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

[Gene Heskett]

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
-- 
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