View Full Version : non-grounded chassis question


frenchy
10-26-2010, 12:35 PM
This is regarding my really old tvs that have non-grounded chassis's, and the a/c plugs don't have ground pins. Many times when I'm hooking up antenna and/or coax wires and such to them for DirectTv and digital tuners, I notice that I'll get a good tingle from those wires when touching the other end (before I screw them into whatever tuner box I'm hooking them up to.) It's not like I'm getting B+ or line voltage on my fingers, but strong enough of a tingle where I think gee, is that supposed to happen?! I can get the same kind of tingle sometimes when touching some of my pinball machines, and I happen to be contacting the metal on an adjacent machine.

I'm guessing that this is just stray current that is due to these sets not being truly grounded, and that maybe I was touching something else that WAS grounded with my other hand or something. Is this a correct guess, or do I possibly have other problems? Sets include ones like a '50 Hoffman b/w and a '56 RCA color, both of which I totally recapped and which work great otherwise including all these hookups. I have these two stacked in my bedroom with hookups to my DirectTv etc. If this stray current is normal of sorts, is there anything additional I could or should do in terms of grounding or should I just forget about it? It's just the fact that I was only touching the antenna connections, not the chassis or something on it, seems like it should be safer than this.

Thanks!

Tom Albrecht
10-26-2010, 01:56 PM
These sets have a line bypass capacitor from the chassis to one or both sides of the AC line. You'll get a bit of a tingle if you get between it and something grounded (like antenna coax shield).

This doesn't indicate anything is wrong.

It's good practice to replace those line bypass capacitors with modern safety caps, since it they short it can become more dangerous.

frenchy
10-30-2010, 08:02 AM
Thanks, I'll see if I can locate the bypass caps and replace them, though if they are the paper/wax type I'm pretty sure I would have replaced them when I did the recap jobs.

miniman82
10-30-2010, 09:42 AM
The so-called 'death cap', right? Make sure you use X rated caps accross the line, Y rated when going from only one side to chassis. If you don't, there's a risk of the cap exploding.