# Spending a little time on a dead Behringer BX1200 before I recycle it



## buckaroobanzai (Feb 2, 2006)

I have had this BX1200 as a practice amp/acoustic amp/drum monitor for a few years. A while back it stopped outputting sound from all outputs ( speaker, headphones, line out) and puts out 120hz hum instead.

Having seen millions of pounds of electronics get crushed over the last few years, I am reluctant to toss out even a Behringer if I can fix it and pass it along to somebody starting out.

So far, thanks to threads on Google, I have replaced a shorted 7915 regulator and both amp chips. (LM3886's or whatever, I dont have the specs in front of me right now.)

I now have steady +/-15v rails and approx +/- 40v on the power pins of the main amp chips, which is supposed to be about right. Still no output and same hum.

There is a power cable that joins the power amp board to the jack PCB on the back of the amp. The jack pcb has all the input/output connections on it as well as some SMT resistors and such. I would have expected that this power cable would carry some sort of voltage, since it is two wires, one red, one black, and definitely looks "power cable-ish". There is no voltage on this cable, so I am wondering if that is a clue to the problem.

If anyone has taken a shot at fixing one of these, I'd like to hear about it. Thanks!


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## jb welder (Sep 14, 2010)

Schematic here (wait till it says "get manual" under the preview): http://elektrotanya.com/behringer_bx1200_ultrabass_rev_h_schematics.pdf/download.html

Hard to say if the reg. just went bad or a bad IC killed it.
The hum could be bad supply filtering (cap or cap solder connection), check the +/-15 and +/-40 rails for AC voltage. Some meters can't measure AC on DC properly, check a 9V battery with your meter set to AC volts, should read zero.


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## buckaroobanzai (Feb 2, 2006)

Thanks for the schematic, I will pull the amp back apart and do some more digging. Working on my circuit tracing skills can't hurt...


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## Church-Audio (Sep 27, 2014)

See if your getting dc on the output of the amp if you are its a bad op device. Or like has been mentioned a bad filter cap or bad solder joint. I would measure the output first no load for dc. See what you get if its in volts your op device is bad. If in mv doc then it's a filter or solder joint issue. These are all wave soldered so bad solder joints are suspect number one...I use chopsticks and whack the hell out of the pub board finds bad solder joints fast!


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## buckaroobanzai (Feb 2, 2006)

Well, I think I'm done with this amp. Power amp section tests ok, hum disppears when I unplug the ribbon cable going to the preamp/control board. That's the board with all the pots on it. Visual inspection of the board shows nothing. It's all surface mount stuff so there's not much I can do with it. I will recycle the chassis into a monitor speaker or something. Thanks to the folks who responded.


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