[Coco] FM-77AV video sync problems
KnudsenMJ at aol.com
KnudsenMJ at aol.com
Tue Apr 11 22:57:58 EDT 2006
In a message dated 4/11/06 10:24:35 PM Eastern Daylight Time,
yahoo at dvdplayersonly.com writes:
> I am confused about the power line frequency and how it relates to
>television. All the TVs I've worked on convert the incoming AC power to DC,
>switch it to AC(almost), goes through a transformer at a high
>frequency(efficiency), and then converts it back to DC.
>All our cocos convert the incoming AC power to DC, albeit a lower voltage.
>If a matching computer and monitor are used on a power frequency(50 or
>60HZ), how can they have problems with sync, when there is no reference to
>the AC power frequency coming in?
I'm not Gene, and I certainly don't play him on TV, but I think I know the
Short answer: It doesn't matter -- sync and line freq are not locked
Longer answer -- it does matter, in that every country sets its vertical TV
sync rate equal (more or less ;-) to its power line freq, to minimize flutter
and flickering that would result at a 10-Hz "beat rate" between the sync and
power, IF the power supply capacitors were not doing 100% job of filtering
the AC power line ripple or "hum" out of your TV or monitor's DC.
You may remember seeing, on an old, well-wron TV, a horizontal gray smudge
bar that slowly crawled up or down the picture. That was the result of
failing capacitors in the DC supply. The bar barely moved because the vertical
sync rate sort of equalled the AC line frequency.
If there had been a big difference between the two, that bar would have kept
racing across the screen, making a flicker, and been even more annoying.
So -- the Fuji computer may well be set for a 50 Hz vertical frame rate, and
the US monitors you've tried can't tune down to it. I think some models can.
You could extend the vertical rate of a monitor down to 50 Hz with one
little capacitor change, but the vertical output circuit might draw excessive
current and overheat. So I'd look for a way to set the computer to 60 Hz, though
I'm sure you've looked already.
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