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Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
I recently took apart an old VCR to get the useful parts out. Whilst I had it in bits, I spotted this strange blue component on the pcb. It looked like it was a cover for something else, so I grabbed it and tried to pull it off. Suddenly glass shot everywhere and I was staring at this unsual frosted glass sheet with dark squares on it
Has anyone got any idea what this is? I haven't even got a clue, and I've not had any luck with google. Pic shows the cover on the left, and the remains of the (glass?) sheet attached to its wires.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
It's a delay-line. A piezo strip on one edge converts electrical signals to vibration (sound) that bounces all around the glass (you can easily trace the path - except when you've broken it ) The dark 'blobs' are obstacles to keep the 'beam' neat. A second piezo strip picks up the delayed signal. From memory
Registered Member #87
Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191
Boy, I remember i was looking at one of those in an old dead camcorder a few years back, puzzled me to no end! Anyone have any clue what the "dark blobs" are made of?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
It surely is a delay line. The PAL TV system used in Britain needs to compare the current scan line with the previous one as part of the demodulation process, so that delay line is needed to "remember" the previous line.
This clever system cancels out errors and gives better colour stability than the American NTSC system, which video guys jeeringly call "Never Twice the Same Colour" Of course, I guess it's done digitally nowadays.
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