This quick video details how to tell what side of your eurorack module’s power connector is positive using a simple, inexpensive Digital Multi Meter (DMM).
The audio is rather poor, so here are the steps:
1. Locate an IC on the board of the Eurorack module, in this case, an LM13700
2. Google Image Search LM13700 and note the positive voltage pin (in this case pin 11)
3. Using your multimeter in either continuity or resistance (low – in this cass 200 ohms) touch one probe to pin 11, and one probe to either side of your eurorack modules power connector. your probe will show activity on the pin that touches the power connector, and that side will be positive.
As I say in the video, I have only been into DIY electronics for about two years, and am self-taught so if there are errors, please let me know.