Story

We use a number of the B205D PA/Monitor speaker as foldbacks in my local church. We are slowly moving away to using in-ear monitors to reduce the stage volume, but there are still times where the monitor speaker is useful. We have 3 fully working ones, and one that has one of the XLR inputs taped over and rattles when you move it.

Teardown

The unit is easy to disassemble, with a number of self-tapping screws holding it together. It became immediately obvious that the rattling was in fact the speaker magnet that had become detached from the diaphragm. This is not something that can be easily fixed, so instead a 5 inch speaker from amazon originally destined for a car audio system was sourced to replace it. Next, the taped up front input. Further disassembly revealed that an electrolytic capacitor had blown up. Fortunately the body of the capacitor was still inside the enclosure, so I could replace this was a part from my capacitor kit. The input still did not function, so I found the schematic that pointed me to suspect the quad op-amp configured as an instrumentation amplifier. An instrumentation amplifier consists of 2 op-amps buffering the input into a third, with a single resistor used to set the gain. This is ideal for the monitor speaker as it takes a differential signal from the XLR connector and amplifies it with a single volume control. I was going to replace the quad op-amp with an identical part (TL074) but decided to "upgrade" it with a OPA4134. This is over 10x the price, but it didn't break the bank. I'm not even sure that anyone will be able to tell the difference... Last issue was the rear input, which also was not working. Thankfully, from the schematic, there is only one op-amp between this input and the other inputs that were now all working fine. I replaced the faulty op-amp with a BA4580 dual op-amp and everything was as good as new.

Total Cost

• Speaker: £12.19
• Capacitor: £0.04
• Quad op-amp (OPA4134): £4.87
• Dual op-amp (BA4580): £0.50
• £17.60

Final Thoughts

I'm not sure I would've been able to fix it as quickly without the schematics. It is a shame that these were not available directly from Behringer, and I was fortunate that someone else had published. I have been told stories about when schematics used to be provided along with equipment. I can only assume that this practice stopped as companies were afraid that they would lose revenue through the repair of electronics, rather than just replacing them. I began the fix without the schematics, and as we will be phasing these out I don't see we'll be replacing them, but the repair process was still interesting, especially due to the simplicity of the design.