Behringer Mx8000 Manual
You have a power supply failure. On any large mixer, when all the peak lights come on and stay, and sometimes the VU meters max themselves evem, it almost always means one of the power rails to the op amps has failed. So check your power supply. But it must be checked under load, you can;t just plug in the power supply alone and measure its output.If the desk is indeed loading the supply, inside ther are large boards making up the whole deal, each can be disconnected from the system to try to isolate which board has the problem. Once that far, a schematic won;t help anyway, each IC has a small bypass cap by it, one of those shorts and you have to track it down, the schematic won;t tell you which one of hundreds is the short. Look at them closely, any have black marks on them?Google for the schematic, and as always, try Elektrotanya. I see MX8000 schematic listed there.
Free downloads.Not all manufacturers distribute schematics to the public, but some of us stand there and curse the darkness, while others light a candle. Does this desk run on propane? I think I'll light the candle.Seriously,+18 volts-18 volts+48+5+12So you think the 18 volts failed? Usually, it's one or both of the LM350T's. However, as Doug pointed out, you could very well have a shorted bypass cap on one of the mixer PC boards. If the IC is bad, it will usually be bad unloaded as well. If you replace them, make sure you use heat sink grease and torque them down snuggly.
What killed most of these IC's was poor thermal transfer due to improper factory assembly.If you have a shorted cap in the board, the easiest way to find it is to 'smoke it out'. I learned this technique right from Behringer's lead tech when I was in Germany for training in 2001. We modded our test PSU with switches for each bipolar rail to supply the unregulated +/- 24V or so BEFORE the regulator, to drive the board. The increased voltage and current delivery snaps the shorted cap right open. If done in a dark room, you can see the flash from under the PCB, then desolder the affected cap, shake it out of the board, and install a new one on the reverse side.
Like I said, FACTORY SERVICE TECHNIQUE. From memory, there are some little caps between the faders that go short and pull down a rail. First, work out which board has the problem. I would then power the audio rails of that board with a bench supply that can shove 3 Amps through the shorted cap. I do play safe at around +/- 18V as you suggest. Just wait for the smoke and crackling sound. This is fun electronics.I have used this technique on a number of these desks.
It used to be a common fault. I am disheartened to find it was factory procedure. I thought I had invented it.I do not have a thermal camera, but if you do, you should be able to see which component is sinking the current without resorting to such violence/ entertainment. Hi JohnI have the original EURODESK 48/24 DUAL INPUT 8-BUS i think this the MX8000 but not sure.The LED for +18v on the top right is out. Most channel signals lights are lit GreenThe Power Supply is reading that +44.8v +16v -15.8 the other 3 pins are 0.0v.I am not sure of the pin outs. I am assuming the center pin is GND.Any thoughts?I can do some repair work (BEE -jetplanes- mostly digital design) Can dBm tackle?UPDATE: IF I measure Pins 6 & 4 using Pin 5 as GND I get -6.6v & -11.6v respectively on PS cable end, un-Loaded.Since Digital would prob have a separate GND then audio, MY voltages are probably fine.
But the Pin Outs would definitely help confirm before bringing it in.Any thoughts. The power supply provides +18, -18, +48 ref the analogue ground and +5 and +12 ref the digital ground.You may have a failure in the power supply. You may have a failure in the desk pulling a power rail down. You may have both if a desk fault has caused the PSU to fail.Check and fix the PSU first. Then if you have a split rail bench power supply power the +/- rails of the desk with that to see if you have a shorted rail.This thread has excellent advice on fixing common faults in both the power supply and the desk in earlier posts.Good luck. Thanks MartinI'm seeing negative voltages referenced to digital GND which I'm guessing is Pin 5, that are close to what you and others have defined as Vout on this supply, only Negative.
Behringer Mx8000 Manual Pdf
Any idea what that means? The tolerance is dodgey too- but I designed mil-spec back in my EE days so +18 was +18v not +16.6v but this is budget audio.Anyway I've read thru the thread and not really sure how to accurately test the supply w/o knowing what its specs are for current delivery. Any thoughts? The power supply provides +18, -18, +48 ref the analogue ground and +5 and +12 ref the digital ground.You may have a failure in the power supply.
Behringer Mx8000 Manual Online
You may have a failure in the desk pulling a power rail down. You may have both if a desk fault has caused the PSU to fail.Check and fix the PSU first. Then if you have a split rail bench power supply power the +/- rails of the desk with that to see if you have a shorted rail.This thread has excellent advice on fixing common faults in both the power supply and the desk in earlier posts.Good luck.Opened Mixer and removed PWR connector to each of 3 inner CH Boards. Put them back one by oneand my +18v is back. Someone else I know had this board & told me to check ribbon connectors.Could that really be my problem, a connection went open? Ever see anything like that?BTW Checked PS and voltages are mostly low +14v/-15.8v (and continues to drop under 8ohm load- load is 25 years old 100W resistor) +44.8v (don't use this Phantom v) +3v +11.2v- def not in MILSPEC but OK for Behringer?Any thoughts.
Afraid to close it back up!