IBM AT Drive Types

Tony Duell ard at
Tue Jul 12 13:45:03 CDT 2005

> Its my understanding (but I've only seen it as a rumor, not as hard
> technical fact) that the reason the original IBM Monitors plug into the
> PC Power Supply and not directly into an outlet is that they were
> vulnerable to damage (probably the same horizontal drive problem) if
> left powered on independent of the PC.

I've heard that rumour too, but I can't understand why, after looking at 
the schematics. The horizontal drive is transformer-coupled, so it 
doesn't matter if the input gets stuck high or low, it still won't turn 
on the output transsitor. 

> I at one point had an original IBM monitor that had a direct power cord
> connector and understood at the time that it was one of the very early

The CGA and EGA nonitors of course connect separately to the mains. The 
MDA monitor has a built-in power cable ending in an IEC plug that would, 
in theroy, fit into a normal 'kettle lead'. AFAIK all were built like that.

I am using a 5151 now. On the grounds it doesn't have a power switch of 
its own, I plug it into the outlet on the system unit PSU. I suspect, 
though, it would do no damage to power it separately.


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