Behringer mx2442a The board has some odd anomalies, and when I checked the power supply, the +17v regulator showed no voltage under load. I changed it, and it still exhibits the same symptom. The voltage is correct under no load. I took the master section out of the board to see if there were any bad components, but it is almost impossible for me to track this down. Does anyone know what to look for? Something is pulling the regulator right down to 0 volts! Thanks in advance for any help!

Hi Bryant...
That particular power supply is hard to come across. There is a brand new one for your mixer on E-bay for $200.00 here:
http://www.ebay.com/itm/Behringer-Eurodesk-150-Watt-Power-Supply-For-Mixers-MX2442A-MX3282A-NEW-/252274097139
Hope this has helped you.

FIlter capacitors in the positive supply are likely failing. These will be the larger metal cans- one may be bulging. Either way, one of them is shorting out after a certain voltage potential is achieved and causing your problem.

Replace the caps in both the positive and negative power supply sections and this should alleviate the issue. Match the working voltage rating, or even one step up in working voltage. yours are likely rated 25 volts, so a step to 35 volts would not pose an issue.

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.

You should find +/-15 volts and probably +12 volts an +5 volts as well as the +48 phantom supply. If only one of these is missing, check the regulator for it... most are three terminal regulators. If the one that is missing has a hot regulator you have a short someplace and this requires skill to locate Probably the fastest way is to use a thermal imaging camera... however I have often used a millivoltmeter to find where the supply drops tpo near zero. Using a "calibrated" finger and search for a hot component on the circuit board can be very effective. Likely one of the surface mounted chips has shorted. Replacing these requires skill so best leave board repair to a skilled repair person as you can easily damage the board permanently.

The C23 part is a capacitor and the 7085 is more likely a 7805 which is a voltage regulator. The regulator is easy to find. For the capacitor, you will need the service manual to determine the value required. The main issue is that the leg of hte 7805 is lifted. This implies that the part was conducting more current than expected. This is an indication that the problem with the regulator is a RESULT of a problem, not the defect itself. I would not suggest replacing the power supply blindly as the root cause may beon another board. Just changing the power supply board may result in the same problem again.

I would suggest a trip to the repair shop to get a detailed repair estimate. The shop shouldbe able to determine whether or not the only issue is the power board.

Also, from the experience I have with Behringer units, the power boards are unique to each model.

Dan

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.

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

That time lag would indicate a thermal problem.

Likely the power supply is a switching type that has some three terminal regulators after it such as 7805, 7815, 7915.

These have thermal protection in them and one may be shutting down.

Use circuit cooler to isolate the part that is shutting down.

A high likelyhood of a power supply problem.

I had a similar thing on a GX110 and it was an electrolytic cap that filters for the 5 volt regulator on the DSP board.

As the DSP starts up, the load on the supply sucked it below the operating point and caused the DSP to keep reseting. The display did flash.

The unit will have to be opened and trpunbleshooting done to find and repair the problem.

This is a wild educated guess.

I repaired a Behringer guitar amp that had a DSP effects in it (BX1200 I believe).

The effects were on a seperate board and the board had its own 5 volt power supply. The filter capacitor for the 5 volt power on the board was UNDERSIZED and it had degraded causing the 5 volts to drop out of regulation, dipping to 4 volts. This caused the DSP effects to fail.

YOUR device MAY use the same DSP OR design.

Check the 5 volt power with an OSCILLOSCOPE to look for dips below the 5 volt operating point that occur at 120 HZ.