[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.
--Mike K.

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