Kenwood KDC-519 CD Player

are you sure you have power going to the red wire? the red wire needs to be connected to a switched (ignition) power source. the radio will not work unless both the red and yellow wires are getting power.

If its a flip down, or a detatchable face, you can always try cleaning the terminals on the back of the face. If these are dirty, they can causebad connections.

you need to purchase the correct bus cable

try the menu button , holding the fm/am button basically it is waiting for you to hit the security code correctly

there is a button under the back of the face in one corner, just press around the back of the face with the car on until you feel the button press in and it should open.

If not you may have a bad ribbon cable that is not too expensive to replace.

are you using any separate amp?- if you are the blue wire on the back of the radio is probably turning off when you use a cd(the blue wire is for a power antenna, the blue with a white stripe is for an amp)

Detach the faceplate and look at the electrical contacts on the back of it for damage/dirt - you can spray it with electrical contact cleaner. Do the same to the contacts on the head unit - it sounds to me like one or more of them are a bit loose or otherwise not working properly.

Check the ribbon cable the one connects the face to the main board,ussually that's where the problem is.
You can get it from pacparts.com parts number is J84-0121-12
You need to have some soldering skills to replace it.
Good luck

it needs a new ribbon cable. Some car audio repair shops stock these (mine does). Part is about $20-30. Labor will depend on the shop.

Check the wire braid going out to the faceplate. Although this is a fancy feature. it is very problematic. But usually it looks like a flat plastic strip with brown stipes on it. Sony calls it a flexible circuit board. after so many flips wires break the buttons stop working and when the face gets just is the right place it stops turning. but is repairable if you can order the braid from Kenwood about a skill level five to put in.