Help required with club televisor

Forum for discussion of narrow-bandwidth mechanical television

Moderators: Steve Anderson, Dave Moll, Andrew Davie

Help required with club televisor

Postby G8VPG » Tue Sep 10, 2013 9:37 pm

I have been struggling to get the motor speed control correct with the standard club televisor board. I have followed Karen's advice in the last newsletter, and unplugged the 4046 and am able to get the motor free running and display drifting pictures. Today I got the 'scope out and the problem seems to be with the sync separator. At very low video drive levels, 100mV peak to peak, I get a nice clean sync pulse at pin 7 of ic1b. As soon as I increase this, I get multiple spurious sync pulses, which causes the 4046 to overspeed the motor. Any suggestions would be very welcome!
Kind regards, Shaun.
G8VPG
"Fester, enough of the light-bulbs!"
 
Posts: 3
Joined: Tue Sep 10, 2013 8:38 pm
Location: Bristol

Postby Klaas Robers » Wed Sep 11, 2013 12:52 am

I think it very likely that your problem is the video signal, rather than the sync separator.

What is your signal source? How are the video signals when you look at them on your oscilloscope, especially the sync pulses in the video signal as they come from your signal source / CD-player? If yours has tone controls, adjust them until the signal is nice and clear. A flat characteristic is needed.
User avatar
Klaas Robers
Frankenstein was my uncle.
 
Posts: 1498
Joined: Wed Jan 24, 2007 8:42 pm
Location: Valkenswaard, the Netherlands

Postby G8VPG » Wed Sep 11, 2013 6:07 am

Thank you for your advice Klaas,
The source is a club CD played on a DVD/CD player with line level output and no tone controls. I will try another player that I have and see if it makes a difference.
Kind regards, Shaun.
G8VPG
"Fester, enough of the light-bulbs!"
 
Posts: 3
Joined: Tue Sep 10, 2013 8:38 pm
Location: Bristol

Postby Klaas Robers » Thu Sep 12, 2013 1:15 am

First look at the video signal (left channel out) of your player. You will recognise the sync pulses, they should be negative and the most negative levels should have an almost constant level, not really waving. The line output is the most undistorted signal that you can get. The peak to peak voltage should be about 1 to 1.5 volts.

Then try to synchronise you oscilloscope to the signal half way the sync. In this way you can get an impression of the quality of he video signal. If that is good and the monitor still doesn't synchronise, something is not properly working in the sync separator. But in most cases you will see it already on the video signal.

Look at http://www.nbtv.wyenet.co.uk/sound.htm to see how the video signal should look like. This is what really IS on the CD
User avatar
Klaas Robers
Frankenstein was my uncle.
 
Posts: 1498
Joined: Wed Jan 24, 2007 8:42 pm
Location: Valkenswaard, the Netherlands

Postby G8VPG » Thu Sep 12, 2013 4:31 am

Thank you Klaas,
I will do this and report back. Kind regards, Shaun.
G8VPG
"Fester, enough of the light-bulbs!"
 
Posts: 3
Joined: Tue Sep 10, 2013 8:38 pm
Location: Bristol


Return to Mechanical NBTV

Who is online

Users browsing this forum: No registered users and 5 guests

cron