christmas balls - Videokarma.org TV - Video

Kiwick · #1 12-24-2008, 04:23 PM

do any of your TVs display a sort of christmas ball when turned off like my 1979 Philips does?

Here's the vid:
http://www.youtube.com/watch?v=NijEGMxUEOU

Blast · #2 12-24-2008, 08:11 PM

Almost like fireworks. My RCA CTC121 does something similar but yours is much more spectacular! With mine I was told it's a sign of a good CRT.

*zenithfan1* · #3 12-26-2008, 08:44 AM

Yes, I have several sets that do that, one is a CTC 121 and the other is a '68 Zenith console. The Zenith looks like the aurora borealis when it does it. I have a video, I will post it, looks very cool. That is a sign of a very strong CRT by the way, so it is good that your set does this.

drh4683 · #4 12-26-2008, 08:47 AM

This is unique, but I think 60's zenith color sets look by far the best when shut down. Its like looking into a kaleidoscope.

old_tv_nut · #5 12-26-2008, 04:41 PM

Turn-off behavior depends on how the various CRT voltages bleed down. Anything except a full-intensity focused spot is OK. One of the early black and white chassis designs at Motorola had a problem (fixed JUST before any were sold): The set had "instant-on" using a double-pole switch. It also had a video supply that came from the flyback and went only to the video output stage. When the set was turned off using the switch, everything was fine, but if you turned it off by pulling the plug, the CRT would get biased off, with no leakage path for the high voltage supply. Many seconds later, the video bias would finally bleed off, and because the cathode was still hot enough, the set would produce a very sharp very bright spot that would burn a hole in the phosphor in the center of the screen. This was discovered after the assembly line was started, when QC samples were taken out of boxes and the burned screens were discovered. Turns out the last part of production was to check out the set's operation, then pull the plug and box the set. The bright spot was occuring in the box. One of the engineers came up with a circuit using a reverse biased base-emitter junction of a transistor as a zener between B+ and the video supply. When the B+ fell, it pulled down the video supply also, and the CRT discharged while the raster was still collapsing.

A lot of sets I see today manage to discharge the CRT with a bright flash while the raster is shrinking but still quite large - no high voltage left to cause a lingering spot.

Blast · #6 12-26-2008, 05:30 PM

Hey, tv_nut, you've jogged the ol' memory. Funai had the same problem about 10-12 years ago and added a little circuit to eliminate, I believe, the same problem. Some Funai combos shut off with a 'design' that briefly looks like a sine wave on an oscilloscope turned up on it's side (ie: rotated 90 degrees). This may, or may, not be the aforementioned circuit in action.
Brian

old_tv_nut · #7 12-26-2008, 06:37 PM

Quote:

Originally Posted by Blast

Hey, tv_nut, you've jogged the ol' memory. Funai had the same problem about 10-12 years ago and added a little circuit to eliminate, I believe, the same problem. Some Funai combos shut off with a 'design' that briefly looks like a sine wave on an oscilloscope turned up on it's side (ie: rotated 90 degrees). This may, or may, not be the aforementioned circuit in action.
Brian

I've seen the occasional set that does that - the first time I saw it, I thought it was dangerously close to burning the screen if the raster had collapsed that far before the high voltage was discharged. Apparently it's not really a problem, as I've never seen one burned with that pattern - but it still startles me.