Following are the steps to troubleshoot possible power issues. 

1.  If you are using the 18V Power module, make sure it is plugged into the wall and turn it on.  The on/off rocker switch should have a light in it, and the Channel A and Channel B LEDs and meters should come on.  If the LEDs and meters don't come on, check the (3) fuses to make sure that they aren't blown.  If the fuses are good, try plugging something else into the wall outlet to make sure you have power at the outlet.  If you have power at the outlet, the fuses are good, and the LEDs and meters still do not come on, turn off and unplug the 18V Power module.  It needs service.  There are no user-serviceable parts in this module.

The filaments in the fuses are thin and difficult to see.  You may not be able to tell if they are blown or not.  You can try a new fuse of the same rating, or test the fuse with a multimeter.  Most multimeters have a continuity test that beeps if there is a connection.  Or you can check the resistance between the two ends of the fuse.  The resistance should be very low, near 0 ohms, if the fuse is good.  It will be high/infinite if the fuse is bad.  It will most likely be the main/input fuse that is blown if there is a fuse problem.  It is normal for that fuse to blow once in a while due to the type of transformer used.  When it blows, it will normally do it immediately when you turn the power on.  Use slow blow fuses for the main fuse.

2.  If you are using a third party power supply, follow its instructions for troubleshooting.

3.  If your power supply (18V Power or third party) is good, connect a power cable from it to your module(s).  If you are only having problems with one particular module, only connect that particular module to the power supply.  Make sure the power supply is plugged in and turned on.

4.  The DC power LED on the back of the module should be lit.  If it is not, check the power cable to make sure it is good.  You can do that with a continuity test on a digital multimeter.  Or try the cable with a module that you know is working.  Or check for about 18V DC on the connector using a meter.

5.  If the power cable is good and the DC power LED is not lit, the power LED may be burned out.  Switch the module on/off with a footswitch or the override switch.  Did the LED status indicator(s) on the front panel come on?  If they did, then the DC power LED may be burned out or disconnected.  You'll need to remove the enclosure from your rack and remove the bottom panel of the enclosure to check if the DC power cable is disconnected.  If it is connected, but the LED isn't lit, it probably needs to be replaced.  You can get a replacement LED cable assembly and replace it yourself easily.  You can also try a different power LED cable, or temporarily plug the front LED into the connector for the power LED to see if it works.  If it works, then your power LED is probably bad.

6.  If the front panel status LED(s) did not come on, then the front panel LED(s) may be burned out or disconnected.  Check to see if they are disconnected by removing the top panel of the enclosure.  It is is connected, then connect the audio cables to the module and try it.  Do you get sound through the module?  If so, then the front LED(s) probably need to be replaced. 

7.  If there was no audio, then something related to the power board for the module is probably wrong.  The most likely problem is a cable from the DC jack to the board or from the power board to some other board (or a power jumper between two boards) has become disconnected.  Remove the top or bottom of the enclosure to check for this. 

8.  If none of these steps find the problem, then the power board may have a problem.  It is also possible that a power cable isn't making a proper connection somehow and may need to be replaced.  At this point, you could try swapping some power cables with a module that works properly and see if that solves the problem.  If it does, there is a defective power cable.  If it does not resolve the problem, then a new power board may be needed.  Power boards can also be replaced by users without soldering.  It isn't recommended that you try swapping power boards with another module.  There are many different power board configurations that are specific to different modules and module configurations.  Using the wrong power board could damage other boards in the module.  There is also a low probability that the DC jack is defective and needs to be replaced.  You could try swapping the DC jack for one from a working module to see if that is the problem.

The most likely causes of power problems are blown fuses in the 18V Power module and disconnected (or incorrectly connected) power cables, either to the module or inside the module.  LEDs last a long time and aren't likely to be burned out.  Power boards are meant to fail to protect other boards under extreme circumstances, but they will take a lot of abuse before they fail.

If you need to remove a panel to check internal cable connections, be sure to follow the instructions for shutting down the 18V Power module, draining the capacitors, and unplugging it before you open the enclosure.