You should find +/-15 volts and +5 volts as well as the phantom power... but that light can come on at much lower than desired voltage.
Note that the regulators are current limited so a short on the mixer board can kill one of the voltages.... but you are not getting any input from teh switching portion of the regulator so the switching part of the supply is apparently dead. To replace the supply you would have to call Behringer at 1-425-672-0816 to get the part number and an incident number and then call FullCompass which is their part distributor now.
When working on a switching power supply, use an isolation transformer for safety and use a 60 watt lamp in series with the power cord to limit current during testing.
The circuitry will be SIMILAR to the power supply found on page 9 of schematic you can download at:
http://elektrotanya.com/behringer_ub1204fx_pro.pdf/download.html
