Advice about repairing an IBM 5151

Fred Cisin cisin at
Sat Aug 29 20:29:06 CDT 2015

>> I am trying to identify why my IBM 5151 display has no picture when
>> connected to a normal MDA card in a IBM PC 5150. So armed with an

On Sat, 29 Aug 2015, william degnan wrote:
> There is a 2nd connector for the video card of the 5151.
5151 is a monitor number.
> I can't quite tell
> if you mean you have the video card that comes with the 5155 and you're
> trying to test with a card that came from somewhere else or something else.
> I am unsure if the 2nd connector pertains to the internal or external port,
> but you want to be sure you have this in place.

He said 5151 connected to MDA in 5150.  That would have little or no 
overlap with what the 5155 has.

The 5155 does not use an MDA, although one COULD be added for a second 
monitor.  The 5155 uses CGA.  The CGA has three video outs.  There is a 
DE9 RGB video out, for color monitors.  Should never be connected to a 
5151 or other MDA/MONO(MDA)/Hercules monitor!

The CGA also has an RCA with composite (almost RS-170) video out.

And, the CGA has, just inside the bracket, a 4 pin sometimes keyed Berg 
connector that was originally intended for an RF modulator such as the 
SUP'R'MODII.  That connector has voltage and composite, and is used in the 
5155 for the internal monitor.

The CGA also has a 6 pin Berg connector for light-pen.

He said 5151 connected to MDA in 5150.  So, none of the CGA stuff applies.

The MDA board, has a DE9 for IBM MDA MONO (sometimes called "Hercules" in 
a futile attempt to avoid ambiguity).
The IBM MDA board also has a DB25 parallel printer port (sometimes 
erroneously called "Centronics").  Hence, the IBM board is called MDP, and 
there are many AFTER-market MDA boards.
Some of the IBM MDA boards have a light-pen connector?

More information about the cctech mailing list