ITT CVC9 text lines - UK Vintage Radio Repair and Restoration Discussion Forum

Welsh Anorak · 15th Mar 2007, 11:46 am

Hi all
It's quiet in the workshop so I'm renovating a CVC9 I've had for a while. Pictures are fair, but there are slight text lines at the top. As I'm lazy, I wondered if anyone had found a way of banishing them?
Should have some pictures of the set soon - I also need a front plastic panel - see the Wanted section.
Isn't it funny how faults that used to drive us mad when the sets were current are quaint and nostalgic now?
Glyn

Hunts smoothing bomb · 15th Mar 2007, 11:55 am

Hello Glyn,

My K70 I use also suffers with text lines at the top of the picture which isn't a problem during bright seens but dark scenes, well...... forget it, it's unwatchable.
I cured them by buying a cheap modulator from maplins which has an output variable from CH21-69 UHF.

Works a treat for me.

Cheers
Lee

Focus Diode · 15th Mar 2007, 11:56 am

I used Freeview to eliminate the problem. Lines are still apparent on Macrovision protected VHS or DVD material however. Thankfully Macrovision is now old hat, thus unlikely to be seen on newer releases.

Worth noting mods for VCR use which works very well: Change C288 to 820pF, C290 to 0.1uF and R395 to 47K.

Cheers,
Brian

Nickthedentist · 15th Mar 2007, 12:04 pm

Didn't Darius design a simple, universal circuit to help with this problem?

See here: https://www.vintage-radio.net/forum/...+flyback+lines

dazzlevision · 15th Mar 2007, 6:25 pm

Hi,

IIRC, there was an official ITT mod, consisting of a monostable multivibrator circuit, on a small PCB, which stretched the field flyback blanking pulse. This was enough to blank out the number of Teletext lines occupying the vertical blanking interval - in those days.

ISTR there was an article in "Television" magazine, which covered Teletext interference blanking - including this circuit - probably circa 1980.

Regards,

Dazzlevision

Welsh Anorak · 16th Mar 2007, 2:10 pm

Hi all
Thanks for the info! I think Darius's circuit is a bit over the top for such a recent (!) set - Dazzlevision's is the one I was thinking of. Now all I need to do is unearth my pre-1981 magazines! However, I wonder if it will be enough for the increased number of lines - I might just use a modulator as suggested. In fact, they aren't too bad at all.
Now I need to get going on the cabinet!

Glyn

Hybrid tellies · 16th Mar 2007, 9:58 pm

I had this problem on my Decca Bradford; I got rid of them when I did a full convergence set-up after the last tube replacement (back in the early 90's).
Strangely enough it was changing the parabola shape (flying lead on the convergence board) then resetting the convergence and frame linearity controls which finally cleared the problem.
I guess it must have had some effect on the flyback speed, so it might be an idea to check any components around the primary winding of the frame output transformer, such as caps feeding off the anode of the pentode section of the PCL805 back into the linearity network.

oldeurope · 17th Mar 2007, 5:09 pm

Quote:

Originally Posted by Nickthedentist

Didn't Darius design a simple, universal circuit to help with this problem?

See here: https://www.vintage-radio.net/forum/...+flyback+lines

Yes.
http://bs.cyty.com/menschen/e-etzold.../uvb/uvb_e.htm

Kind regards,
Darius

15th Mar 2007, 11:46 am	#1
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,921	ITT CVC9 text lines Hi all It's quiet in the workshop so I'm renovating a CVC9 I've had for a while. Pictures are fair, but there are slight text lines at the top. As I'm lazy, I wondered if anyone had found a way of banishing them? Should have some pictures of the set soon - I also need a front plastic panel - see the Wanted section. Isn't it funny how faults that used to drive us mad when the sets were current are quaint and nostalgic now? Glyn

15th Mar 2007, 11:55 am	#2
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	Re: ITT CVC9 text lines Hello Glyn, My K70 I use also suffers with text lines at the top of the picture which isn't a problem during bright seens but dark scenes, well...... forget it, it's unwatchable. I cured them by buying a cheap modulator from maplins which has an output variable from CH21-69 UHF. Works a treat for me. Cheers Lee __________________ Lee

15th Mar 2007, 11:56 am	#3
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: ITT CVC9 text lines I used Freeview to eliminate the problem. Lines are still apparent on Macrovision protected VHS or DVD material however. Thankfully Macrovision is now old hat, thus unlikely to be seen on newer releases. Worth noting mods for VCR use which works very well: Change C288 to 820pF, C290 to 0.1uF and R395 to 47K. Cheers, Brian

15th Mar 2007, 12:04 pm	#4
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,846	Re: ITT CVC9 text lines Didn't Darius design a simple, universal circuit to help with this problem? See here: https://www.vintage-radio.net/forum/...+flyback+lines

15th Mar 2007, 6:25 pm	#5
dazzlevision Dekatron Join Date: Sep 2003 Location: Near Swindon, North Wiltshire, UK. Posts: 3,612	Re: ITT CVC9 text lines Hi, IIRC, there was an official ITT mod, consisting of a monostable multivibrator circuit, on a small PCB, which stretched the field flyback blanking pulse. This was enough to blank out the number of Teletext lines occupying the vertical blanking interval - in those days. ISTR there was an article in "Television" magazine, which covered Teletext interference blanking - including this circuit - probably circa 1980. Regards, Dazzlevision

16th Mar 2007, 2:10 pm	#6
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,921	Re: ITT CVC9 text lines Hi all Thanks for the info! I think Darius's circuit is a bit over the top for such a recent (!) set - Dazzlevision's is the one I was thinking of. Now all I need to do is unearth my pre-1981 magazines! However, I wonder if it will be enough for the increased number of lines - I might just use a modulator as suggested. In fact, they aren't too bad at all. Now I need to get going on the cabinet! Glyn

16th Mar 2007, 9:58 pm	#7
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,965	Re: ITT CVC9 text lines I had this problem on my Decca Bradford; I got rid of them when I did a full convergence set-up after the last tube replacement (back in the early 90's). Strangely enough it was changing the parabola shape (flying lead on the convergence board) then resetting the convergence and frame linearity controls which finally cleared the problem. I guess it must have had some effect on the flyback speed, so it might be an idea to check any components around the primary winding of the frame output transformer, such as caps feeding off the anode of the pentode section of the PCL805 back into the linearity network. __________________ Simon BVWS member Last edited by Mike Phelan; 21st Dec 2007 at 11:23 am. Reason: S&P