[Coco] CoCo3 RGB w/Samsung Syncmaster 150MP/170MP

[John B]

Understood.  I have the RGB2VGA board w/DE0 Nano.  It works fairly well.  I
wanted to see what a native signal would look like.  The Cocopedia page
said the Samsung Syncmaster 150/151/170/171 MP could do 15KHz natively.
They are readily available and cheap so I figured I would try it.  No
luck.  Someone will need to update the page and omit those monitors.

On Sun, Aug 16, 2015 at 2:05 PM, Gene Heskett <gheskett at wdtv.com> wrote:

> On Sunday 16 August 2015 13:33:53 John B wrote:
>
> > On the CoCopedia page under "15KHz monitors" it lists the Samsung
> > Syncmaster 150/151/170/171 MP.  Has anyone actually used one of these
> > monitors with the CoCo3 using RGB?  I have a 150MP and 170MP and
> > neither will display a picture.  The monitor doesn't even recognize
> > the signal.  I have triple checked the wiring etc.  The documentation
> > for the monitor states the horizontal frquency starts at 30 KHz.  Is
> > there some special undocumented mode or modification that needs to be
> > done to the monitor?
> >
> > Thanks
> >
> > John
>
> The monitor is protecting itself.  Its a 31khz minimum frequency design,
> and taking the magnetic bits down to 15 khz would handily saturate the
> ferrite cores in the transformers.  That cannot be allowed to occur,
> ever, as a saturated ferrite core simply disappears from the circuit,
> leaving only the coils air inductance to limit the rate of the current
> rise. It will rise to destructive levels in just a couple microseconds,
> probably shorting the scan power transistor, and that will casade back
> thru the power supply, destroying semi's in the power supply until such
> time as a 10 cent fuse can manage to clear, usually before the service
> breaker feeding that wall outlet can clear.
>
> The repair bill in that event is often substantial enough to start
> hitting yard sales for another monitor.
>
> It should however, work great (properly wired cabling assumed) on most
> any of the VGA translators from Roy J.'s to what Ed is making now.
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
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> -Ed Howdershelt (Author)
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>
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