[cathoderay57]

Thanks to David for the explanation of how the thing works and to SiriusHardware for the update. Since the thing is so complex, doing any diagnostics with it powered up is frankly beyond me and my test equipment. Therefore, my plan is to replace virtually all of the electrolytics (except the 3 large 100uF 450v main smoothers for now) and see if it will then work on load. If it still fails to run on load then it would appear either there is a fault on the motherboard that is taking down the supply or something in the protection chip circuit has failed causing it to wrongly detect a fault condition when there is none. Cheers, Jerry