"Flickering" analogue satellite picture

jamie1992

3 out of my 4 analogue satellite boxes (they're all quite old) have developed a strange fault whereby a horizontal band occupying approx the top 3rd of the picture has a 25Hz "flickering" effect when viewed on a CRT screen (it's totally not noticeable on an LCD screen). The 4th (and newest) receiver isn't affected (yet).
(Oddly, on CNN, the flickering band is towards the bottom of the screen instead!)

I asked about this on usenet, and it was suggested that the problem is being caused by a special energy dispersal waveform which is superimposed on the FM video carriers before transmission from the satellite to earth, in order to keep the carriers constantly modulated beyond a certain level, thereby preventing them from interfering with ground-based microwave uplinks.
Apparently the receivers' video clamping is supposed to filter it out, but when the clamping fails or deteriorates, the signal manifests itself as a flicker.

Can anyone here confirm this, and provide more information on how to solve the problem?

thanks,
jamie.

pedro2000uk

I would look for a fault on your equipment- even the CRT to make sure you do not have a fault causing high voltages on the low circuits- a/v /rf connectors etc.. Often a faulty power supply, failed capacitors &/or failed coil but it could be anything.

Certainly I would switch all off and soak test everything separately. Check for high voltages on the a/v connectors (scart & phono), aerial sockets etc.. with a meter. Test all on an RCD.

You could have one device that is faulty (crt?) and actually damaging others.

It may not be a fault on your equipment.... but that's what we would do first to rule a local fault out.