Yongnuo RF-603 Problem?

I have a set of these transceivers and they work as advertised when a flash is connected via hot shoe of the trigger. They will not, however, fire the flash via the PC connection with a PC cable. I have three different flashes (all in the approximately 6V trigger voltage range) and none of them will fire with the PC cable. Anyone have any thoughts on this?
Thanks,

Probably a loose connection, one of my units had this problem, just looking into the unit i was able to see one of the three conections was too recessed to properly function, opened it up and just put it back in its place with some added hotglue so it'll stay.

Thanks for replying. Loose connection is unlikely though. I have four of these transceivers and none of them work with the PC cable (which I know to be a good cable).

If you short the center pin and the outer ring of the PC connector that connects to the Rf-603 does the flash fire? A car key works great for this. If not the cable is bad. Try crimping the outer ring of the PC connectors slightly so they make a better connection. Not too much or they disfigure and will be ruined. These connectors are the worst connector ever invented for being reliable.

Well, color my face red! I have two of these sync cords and I've been using one on other equipment successfully. Turns out that I picked up the second cord to test these Yongnuos and, thinking that I had a working cord on the other system, it must be something else. Well, as luck would have it, the second cord actually is bad. Using the other cord (the one that worked fine on my other system) has the Yongnuos working as they should.

The bad cord has been sent to the place where all "bad" cords go!

Thanks, dedsen, for planting the seed.

Great. Glad to hear you got it working. It is always iffy when a PC sync cord is involved.