Faulty Magnetic Resistance Exercise Bike: Altenator repair

[SpeedBash]

Hope this is in the correct/appropriate forum.

I have a magnetic resistance exercise bike which which has started to make a knocking noise when powered on.

A Google search suggests this is due to a problem with the alternator in the bike:

LiveStrong said:

Some exercise bike models are equipped with an alternator that provides resistance and increased performance. When your alternator is not working properly, it will knock. This normally means it is out of its normal range of 9 to 11 volts. Lower readings indicate that your alternator needs immediate replacement. This is because as you pedal, the electrical current is not circulating correctly and is causing the alternator to work harder and burn out.

Would a garage workshop be able to repair the alternator?

I'm guessing it won't be cost effective seeing as a new similar bike can be had for about £150.