhere; i.e. there might be a short somewhere that brings down a power supply rail, which then triggers circuit breaker - which I all already knew. Also, Triple S said that they've already worked on Montage with this problem.

I've known of Triple S for about 30 years too. Are you local then, and do you know someone at Triple S personally? I can call them again, but I thought if someone from Yamaha ask them what was exactly the problem, they might be more willing to talk.

Sorry, no, I don’t know anyone personally. Why don’t you just have them fix it?

Same boot problem here, any solution?
https://www.youtube.com/watch?v=x-SMdWx04mo