[Coco]50/60HZ FM-77AV video sync problems

[George's Coco Address]

----- Original Message ----- 
From: <KnudsenMJ at aol.com>
To: <coco at maltedmedia.com>
Sent: Tuesday, April 11, 2006 9:57 PM
Subject: Re: [Coco] FM-77AV video sync problems


>
> 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
> answer.
> Short answer:  It doesn't matter -- sync and line freq are not locked
> together.
> 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.
>

 This is true on a "broken" set.
  If you are watching a TV channel that is on a different power grid(I can), 
then you will see the horizontal shadow lines scrolling up or down.
 I can also attest to the fact that the coco does not exactly match the 
power line frequency on the vertical synce. So why don't I get these shadow 
lines scrolling on my screen? And why do I not get a SYNC problem as a 
result?
 When I test my generator set(motor, generator, third emergency standby 
backup), and I KNOW it isn't exactly 60HZ, I don't have problems. Even when 
the AC kicks on and the generator slows down, going HUFF, HUFF, and then 
catches up, the coco doesn't miss a lick. This PC doesn't miss a lick. 
However, this cheap APEX TV does shrink the screen a bit. The regulator in 
that thing sucks canal water. It never loses SYNC and just keeps going on.
 My microwave oven does loses it's time(too little voltage during this 
surge), but the computers NEVER miss.

 Again, I was talking about a matching computer and monitor. I'm in Texas! 
We use 60 HZ and it doesn't matter where you are, I still don't see how the 
power line freqency can  affect a MATCHING COMPUTER/MONITOR system. I even 
think that if you play a VCR tape from a VCR to a compatible TV, it should 
work no matter what you power line freqency is. They ALL run on DC and are 
crystal controlled, and NEVER precisely on frequency.

 It just doesn't figure.

> 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.
>
>