Forget your multimeters for a quick easy way to determine polarity & voltage buy a cheap automotive LED (we all know what LEDs are right) Tester . The kind that lights up Red for a positive feed & green for a negative. Simple no more juggling a multimeter under the benchwork or smashing scenery while trying to find that fault. One caution just beware that dark current doesn’t lead you astray these tester can be very sensitive and will light when even a very low voltage is present.
What’s it do on DCC? Fred
Good question. If DCC is really a continuous set pulses with alternating polarity (ie square wave AC) then the LED should alternate colors. This may happen so quickly that it appears to display both colors at once. I don’t have DCC yet so can’t check.
It would at least tell you that voltage is present but you’d need a dual trace oscilloscope to determine phase relationships.
Forgive my ignorance but I have never worked with DCC but I would suspect that it is just DC current overlaid with a coded carrier wave carry instructions to the module you are controlling. So I see no reason the LED test light would not work as per normal. if you were just testin the basics then you probably wouldn’t have a control working at this time anyway. DCC must be similar to automotive CAN comunication?
No, with DCC you have a rectangular wave with a 50% duty cycle (unless you are running an analog loco at the time, which would stretch the time for one side). So the led would probably look yellow, or something. Now, if you were running an analog loco on address 0, you should get more one polarity than the other, and you could probably see it. Another option for testing polarities would be to completely disconnect the DCC booster from the track, and hook up DC to the bus, get everything right, and then remove the DC and put the DCC back on.