Cobra 25 nightwatch face plate

You have to have the whole thing replaced and it's almost as much for a new radio so I am told.

 

Mr. Turbo T, is correct. I can only guess the blown part of the faceplate is shorted and causing the hum. I have seen mods to disable the nightwatch feature, although I have not personally done one. Have always avoided the nightwatch and sound tracker models. You would have to buy the faceplate from Cobra or find a junker with a working faceplate. Be forewarned... The nighttracker feature is notoriously delicate and pone to failure.

 

I concur with my learned colleagues above. The faceplate is an electroluminescent panel, much like those bluish or greenish nightlights that run in your house for about two cents per year. It's constructed in sort of a mesh. It's powered by a teensy 140 volt *a.c.* power supply fastened to the side rail of the chassis. The voltage gets spun up that high in the same way that a photoflash or defibrillator do: a high frequency oscillator keeps pumping in pulses from the 12 volt DC line that runs the radio, but differs in that both the positive and negative pulses are added up to make a rough alternating current.

Older TVs that had an oscillator running at around 15 KHz and some folks who aren't of sufficiently advanced years can hear it, much like a mosquito's wing noise. It's supposed to be bypassed so it doesn't impress itself on the audio lines in your radio; if that doesn't work right, you can sometimes hear the whine through your speaker circuit. The shielding shell of the power supply also rattles like a resonator at that frequency, acoustically amplifying the sound, kinda like a tuning fork or a guitar's body.

I have a lovingly-restored Cobra 25 WXNWST whose NightWatch faceplate had mostly failed like yours due to a vehicle collision. At the time, Cobra wasn't accepting any new applications for servicing dealers, so I bought mine at retail -- about $33 plus shipping.

Sure, it's about half the price of a whole new radio, but I'd adopted the radio as a project, and it was just one more niggling annoyance in the project completion.

FWIW, the most frequent cause of a NW faceplate's failure is that little whiny power supply. To their credit, Cobra has standardized the power supply for all models with one replacement assembly. I don't know its cost, but IIRC it exceeded the cost of the faceplate.

Since part of your faceplate is working, though, the power supply is OK, and the fix is as described by others: replace the faceplate. Probably worth a little time at the grinder to thin down the walls of your sockets first, though.
HTH
73

 

Check inside the radio where the ribbon cable going to the face, and check and make sure the ribbon cable is plugged in good to the back of the faceplate and on the board...Also check and see if the ribbon cable runs next to the Mic jack...If the ribbon cable is right up next to wires running to the Mic jack, it can cause a hum...You may just need to cut the plastic tie straps holding all the wires in place, and separate the wires away from that ribbon cable...I had a Galaxy 939 that had the same problem, and that was the fix Galaxy Tech's told me how to fix it, and it worked.

Probably what happened is when you were jacking with the knob, you may have just pulled the wires loose a little that go's to the lights...

Couldn't hurt to check first before taking it to a shop.