I have been using the truck as it does what I need it for albeit slowly. I have had new forklift engineer out to it and he has replaced pedal switch but says that it is one of the three SCRs breaking down. Is there any way of find out which one is at fault as he has checked with his meter and they are OK but one is breaking down under load. Can this be simulated in any way or do they have to be replaced in turn until faulty one is found?

Thanks for your help