I just installed the C4S upgrade. The instructions that were included were for the 2.1 kit, but I was able to piece together what was needed, or so I thought.
I have the C4S installed along with the new power supply resistors. Voltage at input of the C4S is about 400v. There is almost no voltage on either OA or OB and LEDs aren't lit. Sound output is minimal.
POSSIBLE SOLUTION: I see the 2.1 instructions include a ground attachment. I don't have this implemented (no clear instructions). What's the next step?