1979 Hitachi (NP9X-L chassis)

[zenith2134]

I have a very similar TV in my basement storage area. I see yours, too, has the ST button (signal tracker). They are good TVs with great CRTs in my experience. On some of my tube-fired sets, a thorough line-up of the IF section can and did totally remove the audio noise when lettering appears in the picture. On later sets, it has been less of an issue for me, but perhaps the same procedure would work?