I have a TR-505, Sound Canvas Sc-55, 2 keyboards and a PC conected through a MIDI patch bay (This means that I can route any equipment to any other).

It's possible to tap the TR-505 and listen the sounds on the module or PC , or play the pre-programed patterns and listen on them.

It's also possible to play the keyboard and listen the sounds on the TR-505.

Confirm that your pre-programed patterns are running (look if the led flashes or if the TR-505 makes sounds). Is your MIDI sync adjusted to Internal or External?)
You have to press shft MIDI button several times to pass through all the MIDI functions.

The only point you have to pay attention is if your MIDI sync and MIDI channel are compatible (between PC and TR-505).