[sdiy] ADSR circuit trouble

[Tom Wiltshire]

Dan,

The fact that the LED is lit suggests to me that the switch that  
controls it (U403A) is permanently set to +15V (pin 13).
You could check that the voltage at pin 11 is switching. It doesn't  
look like it is, but if it is, then the 4053 is at fault.
If not, then the problem is further back, perhaps the LM358 U402A.

Let us know what you find.

Regards,
Tom