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Powered Subwoofer keeps blowing fuses

Hi. I have a Klipsch KSW12 powered subwoofer from a home theater system that keeps blowing fuses as soon as it's turned on.

It uses 1.25A 250V slow blow round glass fuses, and at this point I need about 50 of them to even troubleshoot.

I've removed the amp board from the back and I can't see anything obviously burnt or wrong. Most of the heavy connections are completely coated in thick brown glue or something, and I've heard that they love to use that and it tends to short out as it gets older.

I have a working knowledge of electronics and some basic tools (VOM, soldering pen, etc.), and I'd really like to repair this myself if at all possible, but I have no idea where/how to approach it efficiently and safely.

Thanks for your time and help!

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Hi @begreat

Disconnect any power from the sub woofer and then connect the DMM (digital multimeter) in Ohmmeter mode and measure the resistance between the 2 input power wires. Do this with the power switch on the woofer in the operated position

It should not measure 0.00 Ohms which is indicative of a short circuit. The primary winding of the power transformer may have a low resistance (which may be normal) so don't confuse this with a short circuit.

Without a schematic it will be difficult but if there's a s/c on the input you will need to trace the wires from the input connector and see where they go.

Usually they will connect to a fuse and the power On/off switch and the power transformer.

There may be mov (metal oxide varisters) and capacitors wired in parallel across the input so you may have to isolate them i.e. unsolder, one at a time and check if the short is still there or has gone.

If it disappears when you remove a component, measure it in isolation to see if it is the problem or if perhaps it leads to somewhere else that is the problem.

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