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Assembly Manual ESR & Low Ohms Meter by Bob Parker Reproduced in part by arrangement with Electronics Australia, from their January 1996 edition. Please read Disclaimer carefully as we can only guarantee parts and not the labour content you provide. Cat No. K 7204 K I T currents, the electrolyte will start to decompose and the dielectric may deteriorate - and the ESR will increase far more rapidly. To make things worse, as the ESR increases, so does the internal heating caused by ripple current. This can lead to ACN 000 908 716 If you repair switch-mode power supplies, TV receivers, computer monitors, vintage radios, or similar equipment, and/or if you need to measure very low values of resistance, this project can save you lots of time and aggravation - as it has for me. It measures an aspect of electrolytic capacitor performance which is very important, but normally very difficult to check: the equivalent series resistance, or `ESR'. ome wise person once said, "The reliability of any piece of electronic equipment is inversely proportional to the number of electrolytic capacitors in it", and I doubt that many service technicians would disagree! Especially now that switch-mode power supplies (SMPSs) have been commonly used in domestic VCRs and TVs, etc for a decade or so, one of the most likely components to fail is the humble electrolytic. The symptoms can be as diverse as a VCR's playback picture swimming in tiny dots, up to SMPSs mysteriously self-destructing. As a service technician myself (though I'd prefer to be a full-time designer!), I was just about tearing my hair out because of the difficulty in determining which electros were faulty and which ones were still OK, in SMPSs and other equipment. I wanted to be able to check electros in circuit, with the power safely disconnected. Why not use a readily-available capacitance meter? Because when electros go faulty, they normally don't lose their capacitance significantly (as many technicians assume they do). Rather their equivalent series resistance (ESR) `goes through the roof'. Capacitance meters don't tell you this; about the best they S can do is give a low reading if the electro is nearly open circuit. About ESR... So what exactly is an electrolytic's equivalent series resistance? Electrolytics depend on a water-based electrolyte, soaked into a strip of porous material between the aluminium foil plates, to complete the `outer' electrical connection to the aluminium oxide dielectric coating on the anode foil. The electrolyte has electrical resistance which, along with the (negligible) resistance of the connecting leads and aluminium foil plates, forms the capacitor's equivalent series resistance. Normally the ESR has a very low value, which stays that way for many years unless the rubber seal is defective. Then the electrolyte's water component gradually dries out and the ESR creeps up with time. The electro gradually acts more and more like a capacitor with its own internal serie