TV22 Scanlines - UK Vintage Radio Repair and Restoration Discussion Forum

Courtney Louise · 2nd Jun 2021, 6:19 pm

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

Heatercathodeshort · 2nd Jun 2021, 6:40 pm

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.

em536716 · 2nd Jun 2021, 7:15 pm

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

Courtney Louise · 2nd Jun 2021, 7:21 pm

Thanks guys, the sensitivity control and contrast work as they should. I will try a 1nf cap and John suggests

FRANK.C · 2nd Jun 2021, 8:06 pm

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

stacman · 2nd Jun 2021, 8:28 pm

N'mind the flyback lines, the 'ghostly' face in the screen in picture 1.....

Courtney Louise · 3rd Jun 2021, 9:10 am

Quote:

Originally Posted by stacman

N'mind the flyback lines, the 'ghostly' face in the screen in picture 1.....

Tell me about it, Been trying to get rid of that for ages, I assumed it was screen burn to start with

Helder Crespo · 4th Jun 2021, 10:21 am

Quote:

Originally Posted by Courtney Louise

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

Hi
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

Heatercathodeshort · 6th Jun 2021, 9:56 am

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.

Panrock · 7th Jun 2021, 8:20 am

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

Panrock · 7th Jun 2021, 3:01 pm

ppppenguin (Jeffrey) has written, assuring me that the Aurora is rock-solid in this respect and the Hedghog is likely to be too.

Steve

FRANK.C · 7th Jun 2021, 3:22 pm

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

2nd Jun 2021, 6:19 pm	#1
Courtney Louise Octode Join Date: Sep 2005 Location: Welshpool, Powys, Wales Posts: 1,327	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 Attached Thumbnails __________________ *33, 45, 78, around and around they go...*

2nd Jun 2021, 6:40 pm	#2
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	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
em536716 Hexode Join Date: Dec 2017 Location: South East London Posts: 301	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 __________________ With regards, Ed

2nd Jun 2021, 7:21 pm	#4
Courtney Louise Octode Join Date: Sep 2005 Location: Welshpool, Powys, Wales Posts: 1,327	Re: TV22 Scanlines Thanks guys, the sensitivity control and contrast work as they should. I will try a 1nf cap and John suggests __________________ *33, 45, 78, around and around they go...*

2nd Jun 2021, 8:06 pm	#5
FRANK.C Heptode Join Date: Feb 2006 Location: Roscommon, Ireland Posts: 732	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 __________________ www.electronics.frankcuffe.ovh

2nd Jun 2021, 8:28 pm	#6
stacman Hexode Join Date: Nov 2010 Location: Sheffield, South Yorkshire, UK. Posts: 278	Re: TV22 Scanlines N'mind the flyback lines, the 'ghostly' face in the screen in picture 1.....

6th Jun 2021, 9:56 am	#9
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	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
Panrock Nonode Join Date: Feb 2005 Location: Worcestershire, UK. Posts: 2,533	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 __________________ https://www.radiocraft.co.uk

7th Jun 2021, 3:01 pm	#11
Panrock Nonode Join Date: Feb 2005 Location: Worcestershire, UK. Posts: 2,533	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 __________________ https://www.radiocraft.co.uk

7th Jun 2021, 3:22 pm	#12
FRANK.C Heptode Join Date: Feb 2006 Location: Roscommon, Ireland Posts: 732	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 __________________ www.electronics.frankcuffe.ovh