Ian... very good advice above, especially the safety comments from Rick. The power cord goes straight into the transformer for that reason - it is connected to the primary winding and for safety reasons, doing it this way does not expose the mains wiring for you to touch and attempt to kill yourself.Testing transformers....do this with it unplugged from the wall, obviously. With a multimeter, measure the resistance of the primary (ie on the plug pins in this case). You should get a reading of anything from the high tens of ohms to 1KOhm or more, most likely a few hundred ohms. Measuring on the secondary (the two wires coming out of the transformer going onto the small circuit board) you should get anything from near zero ohms up to a few tens of ohms - most likely a few ohms. If either of these readings are very high (over 10Kohms, more likely a meg or more - the winding is open circuit. You will reluctantly have to throw the transformer away. You should also measure the resistance from both windings to the case of the transformer - again you want a very high resistance, especially on the primary.Next measure between ONE wire of the secondary and ONE wire of the primary. You should get a very high reading - a megohm or more. This indicates that the insulation between the windings is goodSo far so good. now plug the transformer in and measure the AC voltage on those secondary wires going onto the circuit board. Be careful here - you don't want to short them inadvertently, and makes sure you are not touching any metal parts or wires (hole only the insulated part of your meter probes. You should get anything form 3 to 25 volts from a normal wall wart - again usually in the middle of that range. if that's ok, leave the transformer on with no load for bit and see if it gets hot. If it does it may have a shorted turn somewhere, in which case the bin is the right destination. (maybe unsolder the circuit board in case somethings shorted on there. You can also measure the DC voltage on the black and red wires - should be around the AC voltage you measures, maybe a bit higher.You can cut the power cord to re-use either the cord or the transformer BUT don't do this unless you know what you are doing. And UNPLUG IT first!!> "I reverse engineer any and all electronics, because I'm not exactly the richest person so I harvest and repurpose components", I've been doing that since I was about 12 (now 61.) It's nice to know someone is carrying on the tradition!You might like my article here: https://www.eetimes.com/author.asp?section_id=36&doc_id=1320904Cheers / David
