Xref: utzoo comp.sys.ibm.pc:15996 comp.arch:5019 comp.graphics:2588
Path: utzoo!attcan!uunet!cadnetix.COM!cadnetix!jiml
From: jiml@cadnetix.COM (Jim Lewczyk)
Newsgroups: comp.sys.ibm.pc,comp.arch,comp.graphics
Subject: Re: How did this program burn out two monitors?
Message-ID: <2739@cadnetix.COM>
Date: 26 May 88 20:12:05 GMT
References: <10244@agate.BERKELEY.EDU>
Sender: news@cadnetix.COM
Reply-To: jiml@cadnetix.COM (Jim Lewczyk)
Organization: Cadnetix Corp.,  Boulder, CO
Lines: 30

In message <10244@agate.BERKELEY.EDU>, willis@violet.berkeley.edu
(Willis Johnson) reports:

>The second 
>monitor burned out too!  I thought it was impossible to damage my
>monitor and adapter with software.  Does anybody have any ideas 
>what caused this? 

I have heard from my cronies of the existance of the rare 
HCF (Halt -- Catch Fire) instruction in some IBM PCs.  The 
condition, if I remember correctly, was caused by the horizontal 
sync pulses (or was it the vertical?) not being generated either 
because the video adaptor was halted or was never initialized 
(the Halt part).  

Normally, this would not be a problem because the monitors have 
internal oscillators which simply run unsynchronized, but in 
this case the sync pulse to the monitor was stopped in mid pulse,
ie, ON, and the internal oscillator was simply stopped.  The 
drive transistors for the horizontal oscillator are heat sinked, but
even so, they are not designed for DC operation, so they burn out (the 
Catch Fire part).

I would not think this was possible if the monitor makers took the 
minor precaution of AC coupling their sync inputs, but it would appear 
that even this protection went the way of the cost cutters.
 James Lewczyk,  Cadnetix Corp.          Internet: jlew@cadnetix.com
 5775 Flatiron Pkwy, Boulder, CO 80301   UUCP: cadnetix!jlew
                                         {uunet,boulder,nbires}!cadnetix!jlew
"Give me one good reason why I should be rational!"