I just build the K 8021, everything works fine except the standbye LED doesn’t work… 
Any suggestions?
Did you check the led, does it work?
Is the polarity OK?
Yes the LED is fine. I checked it with a 1K resistor and a 9volt battery.
I also swapped LD-6 (the standbye led) and the LD-5 (+6dB led). In this position (LD-5) the former LD-6 is working well but now the former LD-5 is not working in the LD-6 position :-/
When installed like the assembly manual says and I disconnect the cathode of the LD-6 from the PCB and connect this to the - side of a 9volt battery and connect the + side of the battery to the (transformer side) of R42 (1K) the LD-6 is working. When I reconnect the cathode to the PCB again, LD-6 is not working.
I hope this give you more information to solve my LD-6 problem.