Troubleshooting:

The led is on, I have waited more than 1 minute and the unit does not turn on (nor the led turns off).

Possible reasons:
There is not enough voltage on R1
possible causes:
-If you remove the output tubes, the HV-delay won't start-up

-Voltage on R1 is not enough, check that you have at least 35 Volts across R1 if the amplifier have a HV voltage of less than 350 Volts, try bybassing Z2 or Z3 (sometimes you have to bypass both).

- If you bypass R6 and the unit switches on, the capacitor is not doing its job. Unless it is defective, I have found that new electrolytic caps sometimes need "reforming".
remove the capacitor and apply its rated voltage for 1 minute (observing polarity!) then solder the cap back.

Test:
With an insulated nose plier short circuit R6, the circuit should start inmediately, if it doesn't, check voltage at D1, should read 12 VDC, if it doesn't check voltage across each Zener diode.

For Revision B Boards