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  #1  
Old 12-11-2017, 07:39 PM
mbates14 mbates14 is offline
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Motorola VT-71 Composite/s-video in?

In a ditch effort to get my VT-71 back into full operation again, instead of using the tuner and attempting an IF alignment which uses gear I do not own, has anyone attempted to modify the set to allow a composite/audio input?

Audio is fairly easy and straight forward. But the video side, I am not sure. I was thinking about using A/V extenders. Put one at the DirecTV box, and the toher one at the TV. it has S-Video which is nice because I could get rid of the chroma signal, stick strictly with luma.

Problem is, Not sure where to inject that signal, its not as straight forward. Detector diode? would it be strong enough? or would I need serious modifications?
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Old 12-11-2017, 08:03 PM
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Inject your composite source to pin one of the video amp tube (make sure to disconnect existing connections going to pin 1 first!). Make sure to add a .1uf say 630v cap in series to isolate from any dc feedback. Then of course connect the shield of the wire to ground!
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Old 12-11-2017, 08:22 PM
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Electronic M Electronic M is offline
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First off if you don't have a line isolation transformer to power the VT-71 with, don't try this...If you connect a hot chassis set to a grounded chassis video source something WILL be damaged.

The detector diode probably is your best bet for an injection point. If polarity or amplitude is wrong an OP-AMP circuit can be made to deal with that.

Personally, unless you know that the tuner or if is badly damaged, I recommend just trying the tuner and IF circuits after a recap and seeing how they do...Most sets don't NEED an alignment to work decently. Bear in mind the detector diode and video peaking coils in these can fail and give odd symptoms that look like alignment issues.
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Old 12-12-2017, 09:34 AM
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bandersen bandersen is offline
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The VT-71 B- bus is routed underneath the chassis and isolated. The chassis is floating and can be grounded safely.
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Old 12-12-2017, 09:45 AM
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One of my vt71 sets I used the ant wire to the 1n34 and got sound and pic but it's been fixed since and don't remember why I did it to begin with.
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  #6  
Old 12-20-2017, 08:04 PM
mbates14 mbates14 is offline
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The tuner works but the alignment and audio buzz is definitely off. it needs an alignment with gear that I dont own. This is the only vintage set I own now actually. I used to have a ton of gear and quite a few vintage sets, but unfortunate circumstances happened within the last 10 to 12 years which changed that.

The last time I had touched/restored this set was 2004 or thereabouts, I may even have a thread on it here in this forum somewhere. Same set. I was 18 at the time. I am 32 now and been through 1 major theft instance, and 3 moves. Wow time flies...

Plus these days, modulators and anything RF/Cable related is getting harder and harder to find that connect to modern standards. I have a DirecTV box that has only HDMI and a special proprietary plug to get standard A/V. But no RF anymore. Genie model I think?

My thought is use those little Audio/Video extenders that radio shack used to sell, I have a set. they have S-Video as well, so that gives me an opportunity to get the luminance signal and not have the chroma dot-crawl on a B&W Set. Hook one at the DTV box using the A/V out, and hook the other at the TV.

Anyways, OTA is out because I live in the mountains and there is only 1 station that is receivable currently. The cable system finally switched over to all digital and encryption, the DTA adapters are not available, can only get the full size box. But I already have DTV so that doesnt matter.

These days as an embedded developer and software programmer, I thought about setting up a Raspberry Pi as a media server and player that has all my old shows and programs on it, and then I can let it roll on the TV, All self-contained. :-) I might cheap out and use XBMC/Kodi here, or write something myself. Havent decided yet. If I do go that route, then I will add a power circuit so the Pi can turn the TV on and off. So when I shut down the media software, it will turn off the TV :-)

Last edited by mbates14; 12-20-2017 at 08:13 PM.
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  #7  
Old 12-20-2017, 09:51 PM
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This might be what you are looking for;
https://www.ebay.com/itm/Digital-ATS...EAAOSwnVhaOkLx

I have two of these & these were the easiest solution i found so far as to play the classic tv shows that i downloaded from you-tube & other classic tv sites on my vintage tv's. this device plays back mp4 files flawlessly. the tuner part is not that great. it does have a composite A/V output as well as channel 3/4 rf out. best of all, it's cheap. it will play 4.3 content as 4.3 (full screen).
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  #8  
Old 12-21-2017, 01:49 AM
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David Roper David Roper is offline
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I find that depends entirely on who uploaded content and how. YouTube content is usually shrunken somehow, most often at the right hand side of the screen (dark bar appears).
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