Cable Auto-Detection (Toshiba 32AF33)
 

I have a Toshiba 32AF33 TV that I use in my living room, and it seems to have the ability to detect when an S-Video cable is plugged in to the Video 1 input, and it disables the Composite video input whenever this is the case. The S-Video cable does not have to be connected to a video source for the detection to work, as the Composite input gets disabled even when the other end of the S-Video cable is disconnected.

So I'm curious, how does the TV know when the S-Video cable is plugged in? I get how things like headphone jacks can work, since they can have that contact pair that breaks when the plug is inserted, but I'm just curious how a TV like mine would manage to pull that off with an S-Video jack.

The main reason I'm interested is because I'd kind of like to use a video switch box on this input, and I have a few that handle both Composite and S-Video, but in order to use a Composite device, I always have to reach around behind the TV and unplug the S-Video cable or else I get no picture. I think it would be neat if I could somehow switch out the S-Video input without actually unplugging the cable, perhaps by wiring up a switch that can disable the cable detection when I need it disabled, or something like that.

There is a switch built in to the jack. I think its
SPST so quick to defete BUT then the TV wont be looking
for S. It will always be looking for composite.............
Most likely switch goes right to a source switching IC.

73 Zeno:smoke:

What Zeno said.

I had a set once in my shop that insisted that something was plugged into the S video jack, when there was nothing. The switch in the jack was bad.

Had to order a new one from the manufacturer. It was crazy expensive at the time.

This was right after S-video came along on TV's.

Okay, I'll have to look at the PCB sometime and see if I can't intercept the traces coming from the switch.