I have a transformer. It is a custom wound transformer for a old linear powersupply. As is common, it has two primary windings for supporting 115V and 230V operations (or, 120V and 240V as is now more common. the powersupply is old). So, the options are the following:
The owner of this powersupply bought the device in the USA and is now in Europe, so he wants to change the wireing such that this is possible. They desolered the transformer windings, but then got cold feet and stopped, worried they would damage the device (or themselves) if they rewired the transformer incorrectly. It was then handed to me and I now have to make sure it's done right.
However, the transformer doesn't have the wires labled. I wondered, what is the correct way to verify what pins are what coil, and more importantly, what orientation the coil has. It's obvoius in this case what the primary windings are since they were labled on the PCB, and those are the only ones unsolderd. I also know what two pins belong to the same windings with a simple continuity check.
What I'm now worried about is the "orientation". What I don't want to do is this:
I have only limited tools to my disposal for now since I cannot use univerity instruments. All I have is a simple multimeter and an old analog oscilloscope.
I was thinking about applying, with a sound card, a low-frequency (say, 1kHz) signal. Since it is so low voltage, and higher frequency as the transformer is rated for, I expect that the voltages on the secondary would be on the order of milivolts, not able to turn on any of the circuitry. I could then apply this signal to one of the windings. By then using two channels of the oscilloscope, one for each winding, I could see what way the windings are in respect to each other (if I have one connected the "wrong" way I expect a near 180 degree phase shift, otherwise almost perfectly in phase).
Is this a good method? how is this done "propperly"? I would rather not fully dissasemble the powersupply to unsolder the secondary windings as well since this requires me to pretty much take the entire thing appart.