JVC RV-NB50 / RV-NB70 No Power Repair

First download the Service Manual from here elektrotanya.com. (extract the files with 7-zip)

If the device doesn't display anything and doesn't respond to any button, but the Standby LED is lit, dissasemble it and check if the Power Supply is delivering aprox. 14V to the Mainboard. IF that is the case take a close look at the 0.22F Supercap which is sitting right here: 

It is leaking electrolyte onto the board, which is quite corrosive. So, remove the capacitor and give the board a good clean. The capacitor is not really needed; it just serves as a backup power supply for the clock to keep time, if the unit is unplugged.

Now connect a multimeter between GND (Pin 1 of CN302, closest to the front of the unit) and VDD (Pin 5 of CN302, 5th pin counting from the front of the unit). You should read approximately 3.3V.

In my case, it was 3.7V, which is a little high but still okay. If you have no voltage there, check the 3.3V regulator.

If you have checked the 3.3Volt line, disconnect one probe from pin 5 of CN302 and connect it to the reset pin 4. You should read approximately 3.3V. If it is more than 0.5V below the VCC voltage or not stable, check the parts connected to the reset pin of the microcontroller.

The parts to check can be seen in the image on the left.

In my case, C307 was faulty and pulled the reset pin down to GND.

It didn't have a short, but when 3.3V were across it, it started to have some leakage current that was enough to pull the reset pin low.

Replacing it resolved the issue.