Behringer BXL 1800A will not come on; main fuse is ok. What is the cause?

If you overload them the output MOSFETs fry and tend to take the circuit board and a few resistors out. They are fixable but it's a pain hat the board fries. The tracks need building up with wire so they can carry the necessary current (or any once they fry). Apart from that they are a decent Amp for little bucks and sound pretty good. They'll need micing for anything but smaller venues but the functions are really useful in getting a good sound for the buck.

Did you check that F1 (red arrows)?. You must open the aluminum cooling in order to find the fuse F1, because it was on the inside, not visible. Usually one of the causes of rupture F1 is one or more diodes (d4/d5/d6/d7) is broken. Check and measure the diode. May also occur, F1 break up just like that, without any other components that causes. This can happen when we open a high level for a long time. It is designed so that the final transistor (which is expensive) not be damaged. Hope it helps.

Hi,

Looks like the power module went out, could be either LM3886T Power IC or Mosfet Module But certainly is in the output stage where your problem is, hope this helps to troubleshoot the issue at least...

That sounds bad! I haven't heard of a runaway supply for these... Testing of the power supply is in order. The LED's are all driven from the +15 volt supply which is secondary regulated by a three terminal regulator... probably a 7815. I have seen failures of this chip in another Behringer product so it may be a bad batch. The question now is if this has fried the main switching power supply.

Behringer is stingy about schematics... however here is one for their DJX700 which MAY have a similar power supply to yours:

http://elektrotanya.com/behringer_djx700-professional_sch.pdf/download.html

Scroll down to "get manual" and click to download... IGNORE other download links.
On page 9 near the lower right corner is the simple power supply, minus the transformer but showing the rectifier diodes, filter caps, and the three terminal regulators. These regulators have a thermal shutdown feature so if they seem to run VERY hot they might cause your problem. Common things are failing electrolytic filter caps. Behringer also uses switching power supplies in some gear and I have schematics of examples of those as well... but peak in your unit and see what type supply you have.

Transformers rarely fail... you wasted money on that... Likely one of the rectifier diodes/module or filter caps has shorted. Continued use will burn out the transformer. It is humming because it is overloaded with failing components.

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.

The fuse blows because of a short in the Power Supply. The power transformers primary windings are probably shorted. next in the chain would be a bridge rectifier or a quad of diodes forming a bridge rectifier with a couple surge diodes off of the filter caps. so if you can disconnect the power from the amp, on the power tranny disconnect the primary wires ( the input AC power wires) usually white and black and take an OHM reading with a mulimeter accross the white and black wires. you should get a reading of 15 ohms or higher up to 30 or so. if so the primary windings are good. so then check the secondary (output windings) red and red yellow, etc. ohm reading and you should get a relatively low ohm reading 2-6 approx. if so its a good tranny. on the primary side if you get a real low reading for ohms , like 1 or something, its toast. once you rule out the tranny, switch your digital mulitmeter to read diodes (in the ohms area looks like a diode symbol (a line and a solid triangle with the line being at the tip end of the triangle). desolder one leg of the diode and put one probe on one side and the other probe on the other side. it should only ring out in one direction. you will be testing approx 6 diodes in this power grid on the pcb. you can also desolder the filter caps after you safely discharge the voltage with a 1 ohm 1 watt resistor to ground and use an analog volage meter to see the needle rise in one direction and not in the other (switching the test probes from one side to the other on the cap). usually what i do is just spend 20 bucks on all those parts from mouser.com and instead of desoldering to test i desolder to replace with new. diodes usually part number 1N4003 or 1N4004 somewhere in that ballbark. hope that helps. i think its your power tranny primary winding that is shorted, be aware that this might domino effect into the rectifier and caps, so expect to replace them. its super easy!! you can email me from my website yostamplifier.com

either that or bad solder joints

Make sure the three position slide switch is set correctly for the stereo usage, that is NOT the bridged OR the Mon mode.

MAKE SURE the pan pots are set to middle as they control the spit of the audio to the two channels.

This is a class "D" amplifier (switching) and there really isn't any fuse for a single channel.

MAKE SURE your speakon connections are good by swapping your speaker cables.

I repaired my unit and had to do that without schematics... Behringer will not give them out. Mine had a severe arc-over on one side power amp taking out about ten transistors and diodes and one swithcing regulator chip. Had to cut out the "cancer" of the burned board.

This unit uses a complementary output stage that is made up of one transistor on one side and a pair in parallel on the other. This drives the inductor/capacitor filter... I think the switching frequency is between 100KHz and 1 MHz as I recall. All those transistors were gonzo. It also fried the main power switching transistors in the power supply, several smaller transistors, diodes, and the switching regulator chip.
Also two 10 ohm power resistors were fried. They soft start this unit by charging the main caps via two resistors that limit the inrush current.
A small switching supply has to come up first before the main supply which sends the DC to the amp section.