Xref: utzoo comp.sys.ibm.pc:15829 comp.arch:4955 comp.graphics:2535
Path: utzoo!attcan!uunet!husc6!think!ames!pasteur!ucbvax!decwrl!labrea!glacier!jbn
From: jbn@glacier.STANFORD.EDU (John B. Nagle)
Newsgroups: comp.sys.ibm.pc,comp.arch,comp.graphics
Subject: Re: How did this program burn out two monitors?
Message-ID: <17460@glacier.STANFORD.EDU>
Date: 24 May 88 05:29:15 GMT
References: <10244@agate.BERKELEY.EDU>
Reply-To: jbn@glacier.UUCP (John B. Nagle)
Organization: Stanford University
Lines: 14


       This is an old known bug.  You can burn out the IBM monochrome
monitor by stopping the horizontal sweep while keeping everything else
running, and the Hercules card gives you enough control to do this
under software control.  The video chip lets you select the horizontal
and vertical sweep rates independently, and zero rates are possible.
However, the horizontal sweep is used as the oscillator for a switching
power supply, as is typical in TV circuits, and with the sweep rate at
0, DC flows through a coil with high inductance but low resistance,
producing an excessive current that burns out the coil.

       Part of the problem is that the IBM monochrome monitor is a design
lifted from an earlier, pre-PC product line, the IBM Displaywriter, and in
that product, there was no potential vulnerability of this type.