Yeah that's the only guaranteed way to find them I've found. There's a couple programs out there that do exactly that. Just start writing files to the SD card a

Yeah that's the only guaranteed way to find them I've found. There's a couple programs out there that do exactly that. Just start writing files to the SD card and read then read them back. I think they should be a bit more intelligent though, seems like right now they write the whole value you enter as the stated/test value then try to read it back, seems like you could detect bad devices much sooner by doing smaller read tests at set intervals.