How can I correct a fault?

There's a little switch somewhere in the paper path that starts the shredder when you put in paper. It's likely that or the switch is broken.

You might be able to see what is going on looking down the feed slot but you'll probably need to disassemble to get further and that might mean making parts to fit.

I've done it once on a cheapo shredder but eventually I got a new one.

Ehehh
September 2021