Re: Question about scanning and "sync pulses"
Hi Chris,
In the UK, horizontal oscillators controlled by a DC voltage are known as 'Flywheel sync'. They were developed to cope with noisy or missing H sync pulses due to interference or poor reception. Manufactures sometimes offered a standard model for good signal areas, or a 'fringe' model for weak signal areas. These usually had flywheel sync and cost more to purchase.
The idea is that when running 'locked', the 'flywheel' action keeps the thing locked even if H sync pulses are not present for a few lines. Just like a physical flywheel.
The big, big downside is that they don't respond to rapid changes in timing of the sync. This was never a problem with broadcast TV, but when VCR's came along, some TV's took violent exception.
Due to the mechanical nature of VCR's, the timing of the H sync is all over the place. Because the flywheel can't respond rapidly enough, the result is anything from bent verticals at the top to the whole picture shaking like a jelly!!
There were many mods to try to get round this to enable a TV to be used with a VCR with varying levels of success.
I've never liked the DVD format and have a very soft spot for VCR and open reel video recorders. So on vintage Tv's, I like to use material on VHS played on early machines.
Trying to modify flywheel circuits to cope is usually fraught with problems!! A nice simple blocking oscillator is so much better!!
All the best
Nick
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