I have two IBM Power 7 machines - Power720 and Power740 (8202-E4B and 8205-E6B) and both have an internal USB 6 pin header (labelled J3_TAPEUSB_SIGNAL). These are for connection to a single device (either an LTO drive, an RDX drive, etc.).
The IBM cable is either unobtainable or the price is insane, so I decided to just make one myself.
I am going to mount an RDX drive (dock). I already got the parts (the RDX, a USB Type B cable and a Dupont style 2x3 connector). Now the problem is, how do I determine the header pinout (using a multimeter, etc.) without frying the motherboard, port or any device attached to it?
I searched all over the place for IBM-related pinout information to no avail. So this is basically a hands-on job, hopefully without toasting anything.
Any help or pointers appreciated.
EDIT:
These are resistance and voltage readings I took as per @KH's recommendations:
As for other components/devices nearby, this is it (bottom right SAS backplane cable removed for clarity):
I tested impedance on the front and back USB Type A ports (receptacles) and got 1.2 Ohms on pin 4 (which can maybe match pin 3 top right on the header). All others infinity.
All readings done against the chassis.