I have a Behringer DJX900USB DJ mixer in which the power supply failed.
It turned out the transformer primary winding failed. I disassembled the transformer and noticed the thermal fuse embedded in the windings was blown (2A - 250V - 115°C). Since it is a linear power supply, i replaced the transformer with two toroidal transformers (2x15V and 6V) and powered the device up. For about 30 minutes, everything seemed to work fine but then the +15V rail failed.
I noticed both the +15V and -15V regulators have a 1 ohm 1/4W resistor in series with their input. The one in series with the +15V regulator failed. I replaced both resistors, powered the device again and measured the current for each supply rail (all switches on the device set to on):
+15V @ 600mA
-15V @ 600mA
+5V @ 550mA
It is no surprise the 1 ohm 1/4W resistors fail as they have to dissipate 360mW.
I know this is a simple way to prevent damage to the electronics in case of overcurrent.
As i don't know the average current consumption for each supply rail, i wonder whether there still are issues with the device.

So, i would greatly appreciate it if anyone owning a DJX900USB is willing to open his device and measure the current for each supply rail.

 

Edit
My DVM played tricks on me (battery depleted). I measured the supply rail currents again, this time with a fresh battery in my DVM.
+15V @ 510mA
-15V @ 510mA
+5V @ 550mA
This means the 1 ohm 1/4W resistors are pushed to theirr limits as they have to dissipate 260mW.
Should i keep this as is?
I found the schematics for the DJX700. This one is similar to the DJX900. The 900 has an USB interface and slight modifications in the power supply: addition of capacitors parallel to the bridge rectifier diodes and the 1 ohm resistors before the regulators. An original replacement transformer fits both.

 

+15V @ 600mA
-15V @ 600mA
+5V @ 550mA

Is the 600mA the rating of the supply or the actual current? It is typical for a power supply to be used at 1/2 the rated power.

At the university I was told to use a resistor at rated power. In real life I use parts at 1/2 the rated power level.

Because your mixer is used in doors we know the temperature. I build test equipment that gets used in very strange environments. At the South Pole (-40C) the resistor can handle a large amount of power. It is common for some things I designed to be used where the case is too hot to touch. For non-office "things" use parts at 1/4 power.

 

Thanks for the reply. The mentioned currents are the actual ones. My first measurments (600mA) were wrong due to a depleted battery of my DVM. The second (510mA) are the correct actual currents. As the original transformer is custom built for behringer, i don't know its power handling capability, hence my request if someone can measure the currents on an original setup.

Correct me if i'm wrong, but in your reply about the series (safety) resistor, do you mean you use a 1/2W or 1/4W resistor when a 1W resistor is required? So, in this case, if Behringer followed the same recommendations, the transformer should be able to deliver 1A. Probably possible as the voltage regulators are also rated at 1A max.

 

I think Ron means to say, derate the power rating, i.e. use a 1 W resistor when the max power is actually 1/2 W.

 

Got it. When i read his answer again, i noticed my reply was wrong. But i think derating does not apply here as the resistors are used as a safety measure since they are only 1 ohm and need to fail when the current is too high.

 

I should have checked the power rating on the ID label of the device.
It states max. 32W, when i calculate the power consumption:
2 x 15V @ 510mA + 5V @ 550mA = 18W. This is way below the 32W rating.
I was told the 1 ohm resistors could also be there to limit inrush currents so, i will replace the 1/4W resistors with 1W ones and keep using the two toroidal transformers (2x15V and 6V + secondary fuses).