Scored a Juno-60

[Altitude]

..
I have just built one and I´m testing my stock of electrolytic capacitors...

Do you have a link for the one you built? Now that I am doing more restoration work, that would be a handy tool to have and probably save me a lot of work

[Mooger5]

Sure. By googling images of "ESR tester" a number of schematics appear. Of all, these two http://www.circuitlake.com/capacitor-esr-tester.html and http://freecircuitdiagram.com/2010/05/2 ... nce-meter/ are the easier to build. I built the last one because I already had the parts minus the DC microampere meter. It turns out a VU can also be employed. I had a 30V DC Volt meter which after supressing its internal resistor worked as well.

[Mooger5]

Quick update: out of 200 caps, one has measured a very high ESR and a great loss of capacitance. "EB" brand, 4.7 uF, 100V. Measured ESR: higher than 30 Ohms. Measured capacitance: 870 nF. No kidding. And it just looks normal with no signs of bulging.
Several other caps that were inside a Matrix 1000 measured around 10 Ohms and most presented slightly higher ESR than average. They´re now in the trash bin.

[madtheory]

Great stuff mooger!

[Mooger5]

I was hoping to find some definitive answer, as sometimes I´d think it´s only techie bull, and sometimes not. The Matrix 1000 is about 25 years old and the bad caps needed to go, but the Polysix is 30 and the caps seem fine (regarding ESR). I guess the lesson learned is that you don´t go out on a cruzade against recapping. Case by case sometimes it´s justified. When in doubt, just trust your gut feeling, but hey a commercial ESR meter isn´t that expensive; I just found this one http://clientes.netvisao.pt/greenpal/evb1.htm

[madtheory]

I disagree- here's a very recent example of diagnostics winning over recapping:

http://www.vintagesynth.com/forum/viewt ... =5&t=64517