On 7/15/2014 5:59 PM, Leonardo Marsaglia wrote: > There are some big electrolytic caps inside the cabinet (80 mm diameter and > 180 mm long approx). I can replace them easy but is there a way to know if > they are faulty before replace them?
Physical examination is the first step in diagnosing electrolytic capacitors for faults. Check that the tops of the capacitors are not bulged or split open. If they're not flat, they're bad. If they're split open with goo coming out, yup, bad. Also look for evidence of leakage under the capacitors onto the circuit board. That can be quite nasty as the electrolyte can corrode through traces on the board. Capacitors can leak from their bottoms without bulging or splitting the tops. Bottom leakage can be hard to detect. Look for dust that won't blow off or areas that are darker than the rest of the board surface. Bad cases can look like dried cat pee on the board, and just as corrosive. I once had a cat that decided the CRT on a Xerox 820-II was "his" and needed "watered". The pee ran down the face of the CRT then dripped onto the main circuit board, eventually damaging it. > My brother has a digital oscilloscope that can measure capacitance but I > don't know if that's ok for this kind of capacitors. But I guess if they > are in the range the oscilloscope can measure I might work. Testing the caps out of circuit is more accurate, but then you've already taken them out so why not just replace them anyway, unless they're a hard to find style or you're really pinched for funds. In circuit testing can at least identify caps that are definitely bad electrically even though not visually obviously bulged or leaking. Cleaning the board is simple. A toothbrush, hot, soapy water, a rinse with clean (preferably distilled) water then a long stay in the sun to dry or use a convection oven or food dehydrator at 100F or lower for a couple of hours. Could be cleaning is all that's needed. It can temporarily clear up problems from minor base leakage by removing the electrolyte that's causing improper capacitance or conduction among traces and pins. The capacitors will still be leaking and their values will be off. What's extra bad is when enough electrolyte leaks out that the rolled up metal plates short together. Then you get things like explosions and physical and electrical damage to other components. Once the "magic smoke" is let out of electronics it tends to be expensive to put back inside. ;) Your lathe may be yet another victim of the "capacitor plague", which is still claiming electronic victims. This plague involves some industrial espionage, a stolen electrolyte formula and unknown millions of counterfeit electrolytic capacitors made to look like well known brands, but just a bit cheaper on the wholesale market than the genuine ones. The stolen formula was unstable and capacitors made using it will nearly always fail, eventually, sometime. It depends a lot on how and how much they are used, or not used. Some failed in a very short time. Some lasted 20+ years just fine, only to burst open in storage. Apple Computer ended up with tons of bad caps that were put into Macintosh computers built in the 1990's, thus there's a cottage industry in recapping old Mac circuit boards when people dig their old computer out of the closet and find it no longer works. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ------------------------------------------------------------------------------ Want fast and easy access to all the code in your enterprise? Index and search up to 200,000 lines of code with a free copy of Black Duck Code Sight - the same software that powers the world's largest code search on Ohloh, the Black Duck Open Hub! Try it now. http://p.sf.net/sfu/bds _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
