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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Mar Wed 27, 2019 1:57 pm 
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Joined: Mar Sat 09, 2019 12:59 pm
Posts: 1
I saw on the schematic that there is a TV/Phono switch. Your specific unit probably won't have the switch, yet it would appear that on the off chance that it is set to Phono, news at that point it slices the fiber voltage to the CRT. Have you watched that switch?


Last edited by LyndonWynn on Apr Tue 02, 2019 11:27 am, edited 1 time in total.

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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Mar Wed 27, 2019 7:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 5414
Location: Woodinville, WA USA
What is “fiber voltage?”

Phil Nelson


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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Mar Thu 28, 2019 8:12 pm 
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Location: Dallas, TX
philsoldradios wrote:
What is “fiber voltage?”

Phil Nelson

He probably means "filament". Maybe English isn't his native language.

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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Mar Thu 28, 2019 8:37 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 3484
Location: Dallas, TX
I wanted to show the OP why getting that Velleman K8025 video generator might be useful.
It has a staircase or grey scale mode. This is what a line of video looks like on a scope.
Attachment:
ScopeStaircaseE1.jpg
ScopeStaircaseE1.jpg [ 153.12 KiB | Viewed 1291 times ]

It is a stable pattern that is easier to see on a scope. The time between horizontal sync pulses
is 63.5 uS, from the 15735 Hz horizontal frequency. You also know the signal reaches the
white level so that the peak-to-peak measurement will be accurate.
If you set your scope to a slower rate, the video frames look like this.
Attachment:
ScopeStaircaseE2.jpg
ScopeStaircaseE2.jpg [ 151.45 KiB | Viewed 1291 times ]

The times between half frames is 16.6 mS, from the 60 Hz vertical frequency. The staircases are
compressed together so they overlap. You can see that just from changing the scope settings
that the scope display is very different. The trigger controls as well as the horizontal time
setting on the scope were changed.
This is what a staircase looks like on the TV screen.
Attachment:
ScreenStaircaseE1.jpg
ScreenStaircaseE1.jpg [ 114.9 KiB | Viewed 1291 times ]

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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Mar Fri 29, 2019 1:28 am 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
Thanks Mark.
Those pictures were taken of signals coming from a Sencore unit, I don't have the Velleman
generator. I didn't know the Velleman unit existed until this week, it probably doesn't make
as sharp a signal as the Sencore.
I found the Velleman unit while googling for a DVD test disc. I got this DVD several years ago.
Attachment:
VideoTestDiscE1.jpg
VideoTestDiscE1.jpg [ 148.56 KiB | Viewed 1277 times ]

That company (Electronix Corp.) is out of business. Similar DVD might be available but they seem
more pricey than what I remember paying. I think there is a way of making your own DVD starting
with patterns created on Photoshop or similar.
Since most if not all DVD players do not have a RF output you still need a RF modulator.
One drawback of the DVD method is that it tests the DVD player as much as the TV.

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