Try this: Hold Alt+Ctrl, click on the PC-76 meter, then drag up/down. The little meter screw turns. Anyone know what this does? I can't hear a difference, but I might not be listening for the right thing.

Oh really, what does it do?  Not in from of Sonar at the Moment...
 

It tightens or loosens the screw.  You don't want the face plate falling off.
 
On a real VU meter it calibrates the meter. A certain input voltage should give a certain deflection. 

Not sure it does anything in the PC-76. In the PC4K bus compressor, turn the screw, click in the meter and the meter color changes.

Yeah, it's supposed to cause a "backlight" glow on one of the modules (as scook noted) so maybe someone left that code in intending to implement that or just didn't strip it out.
 
Does nothing to the sound... and the backlight thing is a little silly IMO but I guess some people like that type of thing. I guess maybe the original hardware models have that or something. I guess it could possible create a color contrast more appealing to some users with visual issues but it does seem to be just for show.
 
The PC2A/CA2A screw is MUCH more interesting.
 
;-)

OK, I am back in the Lab and I have Held Alt+Ctrl and then clicked on the PC-76 meter and I don't hear or see a change in anything.   I do however, see the screw moving, but that's about it.
 
What am I really missing here?

Jesse G
OK, I am back in the Lab and I have Held Alt+Ctrl and then clicked on the PC-76 meter and I don't hear or see a change in anything.   I do however, see the screw moving, but that's about it.
 
What am I really missing here?

Absolutely nothing. It's just a graphical thing that is likely just leftover code for the module scook noted where it merely turns on the pale blue "backlight" on the meter area.

I thought I recalled that it did actually do something, HF bias or some such. But I may be recalling wrong.
 

...wicked
I thought I recalled that it did actually do something, HF bias or some such. But I may be recalling wrong.
 

Are you thinking of the CA2A? That screw alters how the compressor affects frequencies or some such. I fiddle with it all the time because it makes a subtle difference on really frequency rich signals like distorted guitar (to my ears anyway). Not so much on less chaotic sounds.

It's an Easter egg, it turns the backlight on the PC4K buss compressor as Scook already pointed out, that's it.. To the best of my knowledge, it does nothing on the PC76.