11 Jul
2005
11 Jul
'05
11:14 p.m.
The scanning frequencies of the EGA and MDA cards should be real close
(MDA outputs 348 lines of res, the EGA 350). You shouldn't have a
problem there (I won't comment about the jumpering/shorting though), but
keep in mind the original IBM mono monitor was very very touchy. If you
plugged it into a CGA card, it was known to...ummm...explode...
That's going a bit far. It's very easy to burn out the horizontal output
transistor and maybe associated components, but it won't explode.
There is no horizontal osciallator in the MDA (5151) monitor. The Hsync
line goes to the base of the horizontal driver transistor, the collector
of which is transformer-coupled to the base of the horizontal output
transistor. You can therefore attempt to drive the horizontal system at
just about any frequency, but if the horizontal output stage is driven
way off resonance (e.g. using the CGA frequncies), it will do nasty things.
I won't swear to it, but I had thought there was a way of configuring
it specifically for a mono monitor. Don't hold me to it though.
There is. There are switch settings for the EGA card to drive the MDA
monitor, CGA monitor, or EGA monitor (the latter can operate at 2
different horizontal frequencies). The reason I mentioned the jumper link
is that a lot of people forget to set that correctly when linking to a
CGA or MDA monitor.
-tony