malfunctioning teletext

[Kiwick]

Hi you all.

I have a malfunctioning teletext decoder on my latest curb find, a 1985 Philips K40, even with a clean, strong signal, it displays a lot of corrupt characters and it often fails to stop at the selected page,

Any thoughts on what might be going wrong?

[wa2ise]

IIRC (If I recall correctly), teletext has no error correction capability, so even some noise or interference will screw it up.

[larschr]

I had a similar problen once. The TXT acted up and "locked" itself at last. When i replaced the TXT card, the problem was gone.

[dr.ido]

From memory some early teletext cards used 2102 or 2114 SRAMs. These SRAMs are prone to failiure. I've never replaced one in a TV (most people don't use teletext and aren't willing to pay for it to be repaired as long as the rest of the set is working), but I've replaced many in various vintage computers where they were often used as video RAM and their failure will cause a corrupted display.

It's been a long time so my memory may be way off.

[old_tv_nut]

Who is broadcasting teletext these days? I thought it died out long ago.

[dr.ido]

All analog channels here except C31 (community channel) broadcast teletext. ABC, 9 and 10 only use it for subtitles. Channel 7 has news/information/TV guide pages as well as subtitles. I've only ever seen test patterns on SBS's signal, but I haven't checked it recently.

Channel 7's teletext pages are mirrored on their digital signal, but I don't think anyone else has teletext on their digital channels.

I think the TAB still uses teletext on their satellite racing channels for race information. If it's no longer an actual teletext signal it has been designed to look exactly like the old teletext pages.

Teletext was used heavily enough here in some niche areas that several companies made teletext adapters/cards for various computers. I have a teletext decoder on an 8 bit ISA card (it's not a TV tuner, it can only decode teletext from a composite video signal) that came with software to scrape race results into a CSV file.

[Kiwick]

Originally Posted by old_tv_nut

Who is broadcasting teletext these days? I thought it died out long ago.

Here in Europe, virtually every TV channel comes with Teletext... if you're watching early B/W tube sets here you have to live with teletext data showing in the retrace lines.

[wa2ise]

Back in the 80s when I used to work for the old RCA Smirnoff labs in Princeton NJ, I suggested as a patent having a home computer generate a teletext signal to insert on the approprate line in the computer video to create computer text and graphics (what little teletext could support). And the TV set in teletext mode would present a nice sharp and clear readout of the computer, instead of the usually blurry analog RF modulated image you usually had back then.

Didn't go anywhere....

[dr.ido]

I doubt most TV's (even those with FastText) could update such a display quick enough for it to be viable for general computer use.

The BBC Micro has a teletext chipset built in and used it for it's "mode 7" display. External teletext decoders were available and BBC software was distributed over teletext for a while.

[bgadow]

Wow-it's like you guys are in a whole 'nother country or something !