I was repairing a NAD C390DD for my friend and tough I'll post the solution here too as this type of problem is likely to happen on other units and I did not find it documented in web prior to this.
Symptoms before fix
A) When powering on from back panel power button the orange 'sleep LED' comes on
B) After push of the on/standby button on front panel 1 click of a relay can be heard and the orange led turns blue ... display will so no sign of life. Not other relay clicks follow. The unit does not switch on.
Problem appeared to be in secondary PSU which supplies the +5V and after switch on the +12.5V.
The +12.5V power line showed only +4.5V after the step B. So clearly something wrong. Anyhow, longish troubleshooting later it turned out to be a fault in following capacitors.
Hope this helps someone in future.
Symptoms before fix
A) When powering on from back panel power button the orange 'sleep LED' comes on
B) After push of the on/standby button on front panel 1 click of a relay can be heard and the orange led turns blue ... display will so no sign of life. Not other relay clicks follow. The unit does not switch on.
Problem appeared to be in secondary PSU which supplies the +5V and after switch on the +12.5V.
The +12.5V power line showed only +4.5V after the step B. So clearly something wrong. Anyhow, longish troubleshooting later it turned out to be a fault in following capacitors.
Hope this helps someone in future.