I just got an MXR carbon copy today (it was $99 on Amazon, which is super cheap). I put a battery in, hooked it up, and plugged it in, but it does not work. The mod switch bright blue light turns on, but the main switch does nothing but switch between no sound and the regular guitar sound. I have the option of returning if for full refund including shipping to the seller. Any other ideas? Am i missing something?

I would check the difference in sound between using an AC adapter and a battery. These things lose the effect when the batteries get low.

I can't see any reason to do that unless the battery gets old. When you plug in the adapter, it automatically switches off the battery.

Usually with volume pots,the ratings dont matter. you can really buy then anywhere like guitar center,micro center and online. they're really cheap and well worth it.

First thing to check is the battery or the adapterr.

First thing to test: Do all the controls vary their function smoothly or does say the volume control vary the output only slightly. If the latter condition exists I would open the pedal and look for broken solder around one lead of the volume pot. The broken solder is hard to see... look for a little grey line on the menicus of the solder filet around each lead. Also look for cracks in the circuit board. Use a bright light.

I don't know what you mean by "DC Brick"...

The MXR Stereo Chorus unit requires a special 18 Volt power adapter. The common 9 volt pedal power adapters will NOT work with this device. If you have batteries in the unit, when you plug in an incorrect adapter, the unit disconnects from the batteries and the caps discharge so the light will fade.

You will need to use: ECB-004 18-volt AC Adapter Best to use the manufacture's exact device for this one.

DO NOT count on a "new" battery to be good! I always carry an inexpensive meter (about $3 from Harbor Freight) to test batteries. Try yet another battery...
A common failure however is that the wires to some of the battery clips break after having to fight with 9 volt battery clip removal that have wires... The ones without wires have a habit of not making contact at time...

Many of those connections REQUIRE using TRS cables (stereo style) rather than TS cables (mono style). It is possible you have mixed the cables if it worked before.

Any cable plugged into an "insert" should be a TRS (tip-ring-sleeve) cable.

Look up these connections in your 1604 manual.

Make sure power voltage is adequate. If using a battery, the LED will light LONG after the batteery is beyond usability.