I have a JVC R-X400 receiver and the display bulbs went out. I took the front panel off but can not see where these bulbs are located. Can anyone tell me where they are and how to get to them?

SOURCE: NO FRONT PANEL DISPLAY

If the display processor has failed, you are out of luck, but sometimes it is just the backlighting (bulb or LED) for the LCD display or if if nothing in that circuit has voltage, then you can usually track down the power regulator for it and fit that.
Hope Ya Fix It!

SOURCE: front display panel

Check for bad connections on the display pins themselves. Specifically, the ones on the ends are the power/ground pins.
Let us know if that resolves the problem. If not, we'll look further into the circuitry.
Dan

SOURCE: jvc receiver rx-555 display bulbs

Please refer to the locations in my comments for your service manual to change out your diodes. Your going to need soldering experience to do this and careful for the high electricity with the capacitors.

SOURCE: My C720BEE receiver is silent.

Please note if you are getting a clicking noise from the amp 4 seconds after switch on ( that is when the power light turns green from red ). If you are not-- it indicates an output short or failure and the protection circuit has not connected your speakers to prevent further damage.
You will have to get professional help to get it fixed.
One simple thing you can do is to disconnect all the speaker from the amp and turn it on and see if you hear the click- that would indicate that one of your speaker is damaged or shoerted, you can tryu it one by one.