My #2 sad story I built a CD switch machine power supply per Peter Thorne's book "Practical Electronic Projects for Model Railroaders", chapter 5. It worked fine until I fried it one day when I shorted something while wiring up an other switch machine. I bought a 2nd home-made one,(someone said it was actually made by P. Thorne), but I fried it too - same cause! Right now you're probably thinking "the best I can do for this fellow is to suggest he take up slot car racing & leave MR to competent people". Please bear with me. This is the first time i've been abletovent&Ihaveallthesequestions&people actuallyanswer!Sorry, lost it there: OK now. Questions: 1. How do I test capacitors, transistors & diodes to see if they are still functioning? All I have is a multi-meter & limited electrical knowledge. Duuuh, there's a surprise! 2. Are these switch machine power supplies available commercially? 3. If I get/make another one, is there some way to protect it against electrical mistakes, maybe by adding more diodes? 4. Is there any alternative? (I don't think I have any alternative; I feed all my sw machines with bell telephone wire. "Regular" current from the power pack doesn't work. I presume it's because of the tiny wire & long runs). PS thanx to all for the answers to my earlier post. Much appreciated.