BEGINNER getting started (Was: Diagnosing and Reparing Commo

AS I think I said, there is no real 'right' or 'wrong' way to look at this. There are many people here who do design, constrruction, reparis, etc. And we all do it differnetly. All each of us can say is waht works for us. Anyone else can read what we're all saying and decide which bits they like. The correct procedure, I beleive, is to measurew a known live point, then to measure the point you want to work on, then to measuer the live point again. Only if all 3 readings are as you expect do you start work. Even that's not infallable, but it's better than assuming the meter is OK. A firend of mine has a voltmeter for checking 11kV (andn maybe 33kV) overhead lines. In the carrying case is a little EHT PSU (perahps about 10kV), powered by batteries. The proedure is to measrue that, then the line, then the test PSU again. That is very true... The whole issue of 'ground' or a common voltage reference point is a lot more complex than it first appears. Don Vonada said 'There is no such thing as ground' :-)_ To me that statement has 2 meanings. The first is that you can take any point you like as your reference to measure votlages with repsect to. In some systems it makes sense to take different reference points for differnet parts of the circuit, the obvious common example being an SMPSU where you would take the so-called 0V output terminal as nthe reference for votlages on the output side of hte isolation barrier but the -ve side of the maisn smoothing capacitor for votlage aroudn the chopper on the maisn side of hte isolation barrier. Be careful that in the latter case there is a considerable voltage between that refernece point and mains earth amd you can't connect (most) 'scopes directly yo it. The second meaning is more subtle. It's the fact that any connection -- any bit of wire, PCB track, etc has impedance. At high frequencies the inductance of a bit of wire becomes imporatnet. So you might have 2 poitns that appear to be connected together by a nice, solid, PCB track and still find a ripple on one wrt the other. Ths 'groudn bounce' is a particular provlem with high-speed digital electroncis. Sure, I was just trying to provide some. Covnersely, having dedicated screwdrives for the common sixes can encourage you to just pick up the right tool, whereas picking out the corret insert bit and putting it in the holder is more work and you mare feel 'Aarn it, I'll use this little flat balde scrrewdriver jamped across the slot to get this Phillips screw out'. I have a mixtrue of dedicated screewdrivs fro common things (flatblade, Phillips, Pozidriv) and interchangable blades or bits for things like Allen hex and all the security screws. [...] Im my case, yes :-) Of course. If you know that 99% of the time the fault you're seing is caused by a particular component, you do start by checking that :-). But as they don't work _all_ the time, I prefer to teach people the absolutely genral methods of logically tracing faults. When you can do that, you know enouyh to find the stock fault lists, and waht to do when they don't help. Sure. AS I said in my very first mesage, in all fault repair (this doesn't just apply to computers, or even to electroics, IMHO it also applies to things like medicine), there are 2 distinct stages : 1) Finding the fualt -- how to make and interpret measurements, etc 2) Putting it right -- using the tools to replace the faulty component. You will ahve to learn how to do both. It's a great pity that this sort of thing is rarely taught any more. I meet very few people who can get a set of facts and reason logically from them. -tony