The 2in1-PCB must be connected using one of the mini ribbon cables. The 6-pin connector must be located towards the PCB. Pin 1 is on the bottom left (component side up). On the other end of the cable there are 1-pin female connectors. They must be connected to the following pins on the (male) 40-pin-conenctor in the middle of the main ribbon cable.
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Connect the 6-pin dupont wire to the 2in1 module in the case. Numbering is from left to right and pin 1 is the brown wire:
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Next connect the DIN socket (MIDI) to the 2in1-PCB. The connector on the PCB is the 2-pin one located in the upper right corner of the PCB.