Audio hum - Videokarma.org TV - Video

N8NM · #1 02-12-2014, 07:53 PM

Hi gang!

I'm finising up an overhaul of an RCA 14S7072. It's been recapped (paper and electrolytic), aligned, and overall is working great, but there's one thing nagging at me: When watching scenes with a lot of "contrast", I'll get a faint buzz in the audio. I'm reasonably certain that it's a stray signal being picked up early in the AF, before the volume control.

I can remember having other TVs that did the same thing back when I was younger beat-up old late 50's TVs were all I could afford, so, before I go digging into this, I wonder if it's normal (lack of shielding) or symptomatic of something going bad?

It's hardly noticable except when I use the DTV converter box to control the audio gain; you really have to pay attention to hear it when using the volume control on the set.

As you can probably tell, this is the first vintage TV I've restored. It's been a fun project!

If the consensus is that it's normal, I'm going to button this puppy up and enjoy it until it warms up enough to strip and respray the cabinet.

Thanks!

Steve

N8NM · #2 02-13-2014, 09:25 PM

I spent a little time on it tonight and basically came to the conclusion that it isn't worth worrying about and probably normal, so I put it back in it's cabinet and enjoyed a couple of hours of glorious black and white!

***Eric H*** · #3 02-14-2014, 04:52 PM

It's fairly common to have audio issues on old sets, sometimes turning the contrast down can help. I think the strong signal from sources like a Box or DVD player can overload them too, I have one DVD that causes the sets to momentarily lose vertical sync on a particular scene change, it does it on more than one set so I can be pretty sure it's the signal.

Some sets (Predictas for example) have a"Buzz" control on them somewhere but I don't think the 14S7072 does.

lnx64 · #4 02-14-2014, 05:10 PM

So basically the older sets need just a attenuation filter.

They sell those, cheap too..

N8NM · #5 02-14-2014, 06:56 PM

Hadn't thought of that. The output from my DTV converter is pretty hot, I'll try it with a pad in line and see what happens.

marty59 · #6 02-16-2014, 12:44 PM

Try backing off the AGC a bit as long as you don't lose much gain but I suspect the buzz will still be there. I've tried some various attenuation filters with the expense of losing some video clairity in the process.

Newer NTSC sets seem to do okay, but I would try to pad on both sides of your box if you are in a strong signal area.