---Original Message----- From: Mike To: PICLIST@MITVMA.MIT.EDU Date: Monday, 11 August 1997 16:49 Subject: Another Power Supply Issue - reliability thinking >At 01:48 PM 8/11/97 +0930, you wrote: > >>>No way - I know how they make these switch mode supplies and how the >>>transistors are treated prior to and during assembly - I wouldn't risk >>>the fire hazard. I've seen one go up and that was enough. I'd rather >> >>The power supply in mine has been running for about 3 years, more or less >>continuously. Monitor is green, so it powers down and eliminates bulk of >>the kWh. IMO, if it was going to fail, would have happened in first few >>months; a la bathtub curve. All thats likely to happen now is a mains >>fault, and I've got some heavy iron taking care of that... One good idea is >>to revers the fan and filter it, but make sure you clean the damn thing >>monthly or less. > >No. What you seem to be operasting from is a sort of faith - best held in >terms of a dogma. I do not have such misplaced hope in the reliabilty of >electronics - we are realists aren't we ? > >And you don't know when the other end of the bathtub curve will hit and >the bathtub curve is not 'L A W' it is only of statistical relevance and So there's a 1 in 10 million chance it will cause a fire. I take greater risks than this crossing the road. Thats just a figure I plucked from the air - who knows what it really is? A MTBF (catastrophic mode) would still only be statistical. >bears little relationship to those random faults that can be traced back to >the way devices were treated during manufacture. Hewlett Packard did some >major report on this - anyone know where this is on the web ? > >Would you want your house at risk because you hope your PC won't start >a fire because you have faith that it worked for 3 years 'therefore' it >won't fail catastrophically !?! Thats the sort of thinking that caused If I believed it wouldn't happen I wouldn't insure. But I do - against the 1 in 10 million chance. I also have earth leakage circuit breakers installed for the same reasons. And a smoke detector - becoming mandatory here. >the Shuttle debacle in which 7 people were killed - I might add it was a >heck of a bad management decision by nonengineering people. That's a high profile example - similar incidents which kill far more people are happening every day. Aircraft disasters, ferry overloading, bad design of alpine resorts (local to oz - recent), not to mention the 100's of car accidents that are caused by mechanical failure. > >Rgds (And yes I always wear seatbelts) > But do you turn off the following when leaving your house - VCR, clock radio, TV, microwave, hifi, fridge, freezer(ouch)? These all operate whilst in 'non-attended' mode. Some would be a PITA to turn off every time you left for a short duration - some not really possible (deep freeze) They all pose a risk though. MikeS