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 Post subject: Picture shrinks as tv warms up
PostPosted: Jan Sun 07, 2018 4:02 am 
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Joined: Sep Sat 12, 2015 10:13 pm
Posts: 66
Location: Knoxville, Tn
I have a motorola vt-73 with the ts-4j chassis, and i have replaced all the capacitors and a few of the resistors, and the picture takes up the whole screen at first, but then it shrinks and is really small. Also, there is no sound at all, even when i first turn on the tv. Any help is appreciated!


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 Post subject: Re: Picture shrinks as tv warms up
PostPosted: Jan Sun 07, 2018 4:27 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 355
In which direction does it shrink? Horizontally, vertically or both?
How long does it take for this to happen?


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 Post subject: Re: Picture shrinks as tv warms up
PostPosted: Jan Sun 07, 2018 4:52 am 
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Joined: Sep Sat 12, 2015 10:13 pm
Posts: 66
Location: Knoxville, Tn
irob2345 wrote:
In which direction does it shrink? Horizontally, vertically or both?
How long does it take for this to happen?

It shrinks vertically for the most part. It takes about 5-10 minutes for this to happen


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 Post subject: Re: Picture shrinks as tv warms up
PostPosted: Jan Sun 07, 2018 6:38 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 355
Does it shrink horizontally at all at the same time?

I'm in Australia, If you post a link to the circuit I'll have a look.


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 Post subject: Re: Picture shrinks as tv warms up
PostPosted: Jan Sun 07, 2018 4:59 pm 
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Joined: Jan Sat 16, 2016 10:03 pm
Posts: 370
try swapping-out the vertical output tube with a known good one.


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 Post subject: Re: Picture shrinks as tv warms up
PostPosted: Jan Sun 07, 2018 7:35 pm 
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Joined: Sep Tue 15, 2015 9:25 pm
Posts: 245
Quite agree. Swap out the vertical output tube as it may be gassy. If both vertical and horizontal are shrinking you may want to look into HV increasing as the set warms internally.


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 Post subject: Re: Picture shrinks as tv warms up
PostPosted: Jan Sun 07, 2018 9:16 pm 
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Joined: Sep Sat 12, 2015 10:13 pm
Posts: 66
Location: Knoxville, Tn
Reichsrundfunk wrote:
Quite agree. Swap out the vertical output tube as it may be gassy. If both vertical and horizontal are shrinking you may want to look into HV increasing as the set warms internally.

So swap both 12sn7gt tubes?


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 Post subject: Re: Picture shrinks as tv warms up
PostPosted: Jan Sun 07, 2018 9:26 pm 
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Joined: May Fri 29, 2009 4:35 am
Posts: 2057
Location: Chicago, IL USA
The vertical output tube is the 6SL7. The vertical circuit is a little tricky because the plate voltage comes from the HV power supply through a voltage divider made from a bunch of high valued resistors. Those resistors sometimes act weird after years of high voltage on them. Like the resistance changes as the set runs. I've seen arcing in the 6SL7 base too.


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 Post subject: Re: Picture shrinks as tv warms up
PostPosted: Jan Tue 09, 2018 9:11 pm 
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Joined: Nov Thu 11, 2010 6:03 pm
Posts: 674
Location: Pewaukee, WI
Cases like these are often original resistors drifting high in value as they warm. Get a can of freeze spray, canned air or the like that will cool what is sprayed. Once the set warms up to the point that it starts noticeably shrinking with the set running hit sections of the vertical and what feeds it with the spray and look for an increase in height. Once you know the area focus on individual parts till you find the culprit(s).


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