View Full Version : Anybody every seen this? (IBM PC/XT content)

April 24th, 2016, 10:10 AM
Hi guys,

Following the weird floppy drive issue of an old IBM 5160 I got, I was cleaning it up and took the mainboard out to find this:


It's in the CoPro socket, but I have no idea what it's for... anyone seen this before and know what it does? Switch 2 is still set to ON (no CoPro installed), so it looks kinda redundant to me anyway :oops:

April 24th, 2016, 10:15 AM
Looks like a timing tweak with some small-value polystyrene caps. What pins are connected?

April 24th, 2016, 10:41 AM
It looks like somebody's jury rig attempt at an 8087 emulator. :-)

April 24th, 2016, 11:00 AM
If the other end of those caps goes to pin 29 or 30, then I'd check the bottom of the PCB for a jumper wire--these are supposed to be NC on the 8087.