I haven't seen any evidence that he has a 5V supply. He could still run the 555 off +12V and use a voltage divider to get 0-5V. Looking at the mute control equivalent circuit, I suspect that Vcc would work just fine for muting.Hello,
I have looked at the datasheet.
The transistor can be ommitted.
The NE555 when powerd at + 5 Volts will drive the mute directly.
I notice that no one (including me) has corrected the STB input on the schematic. As I explained in post #10, it needs to be connected to Vcc to turn the device ON.