Guys, I wonder if anyone can help. In the last week or so on powering on the mixer. The Effects LED comes on as does the phantom power led if switched on. But there is initially little or no blue power on led and no sound other than a low hum. The mixer does eventually come up after about 10mins if left on, but seems to do so in stages. At first you get the above, then the humming noise seems to increase followed by the main mic leds showing a signal(this hum) continues, but is louder, still no sound from an input source. It then settles down and eventually you get input signal coming through. I suspect PSU going, dodgy cap perhaps, or one of the voltage rails with a cold fault, what do you think guys? Any help sincerely appreciated.
SOURCE: Behringer XENYX 1622FX, won't power on. Phantom power works(?)
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.
SOURCE: What is wrong with it?
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.
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