Tidying up stuff today. Came across this little circuit from an external case for an optical drive. It never worked... when I eventually got around to trying it. Probably a good couple of months after buying it. At that time, I did something else to get around the problem. Sending it all back was going to be more hassle than the thing was worth. So I put it aside.

Spent a while looking for an integrated circuit I'd bought (for about 40p) for it, only to discover I must have soldered to the board at least a year ago. More hunting, this time in the loft, found the power supply and USB lead. Connect it up on the bench to an old hard drive, and it now works. "Yeah!"

Stick it all into the case, and screw down the lid. Re-test. It doesn't work. "Bugger!" Take it out and re-test. It's working again. "Hmm." Something is possibly being shorted out by the metal case and mountings. Need to try a layer of insulation between the board and those mounting. Some plastic screws too. Just in case. Half tempted to just dispose of the darned thing, for all it's worth!