Xref: utzoo comp.sys.ibm.pc:15874 comp.arch:4968 comp.graphics:2545
Path: utzoo!attcan!uunet!husc6!bloom-beacon!tut.cis.ohio-state.edu!mandrill!neoucom!wtm
From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: comp.sys.ibm.pc,comp.arch,comp.graphics
Subject: Re: How did this program burn out two monitors?
Summary: 6845 Chip on CGA, MDA, and Herc boards
Message-ID: <1195@neoucom.UUCP>
Date: 24 May 88 13:28:03 GMT
References: <10244@agate.BERKELEY.EDU>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 19


If you tinker with the registers in the 6845 CRT controller chip on
the video board, you can program in a horizontal scan rate that
will overheat the power supply in the monitor.  The reason being
that a monochrome monitor is designed to only work within a very
narrow range of horizontal frequencies.  The problem seems to come
from accidentally programming a 6845 on a herc display with values
that are appropriate for a CGA monitor.  Such a mistake is pretty
easy to make whilst tinkering with graphics programming and
accidentally using the wrong setup from a library.  Doing herc
graphics with Borland's BGI system seems to be pretty safe, as I
still have my herc monitor intact.

Several people reported that a screen-saver program called
"BURNOUT" fried hercules _boards_, rather than the monitor.  This
surpirses me, but several people were quite emphatic that it was
the board that went south.

--Bill