Did you try to contact any other MOXF user and see what they say?
If this issue would have such an incidence rate (100% in your case), it certainly would be known.
A web search reveals nothing. Are you aware of any such occurrences being discussed on this or any other forum?
If this doesn't seem to be a known issue but it does happen only to you with each and every MOXF, then maybe there is something with your setup.

I'm curious to know what factors you're thinking about when you say "something with your setup". I run stereo feeds to my Yamaha mixer and it sends via XLR to my Yamaha Dbr12's. That's it. I don't use a computer or DAW so the parts/channels exist only within the MOXF.

These symptoms are intermittent. You have to spend some time working in Song mode if you're to have any chance of experiencing it.

It would probably not take but a few days to have both of the issues present themselves so I guess I will keep my phone handy and see if I can document it on video.

The sudden volume freakout (and I'm talking now about the NEW MOXF6) happens at least once per day/work session. I re-cue, hit play and suddenly ONE part is eardrum shattering loud. Not just a little loud -- it is at the absolute limit of volume. Of course I hit stop OR hit the Part button, curse, and continue working. If I were to try again, hit play with that Part armed again, it will be exactly as it was. The only thing I can do is to go to the channel strip, toggle the Voice in and out and this seems to reset it. This is not, as you can imagine, something that is of much condolence if I'm in the middle of a show.

The sluggish/frozen transport happens every other day or so. As I said above, when it starts dragging or not responding at all, I do a Song Store in case it's a matter of the processor being over-taxed. I can't honestly say that it has EVER made any difference. I can turn the synth OFF and reboot, but if it's "acting up" rebooting doesn't necessarily solve anything. When it is doing it again,

I've gone to extraordinary lengths getting the keyboards to an authorized Yamaha service department in Mexico and NOTHING is resolved. And when I sent my other brand new MOXF to an authorized Yamaha service technician in North Carolina he couldn't find anything either. The two newer keyboards will probably be out of warranty by the time I can get either of them to technician.

I'm curious to know what factors you're thinking about when you say "something with your setup". I run stereo feeds to my Yamaha mixer and it sends via XLR to my Yamaha Dbr12's. That's it. I don't use a computer or DAW so the parts/channels exist only within the MOXF.

It's already in my post: a web search and some searches on synth forums etc reveal nothing.
While in your case it's 100% percent incidence rate with that model.

This does suggest that the cause might be in your setup and your way of using those, since nobody else seems to have the issues.

Which is why I suggested it's worth discussing with other owners.

I've gone to extraordinary lengths getting the keyboards to an authorized Yamaha service department in Mexico and NOTHING is resolved. And when I sent my other brand new MOXF to an authorized Yamaha service technician in North Carolina he couldn't find anything either. The two newer keyboards will probably be out of warranty by the time I can get either of them to technician.

OK, so when the boards are put in a setup different to yours, nothing is found.

I'm reading through your description of the failure and do not see details on the setup. Maybe the setup is simple and does not need much to describe - but that would help to know.

This failure occurs with your MOXF plugged into only the MOXF's power supply and no other cable connections? No USB, no MIDI cables, no sustain pedal, etc? Other than the power supply if there are any cables or accessories connected - it would help to know what type of cable/accessory is connected, what port it is plugged into, and what's on the other side of this connection (if applicable).

Briefly, since I appreciate the feedback and want to be very clear about my set-up.

All of my equipment, synth, mixer, speakers draw power from an APC backup battery.

I do not use a DAW or a computer. Not in the studio and not on stage. Everything is programmed, recorded and edited directly within the MOXF and I use those Song sequences as backing tracks in my live performance. There are no other MIDI or audio devices going into or out of the MOXF EXCEPT, of course, the Samsung thumb-drive I use for storing and backing up sequences.

My sustain pedals are Yamaha F3, F4a. My expression controller is the Yamaha F7.

There is a Flash memory in the new MOXF6 I'm using currently. But the freakouts were happening before I ever mounted a Flash memory.

I use high quality 1/4 cables, 6 to 8 feet maximum length, to connect RT and LFT outs from the MOXF to a Yamaha MG10X U. I don't use the stereo channel any more, instead the LFT and RT feeds go to individual channels which gives me more EQ capability, compression, low-pass filter. Any effects and EQ is done WITHIN the MOXF so the mixer EQ knobs are only for tweaking things at the gig.

I have a Shure Beta58 mic in one other channel and that's it. The XLR outs from the MGX10XU go into a set of Yamaha DBR12 speakers.

This set-up is what I use at home or on a gig. Everything, down to the APC, is the same.

The volume problem occurs without the FC7 pedal plugged in?

The sluggish issue happens without a sequence playing?

I will spend the next week working without the FC7 and see if the freakouts lessen or are eliminated.

I can't say or not if the sluggish behavior occurs when I'm NOT in Song sequencing mode. When it starts acting up I will jump over to Performance and try some commands and buttons. The Play, FF, and such don't have any function in Performance mode, but the data wheel functions in Performance mode for scrolling through Arps and maybe a few other buttons.

I will report back in a week or so.

I have been working for several days now with both pedals, Sustain and Expression NOT plugged in. The volume issues continue. In case it is pertinent, the volume change is not always an eardrum shattering event, but a very obvious "raise" in the volume of that Part. For context, I almost always insert a 007 Command at the top of every Part because I have come to rely on using EXPRESSION 011 commands for the moment to moment volume changes throughout a Song. This allows me to lower or raise the 007 Volume to make subtle changes without having to edit the data in every 011 event.

And, again, the solution is to resetting things is to race past the end of the sequence, then leap back to measure one and 98% of the time that fixes things. That is, it goes back to exactly the volume level it was previously. (If the first method doesn't work, then I go to the Mixer screen and toggle the Voice back and forth once and that also works.)

Since it's quite noticeable I'm going to use my cell phone to record a video of the Song as I'm working on it, so there will be a reference point when, later, a Volume spike occurs and I do another video recording to offer a comparison you can HEAR for yourself.

OK. I've been making video recordings of the sluggish transport.

I've also recorded the spiking numerous times, but I wanted to make sure the pedals were not plugged in, or there was any other factor that might confuse things.

I finally got it and I'd like others to see this but I'm not sure how to make that happen. I can't attach a video on this forum and obviously a video with pic and audio is the only way to document this. I've reduced the video, btw, so it's ready to go out and I'm looking forward to getting some feedback, opinions and help!

I think it's vital that someone who represents Yamaha take a look at this. If there is some dumb explanation I would LOVE to know it, cause right now I've got 2 MOXFs that were supposed to be spares waiting for pickup from Yamaha Mexico City. The technicians there did NOT experience the symptoms (not sure how they even could unless they were to sit and do some editing). According to Yamaha, MX, diagnostics were run on the keyboards and they were pronounced to be in good working order. Which leaves me exactly nowhere in terms of how to proceed. I only know that my two "backup" units are NOT reliable for live performance.

The MOXF8 presently in Durham, North Carolina, was brought to a Yamaha authorized technician who also ran tests and found nothing, but believed me when I insisted it was really happening and, since the unit was still under warranty (purchased new-in-the-box from Guitar Center in March 2020) and there was no way I was going to own an 88 key MOXF and have it doing the EXACT malfunctions as my "spare" back in Belize. The technician contacted Yamaha in California and was told that the keyboard couldn't possibly be under warranty because it couldn't possibly be considered new merchandise! They also informed the technician that parts for the MOXF might not be available anyway! I don't know all the details since I had to leave the U.S. and couldn't take the keyboard with me. A friend collected the unit from the technician but I was never told whether anything was actually repaired or replaced or resolved.

Sorry you are having trouble. Reading through this (some of your trouble is user error - CC7/CC11 which may explain your volume spikes) but since it makes sense to start with the largest issues first…

Rather than shoot a video of your “sluggish transport”, please make the video outlining your personal workflow.

I say this because, if multiple authorized service technicians have tested your instrument and found nothing, there is nothing more we can tell you about the health of your instruments. There is likely nothing wrong with the instruments, technically speaking. The tests are very thorough. Besides we already know how the MOXF should behave, what we don’t know is your personal workflow.

Unless you feel that you are imagining the sluggish behavior, then by all means make that the subject of the video.
But that would be non-helpful; let’s assume the fact that you are getting sluggish behavior, and concentrate on detailing your personal workflow.

Starting by eliminating your backup battery.
Did you bring that along when you visited the authorized service centers? If not, why not?
What were their test results running your gear with that device?
Do they get a different result than you do?
Or did they not get to test the APC battery, along with the load you are asking it to run. Did you provide the technicians with the rated specifications of your battery, and the total load you are asking it to run? (that has a role in all of this as well). Particularly since you use the word “sluggish” - makes you wonder about things getting the right amount of current to run properly; and particularly because you mention loud spikes in volume - makes you wonder about getting the right amount of current consistently to run the synth, the powered speakers, etc., etc. (just saying).

We cannot help you as much as an authorized technician running the formal test routines on one of your actual instruments.
We can help you avoid workflow and setup errors that might be the cause of your issue… but, logically, you must start with eliminating your battery.
Can you work — for test purposes… with just the instrument, a pair of headphones and power coming direct from a non-battery source?
This way we can eliminate your battery power source as a possible source of sluggishness and volume spikes!

Let us know. Please talk to the parties involved yourself, if possible (relying on someone else leads to uncertainty on your part). This way you have the info first hand. An authorized service center, here in the USA, would test and inform you about any work they propose to do — and they get your approval before making any repairs; They can do no work without your personal approval; If/when they repair your instrument, if they need to replace parts, they will return (or offer to return) all broken and/or replaced parts… that’s how it works (USA). They do not fix your instrument and then ask you if you want it fixed. They identify the problem (Test routine) - and then report the findings to you.
Parts are, generally, available — the MOXF8 is still a current product! Yamaha stocks parts for seven years beyond the discontinue date (often far beyond that).

Thanks, BM, for taking the time to respond. Let me quickly address some things you mentioned.

1. I live in Belize (most of the year). It is a developing country and the power grid is extremely unreliable. Surges, brown-outs, fluctuations. TVs and fridges and other electronic devices get fried all the time and are nearly impossible to get repaired. There are literally NO musical instrument repair shops. Simply don't exist. I didn't feel comfortable entrusting my MOXF to a surge protector and assumed that an APC was safer and more reliable and worth the investment.

2. I went through a complicated process of private transport and border crossings (at the height of the pandemic) in order to get both MOXFs into Mexico and then Fed Ex'd to the Yamaha Mexico City service department. Sending along the APC was not really practical, nor would it have occurred to me.

3. The English/Spanish language barrier was formidable. I sent a looooong description of the problems I was experiencing, in both English and Spanish. I had no way to have a proper conversation with any of the technicians and all they had to tell me by email was that they'd run the diagnostics and there was nothing wrong with the keyboards.

4. The MOXF8 that I bought in Durham in March 2020 was NOT being run through an APC, because I was in the U.S. and didn't feel any more then a surge protector was needed. When THAT keyboard started doing the very same things -- volume spikes, sluggish/non-responsive transport -- that my keyboards in Belize were displaying I was shocked. So I left the keyboard in the U.S. with an authorized Yamaha technician who found nothing wrong. I have no idea what was going on between the technician in Durham and Yamaha in California. It certainly left me with a bad taste in my mouth.

5. My new MOXF6 here in Belize is running through the same APC as the two other 6's. In order to test whether the APC is the culprit means I have to go back to power straight out of the wall and/or with a surge protector. I don't know if all surge protectors are created equal, so it makes me a little nervous.

It sounds like my video of the volume spikes or transport sluggishness may be moot until some other factors, like the APC, can be resolved.

Tonight I played a gig and the volumes went crazy a couple times in the middle of my show! So, however, whatever, I'm desperate to find a solution for this.