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 Post subject: Possible cure for retrace lines on Motorola VT-71, VT-73
PostPosted: Aug Tue 03, 2004 6:45 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1643
Location: Burbank, CA and Thailand
This is something that's bothered me on my Motorola sets, others have also mentioned it. A friend gave me an idea for a possible fix and it seems to work.<P>His advice was: "Motorola made changes in their 9T1 set that fixed this problem. Look at how they wired the first CRT grid on that set and try doing the same thing on a VT-71".<P>The circuit change turns out to be simple. On the VT-71 and VT-73 (and perhaps other early Motorolas) there is a 250 pf capacitor (C139) between pin 5 of the 6SL7 vertical sweep output tube and ground. Lift the lead going to ground and install a 220k resistor between that lead and ground.<P>Then, locate the the wire that goes from pin 3 of the CRT to ground. Disconnect it from ground and connect it to the junction of the the 250pf cap and the new 220k resistor.<P>The new RC circuit creates a brief -4 VDC pulse during the retrace, which cuts off the CRT and blanks the retrace lines.<P>It seems to work great, and even blanks the really nasty lines that appear when playing some DVD's. Perhaps someone else with one of these sets can give it a try and report back; I hope the success I had with the set now on my bench was not just a fluke.<P>P.S. I added a reply with other details about this to mark fitzgerald's macrovision thread, where the problem of diagonal lines was discussed recently.<BR>------------------


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 Post subject: Possible cure for retrace lines on Motorola VT-71, VT-73
PostPosted: Dec Sat 03, 2005 1:42 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2151
Location: Waukegan, IL
Ok, I tried David's mod and it does eliminate retrace lines. But, after the set is on for some time, I start to get jitters in the vertical. I never had them before. I need some expert advise from someone who really knows these tv's and circuit. Do you think changing the value of the resistor or cap may eliminate the jitters? Or maybe some other compnent in the vertical section is to blame?<P>------------------<BR>Tony


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 Post subject: Possible cure for retrace lines on Motorola VT-71, VT-73
PostPosted: Dec Sat 03, 2005 3:37 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1796
Location: Phoenix, Arizona
Macrovision . . . That hit a nerve here.<P>First;<P>Part of the problem may be Vertical Interval Test Signals (VIT's) broadcast by your local station and or Closed Caption.<P>The Vit's usually contain full video level signals like color bars. Usually they are on lines around 17 in the vertical blanking, with Closed Caption on 21. <P>Macrovision is a particularly nasty problem as it's generated IN YOUR DVD player. Some early players had a secret menu which allowed it to be switched off. A couple of lawsuits took care of that. <P>The Macrovision annoyance signal uses pulsating video signals through the entire vertical interval that exceed NTSC specifications.<P>Most TV sets and particularly high end tube projection sets go nuts when Macrovision intrudes. They of course deny this. <P>When you can rent a movie on a DVD for a couple of bucks I can’t understand why anyone would buy a blank tape and try to rip off a movie in the first place.<P>When you buy a retail movie you pay about $2.00 to the Macrovision lawyers for their lovely service.<P>Unfortunately I don't offer a cure, I have had more trouble with this in Predicta’s. I feel much better now that I got to rant about Macrovision.<BR><P>------------------<BR>


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 Post subject: Possible cure for retrace lines on Motorola VT-71, VT-73
PostPosted: Dec Sat 03, 2005 10:16 am 
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Location: San Jose, CA USA
I've implemented David's fix on three different electrostatic sets and have been very pleased with the improvement. You do have to fiddle a bit with the R and C values in different sets, but once things are set, I haven't seen it cause any problems with the vertical sync.<P>Tom<P>------------------<BR>


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 Post subject:
PostPosted: Dec Mon 20, 2010 12:27 pm 
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Joined: Dec Mon 20, 2010 12:21 pm
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Appreciate the info, it’s good to know.

Motorola Pakistan


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 Post subject:
PostPosted: Jan Thu 06, 2011 5:14 am 
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Joined: Dec Sun 02, 2007 4:54 am
Posts: 163
Location: Columbia, MO
could someone out there look at a schematic for this set or the teletone tv220 and give advise from there? I have looked at the motorola schematic as well as the TV 149, And I'm just not sure what to do. I know its simple but I just can't seem to wrap my brain around it.

And yes that is Dennis Weaver in Duel. Good eye.

Thanks again, Sean.


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