This is an AC adapter for a guitar effects pedal. At the location where the wire connects to the block, the plastic was torn off, exposing the copper strands inside. I did my best to cut off the plastic to expose the 2 inner copper wires. I plan to resolder them and apply heat shrink tubing.
However, the problem is there are no colors to indicate which wire connects to which wire, since the 2 inner wires are covered by the same black plastic. What can I do to confirm the correct connections? If I just guess and connect wires temporarily with alligator clips, and plug into a guitar effects pedal to see if it works, would this risk damaging the pedal if I guessed wrong?
Well lacking a multimeter to determine polarity there is always the old tried and true potato indicator. Extend each wire a little. Nice to use a few pieces of copper solid conductor. Push both wires in the piece of a potato.
Easiest: Test Polarity
Gather two, 6-inch-long plastic-insulated copper wires, a D-cell battery, a potato, tape, a knife and pair of scissors. Use the scissors to strip about 1 1/2 inches of insulation from the wire ends. Position the battery on its side. Tape one wire to the battery’s positive side and the second wire to the battery’s negative side, which is flat. Slice the potato in half. Insert the stripped ends of the copper wires into the potato’s flesh at a depth of at least three inches. Observe how the electrons that flow out of the battery’s negative side and through the wire into the potato turns the potato green. Watch for bubbles that form in the potato next to the wire end attached to the battery’s positive side. Consider how the potato acts as an electrolyte, which conducts an electrical current between positive and negative polarities.
Worked for me 60 years ago as a kid and potatoes haven't changed.
Oh, I just noticed that diagram. Does it mean the outer ring is hot, and the inside is ground?
I do have a multimeter. I tried testing in a similar manner as shown here, but I put my multimeter to measure DC voltage at the highest setting possible. I did not get any reading from the 2 wires.
That is ridiculous. Set it to any range close to what you are measuring. You cannot harm the meter, unless you exceed the meter rating, which is likely 300 volts or more.
Adapter is connected to brown extension cord, which is connected to a power strip. The 2 unidentified wires of the adapter are connected to yellow and green alligator clips. Here, the wire with the yellow clip is connected to red probe of multimeter. Black probe of multimeter is connected to a ground hole in the power strip.
Your setup looks to be correct. My best guess is either the wires are shorted or the adapter is dead. On the bright side a 9.0 VDC wall wart is not expensive at all. A Google of 9 Volt Adapter or 9 Volt wall wart should bring up a dozen or more hits.
Also make sure the connector is the same size. That type plug comes with various combinations of inner and outer diameters, as well as different lengths (I think the manufacturers intentionally keep coming up with new connector sizes just to make it difficult to get a compatible plug from anyone else).
Why? Don't you want to measure the voltage of the power adapter? If so, why not use the blue wire that is clipped to the second lead of the adapter? Then you can actually measure the voltage output of the adapter and decide which wire is = and which wire is -. The sign on your meter will tell you is the RED lead is connected to the + adapter wire if the meter shows +.
Paul
Did not see that - definitely wrong. On that type adapter there should be complete isolation between the AC side and the DC output. Notice that the adapter does not even have a ground pin, only the hot and neutral, and those pins are not polarized.
Got it. I have done as suggested and measured +9V with one wire to yellow clip to red probe, other wire to green clip to black probe, confirming the wire with yellow clip is the hot wire, to solder it to the wire connecting to the outside ring of the plug.
Glad you got a solution but the terminology is wrong. Neither wire is the 'ground' or the 'hot' wire. One wire is positive with respect to the other by about 9V, that's it. For one wire to be 'hot' the other would have to be designated ground, or better still actually connected to ground (the muddy stuff outside), but neither wire is. Positive and negative are the appropriate terms here.
