We recently had the pleasure of repairing a Hammond New B3 Organ. This is the model right before the B3 Mk2 line. The organ and the Leslie 771 that the organ was connected too, was having issues. The audio outputs for the top two manuals on the organ were distorting through the Leslie and through the headphones port. What was interesting was that the bass pedals were not distorting through the headphones but were distorting through the Leslie. The first course of action to take, is to inspect all connections and make sure the 11 pin Leslie cables are properly seated. Next, we checked the incoming power and power connections. It looked like the customer did not have the organ on a sufficient power protection device. It was plugged directly into a wall outlet. Organs may have a rugged exterior, but their circuitry can often times be effected by the instability of power from the grid. That’s why we often recommend some sort of power conditioner/cleaner with digital control.

After inspecting all outside connections, we moved to the organ. Normally, we would first look at the Leslie in this situation, but we plugged the organ into another 771 Leslie that the customer had and it was still distorting. Also, the headphone port was distorting, so we decided to look at the MXH mixer and power board of the organ. Once inside the organ we checked all of the power rails and made sure they were within spec. Next, we connected our oscilloscope to the audio outputs of the MXH board. I do have to pause for a moment to write a disclaimer. Organs should not be repaired by amateurs. They can cause serious injury or death even unplugged. The amount of power stored in an organ through its capacitors can hurt you. That being said, we took all precautions when making these measurements and connections. Especially when using equipment like an oscilloscope that it also plugged into the grid. This instrument can easily be destroyed if proper connections are not made. By looking at the audio outputs, we could see distortion in the wave forms. Next, course of action was to run a sine wave signal into the audio input of the organ. By generating our own tone signal we can determine if the distortion is happening before or after the MXH board. The sine wave was clean on the output. This led us to the EFH D/A converter board.

The EFH D/A converter board, takes the electronic data from the CPU and converts it to analog waveforms. The waveforms were confirmed to be distorting on the EFH board. We replaced this board and that fixed the distortion of the waveforms in the EFH board and MXH board. This was also verified by listening through the headphones as well. The headphones were now as clean as a whistle. The only problem was we were still getting a slight distorted sound from the Leslie. Since the customer had two 771 Leslies, we plugged it into the other Leslie. There was no distortion on the second 771 Leslie. We decided to swap the Horn Power Amp and Bass Power Amp from the good Leslie to the bad Leslie. The sound was no longer distorted in the bad Leslie. The issue was the Darlington Transistor Pair on the Horn Power Amp. Since we were replacing the transistors on the Horn Power Amp, we also replaced the transistors on the Bass Power Amp as well. This is generally an inexpensive repair. Now the customer has a clean sounding organ and Leslie.

Sometimes organs can be tough to troubleshoot. But, by slowly eliminating different areas of question, organs can be repaired and brought back to working order. If you have any question about this job or any other jobs that we post, just fill out the form below.

Hammond B3 Organ Repair

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