Oh Yeah ... I'm using an S90 and 3 Plug-in boards

Welcome to Yamaha Synth!

Sorry you are having difficulty with your S90. If you truly believe you know how it should work and have concluded that its behavior is inconsistent, then you should take it, immediately to an authorized repair center. But if are at all not sure about how to recall/setup a Performance with PLG150 Voices assigned to some of the PARTS, then we'd be happy to try to help you accomplish this goal.

But which is it?

In order for whatever we say here to help you, we will have to use the *correct terminology* - as used in the S90 Manual and on the S90 screens.

Here are terms you used that we don't understand right off the bat:

"...sporadic loading glitches" - what is the error message? Does it identify the SmartMedia card or other device you are using? Is there an error message in the screen. What do you define as a glitch? Is it a noise or interruption in the sound? Or are you using this word to mean something specific?
"...load a patch in Master Mode..." - there are no Patches, we are not sure exactly what you are doing and you don't really say. A MASTER Program addresses either a Voice, a Performance, or a Multi/Mix. You cannot load just Master programs alone, what type of file did you load... What is the exact File name and extension. (.w4e) or (.w4a) or (.w4v), etc.? Do you actually mean "load" as when loading from a file, or are you using load to mean, building a playable setup in Master mode?

What other PLG150 Boards do you own?
What slots are they in, 1, 2, and 3? It makes a difference!
For example, is the PLG150-AP in slot 1 (orange), slot 2 (yellow), or slot 3 (green)?
How is the PART identified P1, P2, etc.
What firmware is your S90 running?
the fact that your PLG150-AP works in Voice mode (you call it "single" mode) tells us the S90 and the PLG150-AP board are fine.
Sounds to us like you are unaware of how to assign a PLG PART to a play in combination with others (either in Performance or Multi/Mix modes). If this is true, let us know... we can start there

If, however, you are aware and have been playing/using your S90 normally since 2002, and what you are describing is something new that started happening suddenly out of the blue, then please tell us which Voices are assigned to Part 1, Part 2, Part 3 etc. And are they assigned to Parts of S90 Performance, or a Multi?
When the Master mode program is recalled, which other mode lights are lit?

Please let us know.

Thanks for the quick & thorough reply, Bad Mister! I'll try to explain my dilemma in correct terms. I was using the word "load" to mean "recall"
I'm having problems recalling PLG150 Voices assigned to some of the PARTS in a Performance. The PARTS with internal voices assigned always recall normally but the PARTS with
PLG150-AP voices will sometimes recall and sometimes not ... resulting with silence rather than my AP voice.The proper Plg Lights This problem only occurred occasionally for a couple of years.However,the last few months, it's happening A LOT. I been wondering, could it be a problem with my internal battery? It it needs to be replacing for sure.

Regarding my comprehension and skill in programming the S90, I've been experimenting in programming, editing & creating voices, performances for years and have studied & utilized the wonderful master mode for almost all my live playing... I love my S90 ... also a big thanks to Phil C's literature. I don't at all mean to sound arrogant just want to communicate my understanding. Still, this problem has me stumped!

My Hardware set-up: S90 with PLG150-PF in slot 1, PLG150-AN in slot 2 and PLG150-AP in slot 3
Firmware: unknown. pretty sure it's the original.

Note: I have two PLG150-APs and tried swapping them from my motif rack .... no change in the problem.
Note 2: When the Master mode program is recalled, the proper mode lights are lit.

Thanks again Bad Mister and anyone else who has an idea for me!

Forgive me for asking the qualifying questions about your skill level, I'll be honest, the S90 is at that edge of memory point for me. At one time I knew just about every thing there was to know about operating an S90 with the PLG150-series boards, but time passes. If you have been a user consistently since that time it is probably true, that you are more familiar with operating it than I am. Certainly I've not operated an S90 in almost ten years.

And I respect how difficult it could be to navigate the multIple technologies that the Yamaha synthesizers supported back then via the PLG150-series expansion boards. These add-on boards were a double edge sword. They gave a variety of sounds and technologies but with that came complexity. The slots, the addressing and assignment of Voices to Parts, etc., could be tricky.

The way we will tackle this is, between what you know about the S90 (I don't have one here to touch and look at) and my knowledge (fading as it is) and with the help of the Yanaha Customer Success team, we'll piece together the solution.

First thing - I recall that the S90 came out in 2002, the PLG150-AP didn't hit until around 2004, so you would have likely needed to update your S90's firmware to install the bank of Voices made for when this board was placed in a Modular Synthesis Plugin System compatible synthesizer.

So let's start there. Go to the following website:

http://download.yamaha.com

Select your country
Type in your MODEL NAME: S90
When the SEARCH RESULTS appear verify by clicking on S90
The screen will populate with items for the S90

Look for the FIRMWARE Updater.
This download will include detailed instructions which include how to verify your current version - please read these twice.
Read through them once completely so you'll know what you'll need and what to expect.
Read through them again as you proceed with the update.

If you are at all nervous or unsure please call your local Yamaha Customer Support folks or post back here.

It could be that once you update your firmware, the issue you are having with the 150-AP board may go away. Anyway, it is a good reason to update, because I kind of remember the AP board could be used in product preceding it (Motif, S90, Motif ES) but there was data that needed to be installed in ROM. Products that came after 2004 had the data already built-in.

Anyway let's start with updating the firmware.

U R BAD ... Bad Mister! ... I think you've solved the problem!!!

Got a gig tonight & I'll let u know.

many many many thanks!

After updating the firmware for my S90, I did some studio work and live performance this weekend and was able to recall Masters & Performances w/plug-in voices every time
with no problems! What a relief! .... feels like my S90 was "saved"!!! Thanks to Bad Mister who advised the update!