Disconnect your Panasonic video mixer's power cable from the wall or surge protector supplying power to it.
Turn off all connected devices. Remove all of the cabling connecting the video mixer to peripheral components.
Touch the ends of the multimeters testing prongs to the metal contacts on the end of the mixers power cable. Select the "Continuity" function on the front of the multimeter. If your multimeter operates differently, you will need to check your specific multimeter's users manual regarding testing of a power cable.
Plug the audio and video cables into the proper inputs on a multipurpose cable tester, and select the "Test" function. Check your owner's manual for instructions if your cable tester works differently.
Replace any cabling shown to be faulty with new, working cables. Test your video mixer by plugging it back into your audio-visual set up, and try to use the unit as you normally do.