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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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2nd Jun 2021, 6:19 pm | #1 |
Octode
Join Date: Sep 2005
Location: Welshpool, Powys, Wales
Posts: 1,327
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TV22 Scanlines
Hi all.
After checking all caps and stuff I can’t get the brightness to zero or to get rid of these scan lines. I have adjusted the capacitor under the chassis to eliminate the vertical stripe. Any hints? Cheers C
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33, 45, 78, around and around they go...
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2nd Jun 2021, 6:40 pm | #2 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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Re: TV22 Scanlines
You need to fit frame flyback suppression.
The easiest was is to wire a small capacitor say 1000pf between the anode of the frame output valve and grid of the CRT. There are slightly different variations of the circuit. J. |
2nd Jun 2021, 7:15 pm | #3 |
Hexode
Join Date: Dec 2017
Location: South East London
Posts: 301
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Re: TV22 Scanlines
I think the brightness issue might be due to a strong signal being applied. What happens when you adjust the sensitivity control?
As mentioned These need a mod to dampen the fly back lines
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With regards, Ed |
2nd Jun 2021, 7:21 pm | #4 |
Octode
Join Date: Sep 2005
Location: Welshpool, Powys, Wales
Posts: 1,327
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Re: TV22 Scanlines
Thanks guys, the sensitivity control and contrast work as they should. I will try a 1nf cap and John suggests
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33, 45, 78, around and around they go...
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2nd Jun 2021, 8:06 pm | #5 |
Heptode
Join Date: Feb 2006
Location: Roscommon, Ireland
Posts: 732
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Re: TV22 Scanlines
Hi Courtney
If you turn on "Pedestal" on your Hedghog it may help a little. As it raises black level about 5% above blanking level. Frank
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2nd Jun 2021, 8:28 pm | #6 |
Hexode
Join Date: Nov 2010
Location: Sheffield, South Yorkshire, UK.
Posts: 278
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Re: TV22 Scanlines
N'mind the flyback lines, the 'ghostly' face in the screen in picture 1.....
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3rd Jun 2021, 9:10 am | #7 |
Octode
Join Date: Sep 2005
Location: Welshpool, Powys, Wales
Posts: 1,327
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Re: TV22 Scanlines
Tell me about it, Been trying to get rid of that for ages, I assumed it was screen burn to start with
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33, 45, 78, around and around they go...
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4th Jun 2021, 10:21 am | #8 | |
Hexode
Join Date: Sep 2019
Location: Crystal Palace, Bromley, London, UK.
Posts: 417
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Re: TV22 Scanlines
Quote:
I have performed this simple mod in my TV22 Mk2, which has resulted in improved reduction in flyback lines (in fact, they don't show at all when contrast and brightness are properly set): https://www.vintage-radio.net/forum/...ad.php?t=20539 Helder |
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6th Jun 2021, 9:56 am | #9 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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Re: TV22 Scanlines
An increasing problem that I am finding with these early Mullard tubes is internal leakage.
With the grid volts at zero [brightness control at minimum] the screen should be blanked out. You could try rewiring the base as a triode but you will find that the drive is reduced giving a picture with a lot less 'punch'. J. |
7th Jun 2021, 8:20 am | #10 |
Nonode
Join Date: Feb 2005
Location: Worcestershire, UK.
Posts: 2,533
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Re: TV22 Scanlines
I think I heard somewhere that the situation improves when the sync bottoms are properly clamped to near-zero carrier out of the modulator, regardless of picture content. Maybe the Aurora and Hedghog allow the DC reference to vary with picture content slightly? I haven't checked this.
Steve
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7th Jun 2021, 3:01 pm | #11 |
Nonode
Join Date: Feb 2005
Location: Worcestershire, UK.
Posts: 2,533
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Re: TV22 Scanlines
ppppenguin (Jeffrey) has written, assuring me that the Aurora is rock-solid in this respect and the Hedghog is likely to be too.
Steve
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7th Jun 2021, 3:22 pm | #12 |
Heptode
Join Date: Feb 2006
Location: Roscommon, Ireland
Posts: 732
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Re: TV22 Scanlines
Hi Steve
All the Hedghog's use the MC44BS373CA Modulator. It's data sheet can be downloaded from https://www.mouser.ie/ProductDetail/...QpY1Rw8dowZA== Within the modulator the sync tips are clamped. So I would expect black level to be stable regardless of picture content. I can only speak for the Hedghog but as the Aurora uses the same modulator I cant see it being any different. Frank
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