A couple of days ago the lights on my fishtank came on in the morning, but when they did they were flashing on and off like some kind of underwater disco show. I don't think my fish appreciated it much, and so I disconnected the light and started looking into the problem. The lights on the tank are a track of LED lighting that are powered from a 15.2V 1600mA power brick. I figured that was where the problem was and sure enough putting my mutlimeter on it I noticed it fluctuating around a bit. I decided to put my scope on it to see what was going on and got this:
Here we can see the supply is jumping up to 12.5 volts, then dropping down 2 volts every 200 miliseconds or so, which explains why the lights were flashing on and off, but this certainly isn't the desired output. Next up was to open it up and see if anything looked wrong. This proved harder than expected since there wasn't a single screw in the brick design and it was just glued together. I ended up breaking the seal with a screwdriver and finally pried it apart. After some poking about I noticed this one capacitor looks like it had shot its load onto the heatsink.
And here is a not that great picture of the bad cap after it was out, you can see the brown electrolyte that leaked out of the cap
And after replacing it we get a steady 15.2V from the supply as it was designed to do (it's not exactly a clean supply, but it does the job for lighting leds)
Ended up epoxying the plastic case back together and almost as good as new :)
posted at: 00:47 | path: /electronics | permanent link to this entry
