DENON AVR-3801 won't power-on.

[spytek]

Have Service Manual and Schematics but don’t know how to find the circuit that turns on the receiver and allows the AC power to flow into the power supply. By-passed (jumped) the relay that opens the “hot” AC line and made direct connection to the power supply. Some circuits went on and there was heat, but the unit was not fully powered on, the controls did not work, and the display was dead blank. These are the two problems: Transformer functions when jumped. But the “standby” switch is dead and won’t power-up the unit. No display when system is jumped. I hope someone who solved these problems might share their solution.

[Guest]

If this unit uses a switch-mode power supply, many power-on failures are caused by defective electrolytic capacitors. In order to test them you will need an ESR meter. EVB makes a good one and you can find them via their website. I usually wind up testing every capacitor to find ones which are dried up and open circuit. There's usually a small switch-mode power supply which runs a bunch of standby circuits and when you push the power-on button, those standby circuits trigger the relay. Because the standby power supply runs all the time, the capacitors in it tend to dry up with age.

Your problem may be unrelated, it's hard to diagnose these things over the web!