23-01-2016, 11:52 AM
If least-cost is the goal, a Chinese kit is less than a tenner, and measures LCR, ESR and most 2 and 3 legged semiconductors... But that's cheating 
Not sure which version you have, but I've just checked my 87V - at 100kHz and 0.5V, it's about 1.4dB down relative to 1kHz. That varies with applied voltage - it was slightly better at 5V, and at 20mV it's unusable.
Given that accuracy is not a big deal here, it'll probably be OK (but see below). Basically, it's about indication - when the ESR starts to rise, it does so fairly rapidly (increased ESR leads to increased heating which speeds up the evaporation which increases the ESR). The designs with a hand-calibrated moving-coil meter with a slightly non-linear scale are actually fine for repair work.
Before I got an ESR meter, I regarded PSU repair as "refurbishment". So if there were any signs of trouble, I'd just change all capacitors and any high value startup resistors. This gave me a 100% success rate in the shortest time possible (which mattered in a live broadcast environment). Did I change capacitors that were perfectly OK? Undoubtedly. But they would have started to play up at some point in the future, so it was "preventive maintenance". The downside of this approach was the need to keep a large stock of capacitors, but that's no problem given the other projects we did - same for me at home, too.
I sometimes measured them with a function generator and a 'scope. My old Wavetek can deliver 10V into 50Ω. Feeding that into 0.1Ω (via a 51Ω resistor) gives ~20mV. At the time, I decided that any less current might require attention to detail around noise, but obviously 200mA is fairly hefty for a battery powered device, so I talked myself out of investigating any further. Looking back, I probably gave up too soon...
Based on how my 87V behaves, you'd need some amplification after the cap to get up into the 0.6V range.
Not sure which version you have, but I've just checked my 87V - at 100kHz and 0.5V, it's about 1.4dB down relative to 1kHz. That varies with applied voltage - it was slightly better at 5V, and at 20mV it's unusable.
Given that accuracy is not a big deal here, it'll probably be OK (but see below). Basically, it's about indication - when the ESR starts to rise, it does so fairly rapidly (increased ESR leads to increased heating which speeds up the evaporation which increases the ESR). The designs with a hand-calibrated moving-coil meter with a slightly non-linear scale are actually fine for repair work.
Before I got an ESR meter, I regarded PSU repair as "refurbishment". So if there were any signs of trouble, I'd just change all capacitors and any high value startup resistors. This gave me a 100% success rate in the shortest time possible (which mattered in a live broadcast environment). Did I change capacitors that were perfectly OK? Undoubtedly. But they would have started to play up at some point in the future, so it was "preventive maintenance". The downside of this approach was the need to keep a large stock of capacitors, but that's no problem given the other projects we did - same for me at home, too.
I sometimes measured them with a function generator and a 'scope. My old Wavetek can deliver 10V into 50Ω. Feeding that into 0.1Ω (via a 51Ω resistor) gives ~20mV. At the time, I decided that any less current might require attention to detail around noise, but obviously 200mA is fairly hefty for a battery powered device, so I talked myself out of investigating any further. Looking back, I probably gave up too soon...
Based on how my 87V behaves, you'd need some amplification after the cap to get up into the 0.6V range.
