Eml synthesizers

I have a question about the EML 100. In the output mixer section, 
there is a knob marked OSC3/EXT. When in the fully counterclockwise 
position there is nothing, but as you raise the knob OSC 3 drones. 
While it is droning, nothing has any effect on it. No ENV's or 
filter. It's as if OSC3 is patched straight to the output.

I would think that this would be incorrect. I would think if you 
turned the knob all the way to the right it would be all external 
sound? I believe on the 101 it is marked only as EXT. I don't 
understand why they would make a pot that would do essentially the 
same thing you could do just by patching a cord from OSC 3 output 
into the input in the output mixer section.

Any ideas?

Also on the 100 I have ENV 1 is non functional. It completely cuts 
the sound out all together if I selected ENV 1 in the amp section. 

Thanks,
Heath