Anyone off to VCF-UK

It's not the dummy load, it's the 'series lightbulb trick'. A filament lamp as avery nice positive temerpature coefficient of resistance. You connecto one in series wtih the HV DC lione to the chopper and run the supply on minimum load. If the supply is OK, the lamp remains cold,low resistance, and does no harm. If there's a major failure. the lamp will limit the current. It probably won't save the chopper transistor, but it will prevent trraces from being blasted off the PCB, and it will certainly save my nerves. They;'re even useful when sorting out linear PSUs. My HP9826 arrived with the mains fuse blown, the LT fuse was OK. I tested te plug-in PSU module on my hom-made test rig, it was fine. Put that back in the machine and applied 20V or so ot the termianls of the smoothign capaacitor (the one strapped to the fan mounting. The machine powered and worked fine, so I knew al lthe logic was OK, All I needed to do was sort out the transformer/rectifier/capacitor circuit. Pulled the PSU again, put a new fuse in, connected a bulb in series with the mains input and powered up with the fan remvoed and the transformer secondary disconnected from thr rectifier. Lamp totally dull, sensible AC voltages on the secondary. Conencted the fan (it's a 120V AC fan running off the transformer primary in this machine), lamp a dull red, fan runs. Connect the secondary wires and try again, this time get a glow from the lamp as the capacitor charges, then abck to dull red . So everythig looks fine, and indeed the machine works perfectly when I remvoe the lamp and refit the regulator PCB. To this day I have no idea hy that fuse was blown But the point is that lamp would ahv eprotected me and the machine from more damage if there had been, say, sherted turns (or a shorted RF filter capacitor) in the transformer. I'd heard 'domestic _lightiing_ applications'. There is a significant differnece, at least for what I do :-) Well, that's a start :-). I iwll have to parallel up 25W oven bulbs or something :-). And fromat what I've heard, it doesn't apply to anything other than mains lighting bulbs, so things like the 24V bulb for my paper tape reader don't come under it. Hopefully muy local electrical wholesaller will keep them (it's the sort of place that doens't ask questions, they just sell you what you ask for). They have a big sign over their trade counter which basically says it's the customer's responsibilty to comply with all the regulations. The sort of place I like :-)) -tony