Trace Elliot GP12 SMX Nover Caps ESR help?

[itek]

I am currently troubleshooting an old Trace Elliot GP12 SMX Bass Head that works great till it warms up, then the volume decreases dramatically. I opened it up and found 2 of these little Nover RE Series 40v 220uf caps that the plastic had kinda melted down. I pulled em out and tested them with an ESR of ~.20 which seems low according to my little "chart". I checked the datasheet at
http://www.anglia.com/product_search...sheet_id=17124
but it doesn't mention ESR... Should I go ahead and post pics of all the boards or start with these caps? Thanks guys,
Jared

[itek]

since you all are so nice here and nobody quoted my dumb "ESR seems too low" statement i'll go ahead and point it out haha, gosh just shows how much i have yet to learn....
anyway i got the bass head running, turned out to just be a loose solder joint on a resistor on the power board. peace!

[lti]

The datasheet does not list ESR because the caps are designed for circuits where ESR is not critical. They are only general purpose caps.

[Longbow]

I assume this device is a bass guitar amp? Do you have the schematic, because I think you are going to need it? When the volume decreases, does it get distorted? Can you hear normal amplifier hiss at any point? The simple steps first, before looking for capacitor problems..

I had a guitar amplifier with these general symptoms recently. Audio output slowly disappeared. The circuit began to oscillate at a couple MHz, wiping out the audio. But you would need a scope to see it and a schematic definitely to begin troubleshooting the problem. Sounds interesting. Any news?

[Longbow]

To address your question about your faulty capacitor and suitable replacements, your bass guitar amplifier almost certainly does not have a SMPS which would require some low ESR filter caps. The entire amplifier runs on general purpose parts. As usual for all audio amplifiers, some attention is given to the prevention of parasitic oscillation; sometimes those damping circuits will involve electrolytics, most of the time they will use ceramic or mylar caps below the 1 uf range. The capacitor shown in the photo is most likely a filter cap on one of the power supply lines. This is where the schematic becomes useful. Not every electronics problem is caused by faulty electrolytic capacitors. But obviously faulty caps must be replaced if they are found.