27 Mar
2010
27 Mar
'10
4:10 p.m.
If it's the original IBM5151 monitor, remember there's no horizontal
oscillator in the monitor. The Hsync (or more correctly HDrv, which is
what IBM called it) output from the MDA card goes to the base of the
horiztoal driver transistor, the collector is then transformer-coupled to
the base of the horizotnal output transistor.
This means a 5151 will try to run at whatever freqeucny you give it, the
horizotnal output stage is likley to protest if it's way off, though. I
don;t think that if you give it an HDrv of the wrong frequency it will
ever give you a double image.
-tony
It is a 5151. I was able to reproduce the problem on a newer monochrome
monitor.
bd