Behringer MX 1604A Mixer getting hot

[David Schwab]

I have a Behringer Eurorack MX 1604A Mixer I bought about 9 years ago. I mostly use it as a headphone amp/monitor mixer in my home studio setup.

Recently I noticed the smell of magic smoke, but couldn't tell where it was coming from, but then a coupe of days later I noticed that the area on the mixer right above the headphone jack (where the logo, voltage regulators, etc., are) was very hot. The mixer was still working. So I powered it off, and let it cool down, and powered it back up, and as I expected that area got hot again.

It was warm enough to be uncomfortable to touch. I didn't try powering it up with the case open, but I'd expect that part might get visibly hot.

So I powered it down and after it cooled, I opened it up. No easy feat with all the knobs, screws and nuts that need to be removed!

I can see where there was smoke in the case, and one of the three voltage regulators (the one on the right side closest to the corner when looking from the top) has a brown spot under it on the circuit board where it had gotten hot. The part itself does not looked burned.

So, my question is; would replacing that part be enough, or should I expect that it either took some parts with it, or was triggered into failure by other parts? The diodes and electrolytic caps look OK, but one of the caps might have a slightly swollen vent cap. I'd imagine it could stand to have some higher rated parts in there.

Any one have any experience with these mixers or a schematic?

I could just replace it with a headphone amp, but if it just needs a new regulator, that would be cheaper, and it does still function.

[Enzo]

SO fire it up. What voltages are coming out the regulators?

Regulators cost about nothing. Replace them on general principles.

Clearly the unit works overall, but it may be the regulators are working fine, buit something is drawing too much current. let it run long enough for that area to get good and warm, then feel the tops of every IC on the board. ANYbody hot?

If any caps are bulging, replace them, caps are also cheap. The thing has worked for 9 years with the old rated parts. I doubt they failed now because they werer under rated. it won;t hurt to have 105 degree caps, but I don;t think it is necessary.

You can throw $5 worth of parts at this thing and replace most everything you have mentioned. Try that and then worry about if it needs something more.

Schematics are not generally available, and I cannot send you one.

[mozwell]

Hi David
Check out Audio Behringer : Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
There is a schematic for MX1602 there, the power supply should be similar.
It may be the 48V phantom power regulator causing your issue so check that out too.
If there are ribbon cables between boards, unplug them one at a time to see if that cures the problem, that way you can work out which board has the issue, and maybe fix it or leave it unplugged.....
Enzo's suggestion to put your finger on every ic to work out what is getting hot is an excellent place to start.
Replace the regulators and pwoer supply electrolytic capacitors. Measure the 48V, +17V & +17V rails. If any one is low, something is dragging it down and there is a faulty part.....

Good luck