The typical OLED display uses commands to change contrast.  My last few posts have been focused on the secondary screen.   The secondary screen is a Yamaha part that doesn't have a public datasheet.   

Yes - but the displays are DC driven and contrast change is achieved by varying the DC voltage to the display. A specialized chip like the one 'missing' acts as a DC-DC converter to vary the DC voltage efficiently. 

You have an electronic background. Take a look at the specs and circuit diagram for that chip and see what you think.

OLEDs typically have integrated brightness/contrast in the module itself.  Each pixel emits the light you see unlike LCD that requires a backlight.

Again, I don't have the schematics.   The OLED part is going to be the same or similar to the Genos secondary display.  Either way neither has a public datasheet.

Someone tagged on a request for OLED brightness and I would contend that in all likelihood that this can be done.  Final determination would need the datasheet but it would be unusual not to have this feature.

From what I can see from Genos the LCD has a BL-PWM signal that can be used to dim the backlight and this is driven by a CPU GPIO (general purpose I/O - an output in this case).

That doesn't mean MODX/Montage M use the same scheme but Yamaha tends to reuse design ideas across products and generations.   You can check the schematics for a connection to the backlight pwm LCD signal and see if there's anything that can be programmed to modulate it (duty cycle) as seen on Genos with the CPU GPIO output.

You don't look at what's not there.  It really doesn't tell you anything.  As I said, the no installed components could be redundant and "just in case".   Or not.  

Not sure why you keep referring to an OLED screen - where did you get the idea the M models are using OLED?

Secondary (sub) screen part has similar specs as Genos's secondary screen.   Although Montage M doesn't specify this in their public literature that I can find, Genos does show the secondary screen as OLED on the specifications chart on their website.

And I'm commenting on the secondary display because it was asked in this thread.

Yamaha Montage team, please include dimming on the secondary screen. I will really appreciate it.

the Genos 2 has an LED (notwithstanding the p.125 manual reference to Live View OLED)

Secondary (sub) screen part has similar specs as Genos's secondary screen.

Yes - but they are both LED. The Genos 2 has brightness functionality (p.23 owner doc) and the 'chip' but the Montage M does not have either.

Not sure why we are continuing on this. 

Guess we both think the other isn't listening to what we believe is sound information presented.

... and I don't have the Montage M schematics so I'm not really sure what's there.  Just guessing based off of information from various sources.

That said, I'm not sure how I missed the technical specs or got wrapped around the axle looking at something else - but Montage M's sub display is shown not as OLED - so you're right.  The Montage uses LCD with backlight.  Those sub displays may or may not have a pwm input like the touchscreen has.  And likely they decided to just fix the brightness (backlight).

Still, take a look if the main screen has the backlight PWM signal tied to a CPU which would indicate it could be adjusted.