I am usually pretty good at troubleshooting but this one has me stumped. I loaded a show in yesterday and they are using four Studio Spot 575s, that is the only thing on that line of DMX. I was called in today to move a projector, I am the lift operator/rigger. While I was there the LD asked to go up and check two lights that weren't responding, they were both flashing a shutdown message. He asked me to check the connections on both lights, the last one working and the first not.
Now to the troubleshooting, I didn't like the way the jumper from two to three was so I reseated it and had the LD restrike three and four. They showed they had signal and the addresses were correct but the still wouldn't take commands. Also, once they homed the display would go blank. I jumped around three to see if four would work solo, nothing. We decided to pull four down and use the spare. In the process we discovered if four was unplugged from AC then three would work. We hung the spare and got the same result so we changed address to see there was a conflict, same thing. We changed power to another curcuit in the breakout, nothing so I ran a homerun of power, same thing. Then three started a lite error so we replaced it with the original four. So now the old four is in the three spot, the spare in four spot with the same symptoms. I also tried putting an isosplitter between two and three, same result. To get the three light working I had to unplug four from power but I had to have the DMX line attached. If I took the cable out between three and four, I lost control of three.
The only two things I didn't do was replace the cable between two and three or try a terminator. Neither the lighting company nor the rental house believe in them. I am constantly having issues with these two outfits. Three pin cable comes from the rental house and I have never been able to determine if the cable is made for DMX or just audio cable.