1950 Zenith Porthole Tuner Mistake

[VA561]

My Zenith porthole set was playing great every time I turned it on. The other day I turned it on and there was nothing but raster, no picture from my dvd player. I checked all of the connections and everything seemed fine. I took the cover off of the tuner and very gently rubbed the tabs on the channel 3 and 4 strips with a very fine emory cloth to remove any light corrosion. The picture returned but now I’m getting interference on both channels. Is there anything that can be done to bring back a clear picture again? Any help is greatly appreciated.