I'd suggest always test ripple at 3 states: no load (0A), light load (1-10mA), heavy load (50-80% of rated wattage). Seeing if the results vary (and by how much) tends to sort the wheat from the chaff in their quality. ~7mV ripple RMS at no load isn't astoundingly quiet, but decent, maybe good for SMPS. If keeps that figure up into high load you can guess it was likely designed very well for its spec, though.
Excellent new channel! I wish you all the best success and look forward to new videos! Good pace, clean editing, good video and audio.... SOMEONE watches Mr Carlson's Lab! I wonder if a thermal camera would have helped diagnose this?
Thanks for the kind words about the channel and videos. The defective optocoupler didn't overheat (no noticeable temp difference from other optocoupler when touching it) so I don't think a thermal camera would have pinpointed the problem. It was really that the part was very sensitive to external temperature changes.
Great repair! Did you check the solder joints on the opto prior to replacing it (maybe I missed something)? Always fascinating, how much noise even quality SMPS generate compared with a good old linear supply. Also, this supply is very difficult to measure "correctly" with the binding post so far apart. The large loop might have introduced some additional noise to the measurement as well. Although I almost always enjoy TME repairs more than other content, it would be interesting to hear whether you do other work as well, like circuit design (hobby or professional). So if there is ever a shortage of things to repair, from time to time projects might be interesting as well. Keep up the good work!
Thanks, yes I did inspect the solder joints before I removed the part and they looked ok. Yes SMPS have trade offs for the high efficiency, and suppressing the electrical noise is not easy. The noise measurement was made without any other wiring (other than o'scope probe) connected. I will try to cover plenty of topics in electronics. Thanks for watching!
Yep, an optocoupler failure on a SMPS is not too surprising. Depending on your intentions for the unit, - keep it for use, or sell it to make a profit - I would replace the big smoothing cap in the middle of the circuit, as general maintenance. I would also look for any type of a memory battery. But, you know these things... Just thinking out loud. Thanks for the caution on a floating/powered heat sink. I must really keep it in mind that a SMPS is like a very mean dog. Reach out to pet it and you might get bit, hard.
No memory battery in this power supply. I'm keeping the power supply for personal use (and it's not the main supply on the bench) so I did not get into the capacitors at this time. They are working ok but if one fails in the future I'll deal with it at that time. Yes watch out for high voltages in these SMPS, don't get bit!
I’m currently looking at a kepco power supply that sits at max voltage as well but it doesn’t seem to return to normal after heating up, and only spikes as soon I attach a wire. Do you think it could be a similar problem?
Nice video but for those of us who do not live in USA it might be useful to qualify that your temperature settings are in degrees 'Fahrenheit'. Just saying!!😁
Thanks, and I actually realized what you said about the temperature after I uploaded the video. I will be careful about clarifying F/C ratings on future videos.
