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Jul 19

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Repairing a Behringer BCF2000

BCF2000 is a good, cheap MIDI controller manufactured by Behringer. It can be used (and in fact is widely used) in live music industry, either by light technicians, DJs or musicians.

bcf2000

bcf2000_problems

So one day I got a request to do lighting in a live show and needed my BCF2000 that was idle for a couple of months. Surprisingly, I came across a strange issue: some buttons were triggering other ones, causing multiple MIDI commands to be sent to the computer when I pushed a single button.

After tearing it down, I searched for bad capacitors but with no luck. Everything inside looked cool. The next step was to search for schematics online. Again, no luck for me. There are no electronic schematics available for these desks.

With multimeter, oscilloscope and a solder iron, let’s do some reverse engineering on the unit!

Reverse Engineering

At this stage, my only choice was to grab my old multimeter and try to reverse engineer the schematics of the buttons interface. The silkscreen on the PCB was unexpectedly  verbose and helped through the process.

There are few ways to interface a micro-controller with several buttons, being the keyboard matrix method one of the most used. This was the case of BCF2000 where buttons are scanned sequentially in columns and several rows are read in parallel as you can see in the following picture.

keymatrix

The transistors used to scan through the columns are also used to drive the LEDs on the buttons and the LCD screen on the top board.

Transistors check

The first thing to check was the transistor activation signals. They must be time multiplexed, so that only one transistor is activated at a time. With the oscilloscope, it was verified that every transistor was being activated and in a correct time.

20130719_120657

Then I found that the buttons (both in the main board and in the top one) with the problem all shared the same transistor… Hmmm… Checked the collector of that transistor and the others and in fact the signal was very different. Although it was being activated on the correct time, the voltage remained higher that the other transistors when in OFF state. The obvious test was to change the transistor (BC327-25) with a new one… The problem persisted!

The next move was to disconnect the top board from the main one while watching the signal on the collector of that transistor. The OFF level dropped to “normal” values as soon as the board is disconnected. Testing the “faulty buttons” of the main board, now the problem has disappeared!!

Ok, so definitely the problem was somewhere in the top board.

Inspecting the top board

Down to the top board, all the electronics on the main board (flip-flops, transistors, capacitors, etc) were out of my suspections.

So this top board consists in a bunch of pushbuttons, indication LEDs, dual LED displays, rotary encoders, parallel in – serial out ICs and some discrete components, including the diodes of the buttons. The 2 ICs (74HC165D) were being used to catch the rotary encoders signals and send them in serial to the main board.

The first thing was to test continuity between the output of a faulty button and the output of a (wrongly) triggered button. No connection between the two.

I knew that diodes play a very important role in the correct identification of pressed buttons. Therefore, I tested every single diode for forward and backward continuity. Bad luck, the diodes were all ok :(

At this point, I was starting to feel frustrated by having such a simple board in front of me and not being able to track the origin of the problem.

With absolutely no hope, I started to inspect the 7 segments LED displays. You can do that by selecting the continuity check mode in the multimeter and activating a segment at a time. The polarity you test will make it possible to track the common side of the LEDs (anode or cathode) and the combinations will lead you the common pin numbers. It turns out that the BCF2000 includes two dual-digit (with dot point) Common-Anode (pins 5 and 10) multiplex drive – 10 pins total (see picture below).

ledDisplay

Testing each segment individually revealed a problem in the left display: two segments were dead. As these were connected to the same matrix of the buttons (in fact one of the common pins shared the same transistor of the faulty column), I carefully removed the left display and ran the tests with the top board connected.

Problem Solved!

Then the second part came: find a display that can replace the faulty one as the references printed in the display lead to fake Chinese sites.

If you come across this problem, I’ve done all the hard work for you: Everlight ELD-426USOWA meets the strange pinout and dimensions of the display. I ordered some from Mouser and am currently waiting for them. (I’ll update as soon as I test it)

The BCF2000 is now up and running (for now, with just the last 2 digits)… :D

20130717_183629

Update 28/07/2013

I received the LED Display from Mouser and unfortunately the pins are not as long as the original one. The result is on the photos below. If you look from the top, you won’t notice a difference… At least, IT’S READY TO HIT THE ROAD!

20130728_212413

20130728_230759

About the author

Ricardo Dias

Ricardo Dias was born in Entroncamento, Portugal and is studying Electronic and Telecommunications Engineering at University of Aveiro. He is a researcher in robotics and is currently the Team Leader of CAMBADA@MSL team. As a hobby, he is also a freelancer Stage Lighting Designer.

Permanent link to this article: http://ricardo-dias.com/2013/07/19/repairing-a-behringer-bcf2000/

11 comments

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  1. Danke

    Thank you for taking the time to post this. Very straight forward and simple to understand. Is the bcf2000 a piece of gear you trust for live shows? I am looking to purchase one for a home studio but never considered using it for a live show as it is in the “pro-sumer” market.

    1. Ricardo Dias

      Hey Danke,

      Thank you very much for your feedback.
      I definitely trust the BCF2000 for live shows! Considering its low price, is probably the best quality/price option.
      Of course, it has its issues. It should have touch faders to avoid forcing the motors, but you can’t find anything like it for the price.

      Best regards,
      Ricardo Dias

  2. J M SOREN

    MY BCF WAS WORKING FINE UNTIL ONE DAY I FOUND THAT IT WAS NOT STARTING. THEN I SMELLED SOME BURNING INSIDE. ALTHOUGH THE HOUSE WHERE I LIVE IS HAVING MCBs ( MINIATURE CIRCUIT BREAKERS, I THINK THAT BECAUSE OF THE MOISTURE INSIDE THE DEVICE HAS GONE BAD.
    PLS GUIDE.

  3. Cameron Duffy

    Hi Ricardo,
    first thanks for taking the time to post your results. I really appreciate it.
    I have a question… I broke both of my BCF2000 in a studio meltdown. The USB interface boards got broken on the socket and they don’t startup – no led light up.

    I would like to replace the usb interface board but where would I get them?

    Ive been looking for 2nd hand/broken bcf2000 but so far no luck.
    Alternatively I could swap the USB controller out of a BCR 2000 but im fairly ignorant of electronics.
    Have you tried swapping bits between BCR2000 and BCF2000?
    Its a lot cheaper to buy 2nd hand bcr2000.

    Your advice would be much appreciated
    Cam

    1. Ricardo Dias

      Hello Cameron,

      Thanks for your feedback :)

      This was my only repair job on a BCF2000, I don’t have any experience in using spare BCR parts in the BCF. Although the top part between the two models look the same, I suspect that the microcontroller board is different, because they have different inputs. In the front panel of the BCF, you have 8 faders (analog) and in the BCR you have 24 rotary encoders (digital) plus all the LEDs.

      Internally, the controls are linked in a matrix and the controller is continuously scanning all the controls sequentially (that’s called multiplexing), and in the BCR you have more controls to scan, so I think they are not compatible.

      I will contact you by e-mail to try to help you further, because I need additional info :)

      Best regards,
      Ricardo Dias

  4. Tomsoft

    I think perhaps you could have used a “wirewrap” IC-socket with long legs as a standoff to resolve the height difference using this part. For example:
    http://nl.mouser.com/ProductDetail/Aries-Electronics/06-1518-10/
    http://nl.mouser.com/ProductDetail/Aries-Electronics/8-3508-30/

    1. Ricardo Dias

      Hey Tomsoft!

      Thanks for the tip! That’s such an idea…
      Thanks for sharing with everyone!

      Best regards,
      Ricardo Dias

  5. dennis

    hi ricardo,
    i bought a broken bcf 2000 off ebay, and it was completely dead on arrival but reading your artical decided to look into it, first checks showed that the power supply was fine, delving further there was no supply on the main control board it turned out to be L1 was not soldered on one end, now i have a perfectly operating bcf2000
    thanks for sharing your work
    thanks
    dennis

    1. Ricardo Dias

      Hey Dennis,

      Nice to hear it’s working now! :)

      Best regards,
      Ricardo Dias

  6. Justin

    Awesome write-up, Ricardo. Just a shot in the dark- any idea where to source the PSU for the BCF2000? I successfully replaced the bad capacitors and then (idiotically) forgot to isolate the PSU when I tested it (it was laying on the metal frame of the unit), and it shorted out.

    1. Ricardo Dias

      Hey Justin,

      OUCH! :P No, I can’t help you, sorry :(
      If you remember or manage to get the output voltage(s) of the PSU, you might be able to replace it by an internal circuit of a consumer AC-DC transformer.

      Best regards,
      Ricardo Dias

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