Behringer EuroDesk MX9000 mixer problem - Help!!!

[Molasar]

Dear gentlemen,

Forum newbie here...

I've got a mixer and/or PSU problem that's beginning to make me want to pour out some gasoline on this mixer and PSU and throw a match!

Background facts:

a) Purchased MX9000 mixer brand new

b) 3 weeks later (Saturdays only... about 20 hrs total) PSU gave up and was returned for warranty service

c) Upon return, PSU ran for 3 hours and caused a short circuit, tripping the main wall 10A (120VAC) breaker. Note: This short is present EVEN if the PSU is OFF!

d) Inspected PSU insides. First warranty job was horrid. Badly done. Capacitor (C17) 100uF 35V 85°C(M) is bulged at the top.

e) From local and online advise, replace ALL caps (with top Panasonics) and all 5 regs. Stock LM350-3A regs replaced with premium LM338T-5A regs; stock LM317-1.5A reg with premium LM350-3A reg; stock 7812-1A with premium MC78T12-3A reg.

f) Inspected MX9000 mixer, as a burnt smell came from it.

g) Found out mixer's Output PCB Euro07 PCB (PCB820099RevB) has two burnt tracks (same net, 1 on each side).

h) Carefully removed burnt tracks and even more carefully replaced with tracer wire.

i) Reassembled everything and connected alone. MX9000 and PSU turns on.

Now here's the problem:

Whenever I connect anything to the mixer that is grounded (i.e.: grounded, 3-prong CD player, etc., etc.), NO MATTER if the PSU is OFF, the main wall 10A (120VAC) breaker trips!

I disconnected everything again and the mixer and PSU turn on.

If I even touch the mixer with a 1/4" plug from ANY grounded gear, POP!

I turned off the power strip, turned off the PSU and connected a grounded CD player. I turn on the power strip and POP!

Tried another thing.

I connected a small, ungrounded mixer and everything turns on!!!

So, there is clearly a ground short, even though the PSU is off.

Electrician assessed my electrical instalation and all is ok.

Any ideas?

Someone suggested maybe a rectifier diode inside the PSU was at fault. Can this cause this behaviour?

I made a lot of different scenarios with different equipment and different jacks on the mixer. Final word: If the connected gear is grounded, a big short circuit will result, even if the PSU is off.

What can I check? Could it be the mixer, or the PSU?

Any input welcome!

Mike

[pinkmouse]

Take it back as unfit for purpose and get a refund.

[Molasar]

Can't do that... it's been modified...

Besides, I actually do believe the mod to result in a better PSU than the stock one... (Xunda? caps vs. Panasonic caps)

I actually believe such a serious and big short circuit as this one is actually easy to fix... just need to find it!

Thanks!

Mike

[Eva]

Either pase or neutral are shorted to earth. This short may be anywhere within the power supply, even in the transformer. Is the PSU based in a 50/60Hz transformer or is it swiching mode?

[Molasar]

Yup..

I got it yesterday...


Neutral shorted to earth in PSU.... polarity was reversed in my studio (they were upgrading my installation) and it popped my mixer...

Behringer mistake.... go figure...

Thanks!!!


Mike

[Molasar]

Well, good news.

Mixer is up and running.

Now I have a different problem:

Seems like the main output section inserts are reversed: tip on TRS plugs are in, Ring is out. Not so on the channel inserts, where the Tip is out.

All the main output section inserts are reversed: subgroup inserts, main inserts, etc.

Is this a Behringer mistake too, or did I somehow get the two narrow ribbon cables going to the main output board swapped?


Thanks!

Mike

[geminni]

My Behringer UB1832FX has insrets where the tip is singla out and the ring is signal in.

[Molasar]

Ok...

Swapped the two thinner ribbon cables going to the output board inside.

Problem fixed. Tips are now sends.