Question for electronics techs or engineers?

L

loveroffreedom

New member
I have an SWR Bass amplifier LA series 12. It recently stopped working and just makes a loud hum when I turn it on. After inspecting I noticed the speaker is being pushed out which (correct me if I am wrong) indicates DC voltage passing were it shouldn't’t. I inspected the power amp (power supply) and found a brown stain around a 22 microfarad capacitor. If this is bad it would pass the DC voltage when it shouldn't... correct? SWR was of no help to me, they even emailed the wrong schematics. Thanks for your answers in advance
 
The normal failure mode for an electrolytic cap is to fail short circuit. Replace it and see if that solves the problem. Be sure to at least match the voltage rating and polarity - it is not enough that the capacitance is the same.
 
Had a look at the schematic http://elektrotanya.com/swr_la12_la15_power_amp_sch.pdf/download.html and I can't find a 22?F only a 2.2?F. But to cut a long story short if the capacitor is "crying" it needs to be replaced as even if the dielectric isn't short circuit it may well have a low enough resistance to pass a significant current. Once you've replaced it then you'll have to work out if it's taken any other components with it when it went to capacitor heaven.
 
Replace the capacitor and then retest. The replacement needs voltage and capacitance ratings as high or higher than the original.

If it does not work check for DC coming out of the power supply. If it is AC then replace the rectifier.
 
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