Wow, thanks John and Irving2008

Before I blow the dust off my GCSE electronics certificate (grade B - long time ago!), I will give Roy's suggestion a try when the part arrives. If it works, I will upgrade to a higher voltage capacitor as you suggest. I still remember seeing a capacitor explode when it was deliberately connected the wrong way around, as a warning, so am cautious about higher capacity units in general.

If it does not work, I should give Roy the chance to swap the power supply for another unit if it is genuinely faulty. If that is still no good, then I will take you up on the offer of helping me make my own linear supply. I have ring terminals and an electricians crimp tool (proper heavy ratchet job, not cheap DIY one), and with a couple of questions and a diagram could probably put one together.

The system 3 board is technically rated at 24v-30v, although Roy does allow 33v to give a bit more motor power. Anything higher is probably pushing it, and so the above specs might need to be revised a bit. Could I add a voltage regulator (?) or start with a different transformer?

If I do end up making my own, I'll signoff from this thread and start another.

Thanks
Barry