The idler tyre is a small but crucial part of the ALF03 Data Recorder mechanism. If the idler tyre is worn or broken, the tape will not be pulled past the head at a constant rate (if at all) which results in very poor loading performance and / or "chewed up" tapes.
I have serviced many ALF03 units over the last few years and a damaged idler tyre and idler tyre failures are starting to become a more common problem. It is an age related issue as the idler tyre rubber degrades naturally over time causing slippage (which isn't improved by changing the cassette unit drive belt), and eventually total breakage.
Early symptoms usually show up as "tape slipping", which is characterised by "tired sounding" loading tones from the speaker when loading games as the tape slows, then speeds up again.
Sometimes, small gaps are visible in the tyre, or the tyre falls off completely and you find it inside the case (see photographs).
The idler tyres are very hard to find now and these are from a brand new trial batch we had specifically made.
They have been tested extensively and work perfectly.