How to repair something with a power problem?

[grueni]

I'm a complete noob and watched [almost] all Episodes of Dave... He always mentions "Check your power rails first!".

Now I have a problem with a sound system: I've got a Creative: 7.1-Speaker System like this:  http://www.chip.de/ii/37708092_7e6bcc0c63.jpg

In the second I power it on, I hear a loud *THUMP* - and the fuse is gone.
I opened it and looked at the caps - all caps look quite normal.... Everything looks normal.

So now I'm stuck. What are the primary options, if there is a big short in a circuit? Is there a typical way how to debug this thing?
The only idea I had would be to build a 50 Hz 5V/AC powersupply and use it instead of the mains to power the thing - to be able to find the short without breaking a fuse.... But this sounds so silly.

So what would your next steps be?

[teksturi]

Ohms law  If fuse blows, you might want to measure resistance between rail. If there is resistance below what you expect try to find what is causing that. It is usally easy to find what is causing fuse to blow, so this hopefully be fun repair.

[ez24]

Have you tried Youtube?  If you do and find something let us know.  Also maybe you could make a repair video yourself.

[PTR_1275]

Does it have a transformer or is it a switch mode power supply? If you can take a photo of the board, transformer (if fitted) and another photo of the area around where the mains goes in if it is switch mode so we can start pointing out possible failed components for you to test.

I've seen many switch mode power supplies where the switching transistors have shorted causing the fuse to blow. Quite often the fuse will blow before the components blow their case so everything looks ok.

[drussell]

In the second I power it on, I hear a loud *THUMP* - and the fuse is gone.
I opened it and looked at the caps - all caps look quite normal.... Everything looks normal.

So now I'm stuck. What are the primary options, if there is a big short in a circuit?
...
Is there a typical way how to debug this thing?

There are probably shorted transistors in one or more amplifiers but if you can disconnect the amplifiers from the power supply you could check for both positive and negative voltage rails to be sure they are both present and at the proper voltage without the amps connected.

Unfortunately we can't give you more specific instructions without knowing what make and model the unit is and/or having clear pictures of the guts of the unit and the circuit boards, etc.

[JacobPilsen]

The only idea I had would be to build a 50 Hz 5V/AC powersupply
...
without breaking a fuse.... But this sounds so silly.

Rather use lighting bulb (filament lamp) (with approximately same current rating) in place of fuse.
It will not break, just light...