Casella CEL CEL-281 - Manual (Page 126)

The connector is keyed so that the plug can be inserted only the
correct way.
7. Carefully replace the upper circuit board.
Locate the three 3-pin connectors, and make sure the contact
strip comes inside the battery compartment.
8. Without replacing the front cover at this time, insert a fully
loaded battery holder into the battery compartment.
9. Either hold the battery pack in place by hand to ensure a good
electrical contact, or slip an elastic band round the instrument.
Figure 23: Replacing the microphone
Spacer
910039
Adjust This
Potentiometer
DO NOT
Adjust This
Potentiometer
Contact
Front Cover
Upper Board
Lower Board
Rear Cover
Strip
Controls Cover
Insert
Three x 3-pin
Connectors
Microphone
Socket
Technical Information
CEL-281 Operator's Handbook - Page 117