Testing electrolytics

[TimJones47]

Hi All,
I have just spent several weeks trying to fix a Fender Rhodes power amp which was blowing fuses, i was convinced the transformer was short circuit as the coil resistances were less than 2 ohms. I finally realised there was a short circuit on the rectification and smoothing board, but there was no sign of any shorts using a meter. Changing all the electrolytics sorted it out but none appear short circuit with a meter. My question is how can these type of faults be tested?

Thanks

Tim

[Conrad Hoffman]

To seriously test an electrolytic you should measure the value on a bridge and note the dissipation factor. If the DF is high, the cap is on its way out, regardless of what the value measures. Cp is also better clue than Cs. You should also do a high voltage leakage test at the voltage rating of the cap. If the leakage is above the datasheet value the cap should be tossed. My guess is the cap(s) were breaking down at voltages above what your meter applies to measure resistance.

[nigelwright7557]

If possible its always worthwhile powering up with just bridge and smoothing capacitors connected to see if fuse blows.