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From: tj@gpu.utcs.toronto.edu (Terry Jones)
Date: Wed, 20-Jan-88 15:37:30 EST
Message-ID: <1988Jan20.153730.8333@gpu.utcs.toronto.edu>
Organization: University of Toronto Computing Services
Newsgroups: comp.sys.ibm.pc
Subject: Re: Screen blanker for Hercules GC
References: <1976@ncr-sd.SanDiego.NCR.COM> <129@mccc.UUCP> <1297@vu-vlsi.UUCP> <25@infopro.UUCP> <4436@ecsvax.UUCP>
Reply-To: tj@gpu.utcs.UUCP (Terry Jones)
Distribution: na

In article <4436@ecsvax.UUCP> dmkdmk@ecsvax.UUCP (David M. Kurtiak) writes:
>such a mishap as the result of any software.  In other words,
>how does this screen blanking program go out and sizzle the
>components?  I can see if I applied a kludge to the card by ways

The card itself usually isn't harmed. Usually it is the monitor.
On a composite monitor the thing scans on its own, then if you
cive it a signal it locks onto that and scans at the signals frequency.

On a TTL monochrome monitor you get the scanning from the signals from the
PC and the monitor usually doesn't scan on its own. The currents that
flow through the monitor circuitry are quite different in a "dynamic"
state (when scanning) then they are when the monitor stops scanning. Often
transistors are on steady instead of for 10 or 20% of the time like they
are when the monitor is scanning. The overheat when on too long. (in an
on or conducting state). IBM made the mono monitor plug into the PC
for a real good reason. When the PC is off there are no scan signals
for the monitor so they want the monitor off. There are three ways to
fratz a ttl mono monitor. 1) unplug the video cable to it while on. 2) plug it
in somewhere else and forget to turn it off when you turn off the PC 3)
via software turn off the video signals. 

Now there are going to be a trillion of you out there that say well I have
a frimfram monitor and I leave it on for weeks and it doesn't do what
you say... or I have use this screen blanker and it works fine with my 
setup. Sure. Some monitors can take it. The IBM TTL mono can't. This is
has been statistically shown. Your mileage may vary as they say. Do it
any way YOU want.