Some of the new-revision IBM CGA cards have this yellow bodge wire. Classic IBM, right? But what is it for?

#retrocomputing

#retrocomputing The top chip is an 74LS244, an octal buffer. The pin the bodge is connected to, pin #5, is the output for the input pin #15. This pin is the light pen strobe.

The chip at the bottom is an 74LS245, an octal bus transceiver. Its job is to drive the CGA's data bus at specific times - when the CGA status register is read.

#retrocomputing The bodge connects to D1. This represents Bit 1 of the CGA status register. Which is, accordingly, the light pen strobe.

When IBM redesigned the CGA card to make the "new" model, they forgot to run a trace. This means that the light pen won't work on any new model CGA card without this bodge.

#retrocomputing Given that the light pen on the IBM PC was pretty much dead on arrival, this was probably not a problem for the average PC user.

Which makes me wonder - did IBM start applying the bodge at the factory, or did they just add it if someone complained?

@gloriouscow This is just me, but somehow I have a feeling they probably did this at the factory. Just seems like their way to me.

RE: https://oldbytes.space/@gloriouscow/115680609373266137

@nazokiyoubinbou @gloriouscow

I agree it could have been done at the factory. A jumper like that could be the difference between printing a one sided board or needing two sides.

Not all jumpers are "bodges"

@futurebird @nazokiyoubinbou The evidence for it being a bodge is that it is not present on all new-style CGA cards.

The card is already four layers with signal traces on both sides.