I have a 9 way duplicator that has started to play up (only 5 of the drives burn consistently). I'm trying to nail down the most likely cause - I think i can rule out the power supply as it is the same ports and I think I can rule out the drives themselves. This really only leaves the controller which is a wytron dvd 3000 model.

I've actually swapped the drives around and the bad burns/not recognising media seem to folllow the ports themselves.

All I can tell you about when it actually started to fail my wife was helping me burn some dance concert DVD's and it took 3 hours to complete a pass - obviously one of the burns was bad and it slowed right down trying to compensate. Normally if I'd have been doing a burn and noticed a dud disc I'd have pulled it as the drives start to work really hard.

So is my best bet to buy a new controller? Is it common for these things to fail partially?

Some years ago I ran studios here with a few US duplicator rigs, can't remember the brand but they came with Plextor drives. A few of these failed over the period and we replaced them with the same bought here.

If you're happy with your media, check your drives. HTH Cheers.