[Coco] Step down transformer for use in UK / Use on TV in UK

[Joel Ewy]

Joel Ewy wrote:
> ...
>> Also, this question may have been visited before, and probably asked by me 
>> anyway. I note the Coco 3 has the RF output and the audio/video sockets. 
>> Will it work, using the standard cables, on a PAL TV. However, my TV is 
>> NTSC compatible.
>>
>>   
>>     
> If your TV is really NTSC compatible, then I suspect you should have no
> problem.  Does the TV have different antenna connectors for NTSC vs.
> PAL?  Does it have a manual switch?  Or does the TV automatically sense
> the type of signal it's getting?
> One thing that may be an issue:  The CoCo's clock works by counting the
> AC power zero crossings.  In the US the power lines use 60Hz, while for
> you it would be 50Hz, I think.  There are 50Hz clock driver modules for
> (Nitr)OS-9, etc.  This clock may be unrelated to the video signal,
> though the vertical sync signal of an NTSC signal is 60Hz, and I think
> that of PAL is 50Hz.  Software that uses the mains-based timer to sync
> up with the video signal might get confused?  Your machine might be
> something of an oddball if it's an NTSC model, but using a 50Hz clock. 
> Others may be able to tell you what the full ramifications of this might be.
>
>   
I realized after I wrote this that it doesn't make sense.  As Phill
points out, and I know from experience, you can run an CoCo 3 from a DC
power supply.  If the CoCo's clock interrupt comes from the AC power
supply, then how can this work?  I'm sure I didn't just make up the
stuff about the zero-crossing circuit (isn't this one function of the
SALT chip?), so what am I missing?  I see several possibilities:

1.  I really am making the whole thing up.
2.  It's only the CoCo 1/2 that get their clock interrupt from the
electric company, while it's derived from the crystal on the CoCo 3.
3.  There's still enough ripple in a rectified, regulated DC supply to
trip the zero-crossing circuit and generate interrupts.

Someone will surely step in here and provide a better answer.

JCE
> Good luck!
>
> JCE
>   
>> Best wishes
>> Steve 
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