Convert from VGA 9 pin to RCA (manually - old machine)
There are a number of problems you have here:

VGA is 15 pins, not 9

RCA is composite video, not VGA

IBM 5151 is neither of those, it's an old standard &quot;MDA&quot; (monochrome display adapter).


It appears from the internet that MDA isn't a subset of VGA - you can't convert from one to the other by simple wiring.
Your options are:

find an old IBM 5151 that is still working, or repair the broken one

buy an MDA to VGA converter and wire it appropriately. &quot;Industrial&quot; versions of these can be found on Aliexpress and other vendors; it seems that this is a common problem of industrial equipment with obsolete monitors.

trace the video signals further back from that board and find a more useful one (unlikely, since this looks very old .. how old is it? 80s?)