Control/Dimming Leviton D4DMX Box Channel Stuck at Full

[RealPerson]

I have a Leviton D4DMX dimmer box that has a channel stuck at full. The other 3 channels respond perfectly to DMX control but Channel 4 on the box is constantly on. Even when the box itself is turned off with its power switch channel 4 stays at full. The only thing that works to turn it off is to unplug the box. I opened it up and took a look at the inside as I have worked on intelligent fixture repair before but didn't initially see anything that stood out as wrong. Has anyone else ever experienced this or have advice on how to fix it?

 

[RickR]

Someone let the magic smoke out. SCRs are hard too diagnose visually.

 

[derekleffew]

A thyristor (triac) will fail either open or closed. There will likely be no visible damage. They're ridiculously inexpensive and usually not difficult to change if one has soldering experience. I believe someone on here advocates using a 40A rather than a 15A for a few pennies more.

Leviton was purchased by NSI in the 1990s so the Leviton D4DMX and NSI D4DMX are the same product, and very similar to some from Chauvet and ADJ, as well as generic China