Switch on and observe the LED display. When you start up the Behringer Ultracurve, the LED display shows a status message, depending on the settings. In the event of a power failure, the Behringer Ultracurve automatically switches to "bypass" mode. It sends the input signal directly to the output, without any equalization, or "EQ." This happens so power failure in the Ultracurve doesn't cause the equipment connected to the Ultracurve, such as amplifiers and speakers, to fail as well. Equalization is the act of enhancing and diminishing frequency ranges in a sound. For example, lowering the high frequency and boosting the bass. Newer models, such as the Ultracurve Digital DEQ1024 have a bypass icon which will flash when in bypass mode. Older models don't have the bypass icon, but you can tell if the unit is in bypass mode because all of the equalization sliders are redundant. Move the sliders, if there is no effect, it's likely that there is a power failure.
Investigate the power supply. Unplug the socket from the mains wall socket and remove the screws fastening the back panel and lid to the chassis. Look out for any blown fuses or transistors near to the mains power input socket. Blown components typically have a brownish discoloration. If you spot a blown fuse, unplug it and replace it. Fuses are available from most hardware and electrical stores. If you spot a blown transistor, use a clean soldering iron to melt the solder joint fixing the transistor connector pins to the circuit board. Wipe away the solder residue and solder in a new transistor. Screw the top and back panels back on.
Remove the software. If the software has been affected by a virus otherwise corrupted, removing the software and reinstalling it from the disc loads a "clean" copy onto your computer. The Ultracurve series of equalizers has a software component that enables you to sync it to your home studio. If using a Windows operating system, click on "Start", "Control panel", "Add/remove programs". Right-click the Behringer Ultracurve software and select "Uninstall". If using Mac OS, open "Applications" and drag the software to the "trash" icon. Put the installation disc in the disc drive and reinstall the software by following the on-screen instructions. When you insert the disc, you will be asked if you want to run the installation or save the files. Click "install", then click "run."
Identify damage to the filter caps. These are the small, cylindrical metal components located on the circuit board inside the Ultracurve. If you are still having problems with feedback or unwanted frequencies, it may be due to a faulty filter capacitor. The job of a filter capacitor is to prevent certain frequencies from being amplified. Connect a phone cable between a CD player output and a channel input on the Ultracurve. Connect two speaker cables to Ultracurve outputs and connect those to a pair of speakers. This routes an audio signal into and out of the Ultracurve. Gradually increase the output signal of the the CD player by turning up the "gain" dial. If working properly the filtering function should eliminate feedback. If feedback occurs, adjust the equalization sliders on the front control panel to remove the problem frequency. If it reappears, this is a sign that the filter caps are not functioning properly.
Unscrew the back and top panel of the Ultracurve with a Phillips screwdriver to expose the circuit board. Unplug the filter caps from the circuit board and fit like for like replacements. The specifications are written on the side of the filter. Filter caps are available from electronics and radio repair stores as well as amplifier equipment websites such as Small Bear Electronics at http://www.smallbearelec.com/Detail.bok?.