I retired in 2016 after 34 years as the metrology supervisor at a commercial nuclear power plant. I couldn’t count the number of equipment failures due to electrolytic capacitors, WAY TOO MANY. Some brands of equipment had high percentage failures while other brands had low. Seems the manufacture of the CAPACITOR was a better indicator of failure rate. Many equipment manufacturers used capacitors that carried brands from Japan, others used Sprague (which is probably made in Japan as well, but seemed to hold up much better). Leakage current and capacitance value change seemed to be the culprits most of the time.
For our “standards” we added a step to our calibration procedures to check all power supply ripple voltages to insure they were in spec. For all other test equipment, we would do the ripple checks any time the equipment was in the lab for repair. Also, the plant itself had preventative maintenance procedures to energize certain (safety critical) electrolytic capacitors in our warehouse once a year. Sent from my iPhone > On Apr 15, 2020, at 3:33 PM, Ray Albers <rayalb...@gmail.com> wrote: > > I could use some knowledge and/or opinions on this subject (Radio/Elecraft > related only because it deals with a power supply that powers a K3!) > > The other day I was about to initiate a call, and as soon as I touched the > "dah" paddle the K3 instantly shut off. The cause was that the power > supply voltage dropped too low when the radio demanded more current. > > The power supply is an Astron RS-20A, a big hulking linear supply that I > really like. Huge heavy transformer and two series-pass transistors mounted > on big heat sinks - thus, quiet acoustically (no cooling fan) and > electrically (no RF hash from switching). I have two of these - one that I > bought for my new radio when I got back into ham radio after a long > absence and the other because I was at a hamfest where someone had a pile > of them that he was selling for only $20 each - who could resist? So I > trotted out the spare supply and got back on the air. Now to troubleshoot > the bad supply. > > I had trouble with this one about five years ago. The output transistors > are plugged into sockets, and on one socket the contacts for the emitter > pin had gotten loose, and there was a vicious spiral of heat causing more > resistance causing more heat until eventually it actually melted the > transistor pin and left a black char on the socket. When I replaced the > socket that time, I decided to solder the emitter pins on both transistors. > > It took me a long time to find the problem this time. Various tests told me > the transformer, the full-wave rectifier diodes and the pass transistors > were fine. Finally - with some help from hints in a great article about > Astron supplies on repeaterbuilder dot com - I figured out that the supply > voltage to the regulator board was too low, so there was not enough "oomph" > available to drive the output transistors when high current was demanded. > > This supply voltage comes from a center tapped transformer secondary > feeding two small diodes (both of which checked OK) to a 1000uF 35 V > electrolytic. Turns out the capacitor was bad. It's a typical aluminum case > with blue plastic covering (which I assume to be heat-shrink plastic > because of the way it is completely molded around the capacitor.) > Replacing it brought the supply voltage up to spec, and now everything > works fine. > > But I was surprised about the capacitor failure. Absolutely no visible > signs of anything wrong - no bulging, leaking, etc. And the soldering to > the PC board is perfect. So here's my question for the group: What do we > know about electrolytic capacitor failures? I know that anyone restoring > an old ham transmitter or receiver or BC receiver almost always has to > re-cap it, because the ancient electrolytics, which are usually wet > electrolytics in chassis-mounted cans, will have gone bad. But this is the > first time I've ever had a failure of the more modern type electrolytics. A > quick search of capacitor failure on Google shocked me when I read claims > in several places that these capacitors are only expected to have a two to > five year life!! Can that be? I know I've got lots of radio gear that's > way older than that and still working fine. To do this repair, I replaced a > capacitor that might only be 5 years old with one that is probably twenty > years old! > > Words of wisdom and enlightenment would be most welcome! > > 73 > Ray K2HYD > (K3 #8240, KX-3 #6827) > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to hsherr...@reagan.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
