A couple of years ago I purchased a used Hohner B2A Headless Bass. I love playing it! It’s light. It’s unique looking. It wasn’t too expensive. And it has Steinberger hardware. It also has active electronics.
At some point during my playing it the active electronics failed. That is to say that when the bass was plugged into a guitar cable and the switch was turned on the LED did not light nor did the extra volume kick in. I replaced the battery and made sure the contacts were clean but still no dice. The bass still operated fine with the active electronics switch turned off, however, the fact that it wasn’t fully functional bothered me.
I decided I would try to diagnose and repair the problem. I didn’t think the problem would go too deep unless there was some type of component failure in the active electronics themselves. Fortunately I was correct. The first thing I did was to ensure I had details on the wiring of the bass. Through some searching on the Internet I was able to come up with the following diagrams. Each was discovered through forums and I never found the original poster but whoever you are; thank you!
Starting at the beginning of the electronics chain I checked the power connection to the battery compartment. There are two metal contacts inside the battery compartment and I suspected they may not be making contact with the battery properly. As it turned out I was correct in this assumption. To test my theory I connected a pair of alligator connectors (the greatest electronics debugging tool) to the leads connected to the battery compartment and tested them with a multimeter. Bingo! No juice was getting through to the electronics. This, of course, would definitely have an effect on the rest of the circuitry.
Once I determined that the power wasn’t getting out to the electronics from the battery compartment I tested the theory by wiring a battery directly to the power leads using alligator clips.
This setup made the active electronics work. Remember that if you want to test the electronics you must have a 1/4″ guitar plug inserted into the bass otherwise the electronics will never turn on.
At this point I used some contact cleaner to clean off the battery connection points inside the compartment and I gently bent the metal contacts outward so they would be sure to make contact with the battery terminals. This worked out perfectly and the bass’ electronics were active once more.
Having the bass on the bench already I decided to have a look inside the main compartment to ensure everything was ok. Older gear is susceptible to solder joints coming loose over time and I was experiencing a glitch with the electronics volume control.
Close inspection revealed that the solder joint on one wire leading to the potentiometer and come loose. That would explain the intermittent problem.
A quick soldering touch up and the wire held firmly in place. Remember when soldering to clear away any wires (gently) to ensure the shielding does not get melted by the shaft of the soldering iron.
I cleaned up the main compartment (it had dust in it) ,sealed up the electronics compartments, gave the bass a polish and presto – new life for an old bass. I really love this instrument – it’s so much fun to play!
UPDATED: Hohner Parts List