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
I had monitor with a problem where it would not power on correctly after it was off. It would just flash over and over again until it got warm, and then would start working and be fine until it was turned off for some time, and then back on again. These types of problems usually end up being something wonky with the power supply and often end up being caused by a capacitor or two that have gone bad. If you crack it open you can usually find them and simply replace them to get the monitor working again. This has happened to me a few times over the years and it's a relatively easy fix, so I thought I'd go over the process here with this one.
After cracking the case open and digging out the power supply, you can identify the bad capacitors by the bulgy bent up ones. Sometimes they will have some gunk on the top. In this case you can see the two caps here that are bad (the tall brown ones):
Using a solder pump, or wick, suck off the solder from the joints (note, I de-soldered the wrong lead in the bottom right, had to go back and de-solder the proper lead after noticing the cap wasn't budging)
And finally install new caps to replace the ones you removed. Make sure you use a similar spec cap. The ones I removed were 1000uF 16V caps, and I replaced them with 1000uF 25V caps. The same or higher voltage will be fine. Also polarity matters, so make sure you line up the negative lead on the cap with what is marked on the board, or the same orentation as the caps you took out.
Put it all back together and if everything went alright it should be working like new.
posted at: 18:56 | path: /electronics | permanent link to this entry
