There is probably (a 90% chance) a problem with MOC3051 device used as a optical isolation and driver of triac. Since 2013, we have received a number of service calls, when Farchild made semiconductor failure for unknown reason. The replacement of MOC3051 sorts out the problem. Most of the SRS Group dimmers have already precise sockets installed inside so the replacement is easy. However, on some models you still need to de-solder the DIP8 and replace it by a new one. Due to the RM in between of device's legs, you're unable to use a precise socket.
In case of this problem, please contact us for the spare part.
SRS Group marks "0" as OFF position, that is usually located on the bottom side of the DIP switch.
To activate the switch, move the lever to the upper position according to the numbers located on the device rather than numbers on the DIP switch.
See the picture below as an example of correct DMX start address setting for #1.