A500 External fdd problems ...

[paul1981]

Nobdy, huh ? Bummer ...

You're Kickstart2 then or 3? Not that it matters that much, but the more info you provide then something may occur to someone. I can't say I've ever used more than 1 external drive, so I can't help you here.
I know drives have write protection switches on them, are you sure they're all in the "write" mode? If they're not then you can't write to them, only read.

How much RAM do you have? Maybe you have a weak PSU or something, and so it's struggling to power all 4 drives in your system together. Do you have anything else attached to the Amiga? Or is it just the extra drives?

[paul1981]

Do all drives show up when you hold both mouse buttons down on cold start/reboot?
Do you have another Workbench disk you could try? Have you tried testing the drives with tools like x-copy or d-copy?

[paul1981]

It's a no go. Tried it with 3rd drive disconnected. The same behaviour occurs. I tried it under wb 1.3 as well. Starts formating the disk, then on the 15th cylinder it says ... please replace the disk. The disk is write protected. I'm clueless ...

Always on the 15th cylinder exactly? Even after multiple attempts?
Maybe there's a bad drive/cable in the chain? Do you get different behaviour with the drives in a different order?
If it failed part way through the format due to a "write protect" failure, then to me that sounds like the write-protect switch needs a clean (in the mechanism). Then again this drive works fine on its own does it? If so then try a heavier duty PSU. I think the floppy drives eat 12V, and 12V is only low current rated on standard Amiga PSU's (designed for floppy drive and Audio circuitry).
Failing that, you could try swapping the Paula chip (controls the floppy drives).