Bypassing tuner in Zenih Chromacolor?

[vinyldavid]

As I have posted before, I have an old Zenith chromacolor TV that has a dirty mechanical tuner.

Since we are 'apparently' switching to digital sometime soon, I figure it would be better to just bypass the tuner and somehow put a composite or S-Video input on the back of it, as I am only going to be using it as a screen.

SO is there any way to do this? The tuner itself is really dirty...

[jfrog1983]

I would also like to do the same with my Chromacolor, basically have at least a composite video input that bypasses the tuner. The tuner has it's share of problems, and it would be nice to hook DVD players and the like to my Chromacolor.

[Eric H]

Shooting a little Deoxit into the tuner will likely cure it, at least well enough to use channel 3 or 4 which is all you'll need after the switch.

[zenith2134]

It might not be so easy to bypass the tv's tuner. First off, that set might have a floating ground/hot chassis in which case you'd need to isolate the Composite input's shield from the TV chassis. Second, you might need a schematic to find the proper point to insert the audio/video signal, then gotta get the sync right.

[old_tv_nut]

I'd second the warning about making sure the chassis is not hot. I'd also note that many sets used at least a 2 volt detector output, so you need some amplification for the usual 1 volt video input. Maybe not impossible, but needs a little study.

[wa2ise]

Originally Posted by old_tv_nut

I'd also note that many sets used at least a 2 volt detector output, so you need some amplification for the usual 1 volt video input. Maybe not impossible, but needs a little study.

If you have S video from the DTV converter or DVD player, you could feed the luma and the chroma of the S video downstream of the chroma-luma separation circuit. That's usually a low pass filter for the luma, and a bandpass for teh chroma. Disconnect those, and feed the amplified (if necessary) luma and chroma signals. Be careful that the luma signal is phased correctly as needed, the chroma signal is less fussy. The sync separator will also need to be fed by the luma signal.

[vinyldavid]

I could have a ch 3/4 output from a VCR or DTV converter box, and if I could somehow just feed that directly in, that would be good, too...

[basil lambri]

If you want to feed composite input to that TV what you need is an RF modulator. You can get one from Radio Shack for example. You connect the composite cables coming from the DTV converter or cable box or VCR to the RF modulator and then you connect the modulator to the TV with a 75 Ohm coaxial cable. You might need an additional 75 to 300 Ohm (twin lead) converter because it is an old TV. The modulator feeds the TV on channel 3 or 4.

[vinyldavid]

Originally Posted by basil lambri

If you want to feed composite input to that TV what you need is an RF modulator. You can get one from Radio Shack for example. You connect the composite cables coming from the DTV converter or cable box or VCR to the RF modulator and then you connect the modulator to the TV with a 75 Ohm coaxial cable. You might need an additional 75 to 300 Ohm (twin lead) converter because it is an old TV. The modulator feeds the TV on channel 3 or 4.

Right. But the tuner inside of the TV is pretty dirty and drifty, and I am trying to bypass it, to have a direct composite input to the TV.

[vinyldavid]

Next time I go to my grandmother's house for a few hours, I'll pull it apart and have a look....