+48 volt in power supply is not working. All other voltages are present

It may be a broken solder joint. It may also be a capacitor in the power supply is failing, but a bit less likely.

Pull the chassis out and look closely for any breaks in the circuit board. If none are found then look at all soldered connections, or better yet- reflow each one.

Power it up outside of the case and if it cuts out again, check for voltages at the finals, You should be close to 48 volts from chassis ground to the high side power rails of the finals. One positive polarity with respect to ground, the other negative. You can measure the voltage at the 2-4700 microfarad filter caps. You should see about 48 volts across each cap. If voltage drops on one side, check the cap visibly for leakage or bulging- replace it if either condition is found..Also check for 16 volts at each of the 50 microfarad caps nearby for the same scenario.

Also clean the controls if that has not been done yet either.and look how they are soldered to the PC board. .

I assume you are refering to the 48 volt Phantom power? check rectifiers, filter caps and the regulator. Find if the voltage is getting to the regulator.

You should find pwer supply voltages of +/- 15 volts going to most of the op-amps.
You should find 48 volts for the phantom power source.
You should find 5 volts for the FX DSP or any other logic circuits.
You should find a +12 volt.

Here is a manual close to your unit (yours is an expansion of it):

http://elektrotanya.com/behringer_xenyx-1222fx_v1000_dpm5m_ub-spsu2_sch.zip/download.html

This makes no sense... 32 Watts and 12.8 volts... something to do with this speaker that is rated at 500 Watts???

If you are trying to calculate something for a car amp you don't understand how they work... that is the only thing I can think given the 12.8 volt thing you stated. Most high power car amps BOOST the incoming battery voltage up with a switching power supply. For instance, they might boost to 48 volts and that applied to a 4 ohm speaker would be 12 amps PEAK maximums. BUT the RMS power is one half that or about 288 Watts in round figures before considering losses.

Many car amps are designed to run with 2 ohm speakers... JUST SO THEY CAN CLAIM massive power values in their ads so you will buy them!

The mixer portion requires + 5 volts and +/- 15 volts and +48 volts for the Phantom power for condenser mics.

The phantom power is used for condenser mics. MAKE SURE you do not plug in other mics or devices that do NOT have balanced, isolated outputs as they will short out the phantom power to others.

You should find between 15 and 48 volts between BOTH pins 2 and 3 of each mic connector when measured to pin 1 of the connector. There is about 6K ohms impedance from the phantom supply to pins 2 and 3.

IF you have an accident and connected high voltage to pin 2 or 3 it COULD back up and blow the bypass cap for the 48 volts.

Please note: ALWAYS power ANY interconnected equipment from teh SAME receptacle to avoid damage due to ground bounce in the event of a fault in a piece of equipment.

This MAY be a power supply problem. We need to find if the power supply is putting out what it is supposed to. Using a meter, put one probe in pin 1 (ground) of one of the mic connectors, say channel1. Put the other probe in either pin 2 or 3 of another mic connector... Note we are using different connectors as there often isn't enough clearance for the probes in the same one... With Phantom power turned on and LED +48 lit, how much voltage do you read? If it is say 40 volts or more, then power supply is operating.

If the supply is operating then a POSSIBLE problem is a connector has fallen off where it connects to the supply or the main board.

The power supply provides several voltages such as 5 volts, 12 volts and 15 volts of various polarity.

If the 48 volt supply is found to be operating with the above test, then since the switcher and transformer are shared, it is likely the other voltages are available.

CAREFULLY open the unit and look for a loose cable.

PLEASE NOTE: This is a switching type power supply and part of the supply runs at power line potential. Only work on the supply if you are skilled and have an isolation transformer for your own safety.

The schematics don't show this, however reverse engineering this there are two windings... one is for the phantom power of 48 VDC... this winding needs to provide about 55 to 60 volts DC to the 48 volt regulator. EXPECT around 40 to 50 volts AC on this winding to the full wave bridge of D1,2,3,8.

The +/- 16 volt power regulated by LM317 and LM337 regulators will likely require about 20 volts DC into the regulators. It will be less than 25 volts because there is a 25 volt cap filtering.

Given a 20 volt DC from the diodes D5,6 and diodes D4,7 the transformer will be around 15 VAC either side of the centertap.

A minimum would be 12.5 VAC and say 18 VAC either side of center.

You should see near pure DC across C1 and C2 with only a little ripple of 2 volts MAX. The ripple should be 120 Hz. An oscilloscope is your friend in this area !!!

After reviewing the schematic, I don't understand how the Phantom power can REMAIN on with the power switch off... this CANNOT occur except for what energy is left in the 48 volt supply filter cap... This might last for minutes after the fuse went... UNLESS you have devices connected which are backfeeding the 48 volts. (which would be a disaster)

The 48 volts, +/- 12 volts and +/- 15 volts and the +5 volts ALL come from the SAME switching power supply. I suspect one of the filter caps went or the primary switching regulator a TDP245Y chip.

You should ONLY work on the line side of this using an ISOLATION transformer since the line side has lethal voltages.

To do testing, one replaces the fuse and puts a 60 Watt light bulb in series with the hot side of the inout line. The lamp "acts" as a resetable fuse and limits the current for testing. When all is well again, the lamp will remain out with the power flowing through it.

The D1 diode bridge and C7 input rectifier and filter are first things to check. You can do those with an ohmmeter.

I will caution you to ALWAYS power any and all equipment from the SAME power source. Plugging in devices from across the room will set up ground loops and any ground fault will fry equipment.

If you lucky, the power jack may be at fault since it switches from external to internal battery, but most likely the internal supply is what's damaged... IC regulator possibly. A quick voltage check with a volt meter at the power leads on the main board will verify battery or xfmr supply voltage, if voltage is present then look in close proximity for an IC regulator and check for an output.