When I renovated my house I decided to install Clipsal C-Bus dimmer packs as part of my home automation system. All was good but over time I started to experience a worrying fault. After a lamp blowing the channel it was connected to would become permanently on, this Instructable will take you through the trouble shooting process and hopefully the repair. If your dimmers are still under warranty I would try returning them first. Whilst I have focused on the Clipsal C-Bus dimmers this could apply to any triac dimmer ti one degree or another.
CAUTION: This project involves Mains Voltages. If you don't feel satisfied you can work on this safely or you do not hold the qualifications required in your location please do not proceed.
Step 1: Whats Wrong?
At first I thought the issue might be with the config so I reloaded the configuration using the C-Bus Toolkit. The issue remained and I was still unable to turn off the channels with the problem. My gut feeling was that this may be an issue with the triacs so the next stage was to remove the dimmer pack from the installation.
Step 2: Removing the Dimmer Pack
Every installation will be different but in my case the removal was as follows. The fist step is to remove the dimmer pack from the enclosure. Before starting this I isolated the power supply (luckily my installation has a separate breaker per dimmer pack which meant I could leave the rest of the system operable) to the dimmer pack in question. If however you are not confident working around live electrical circuit I would recommend you isolate the entire panel.
With the power isolated it was just a simple matter of removing each of the mains wires one by one. Mine were already labelled, if yours aren't I would suggest you do so to make sure things go back in the same place! Finally you will need to remove the rj45 data plug from the unit.
Step 3: Getting Inside the Dimmer Pack.
Getting inside the dimmer pack if by far the most difficult part of the repair as the pack is glued together. You will need to carefully cut through the glue on the corner of each of the purple covers. Whilst the picture is some what of an exaggeration I did find that carefully driving a blade between the glued surfaces was quite an effective method.
Once you have purple covers off in least in my case there is just a small spot of glue on the back and then everything just unclips.
Step 4: Finding the Problem
Once I had extracted the board with the triac's and inductors and removed the heat sinks I did a quick visual inspection. Sadly there was nothing obvious but I still had a gut feeling it was down to a failed triac's. Using a multimeter I measured the resistance between the live power input and each of the channel outputs in turn. The two failed channels were a dead short. I then did the same between the T1 and T2 pins on the individual triacs and confirmed they were a dead short.
Step 5: Replacing the Triacs
First step is to de solder the failed triacs, I used a simple solder sucker and soldering iron, although de soldering wick is also an option. Once I had them out I did a quick test of them once again to confirm they were the cause of the issue, I also check the channel with the triac removed and confirmed it was no longer a dead short.
As I was happy I had tracked down the cause of the issue I soldered in replacement triacs I had purchased "just in case" they were the cause of the problem taking care to make sure they were orientated correctly. The ones I had purchases with a slightly different package but not enough to cause any issues.
Once they were soldered in I did a quick continuity test between the terminals and the triacs.
Step 6: Putting It Back Together.
Putting it back together is pretty simple, just the reverse of the dis-assembly. Until it was tested I just assembled it without glue, once I was happy it worked I popped the purple front covers off and glued the back in place.
Step 7: The Moment of Truth
With everything reassembled and installed back in the enclosure it was time for the moment of truth. I turned the power on and everything worked! This was quite a cheap fix with the triacs costing about £2 each, other than the solder and a dab of glue they were the only expense. Getting in to the case was however a nightmare but if you take your time you will get there in the end.