Question about static shock protection of audio/video inputs

[mndflmr]

Hi all,
I have a Philips TV/VCR combo that was recently damaged when I
attempted to hook up a VCR to the RCA input jacks. A static spark on
the video input damaged the IC that deals with the color component of
the video signal. I managed to replace the IC, restoring color to the
VCR portion of the TV (the off-air signal was not affected). This
repair also restored the video input capability, which had been lost.
Now for my question: What can I do to protect the audio/video inputs
against static discharge? Would it be as simple as adding some
component to the + inputs, such as a capacitor or a resistor or
something? Any advice would be greatly appreciated. It was no fun
replacing the 100-pin surface mounted IC and I hope to avoid having to
do it again!
Joe

 

[Jerry G.]

A very crude way to have some protection is to first ground the shield part
of the connector to the ground of the TV set that is to be inserted to the
TV's input jack before inserting it. This would be the same for both the
audio and the video.

There is an old trick that may work, and it will not effect the performance
of the devices. There is a small neon lamp called an NE-2 with 2 inch leads
on it. This lamp will fire up at about 65 Volts. At this voltage it becomes
very conductive. It is very sensitive, and it will fire up on static
discharge. The input side of your TV set will most likely be able to take a
short burst of the 65 Volts on its input at the very low current level that
static electricity will deliver. On the inside of your TV's connector for
each of the video inputs, and outputs, solder one of these neon tubes across
(parallel) between the conductor side, and the ground.

This is an old trick that was used in some commutations receivers to protect
the front end RF transistor that is on the antenna input. I read an article
about this approach in one of the many electronics magazines that I used to
subscribe to.

There are input device protection circuits that are much more complex than
the solution that I described. Care must be taken to not change the
characteristics of the input signal to your TV set, thus degrading the sound
and picture quality.

Input device protection description:
www.fairchildsemi.com/an/AN/AN-248.pdf

Detailed research article about static protection:
http://www.static-planet.com/pdfs/fund_req.pdf

 

[mndflmr]

Thank you Jerry,
I like the simplicity of your suggestion. I was hoping there was a
simple solution and it seems like this will do what I was asking.
Also thanks for the intersting links. I have learned some things
after just glancing at the files. Later on I will spend more time
reading them. Thanks again.

Joe

 

[Jerry G.]

Proper static protection by far is not a simple task.