As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE SYS TEST PANEL ROTARY SWITCH STARTED WORKING INTERMITTENTLY, ESPECIALLY UPON PRESSING THE KNOB FOR TEST. RECEIVED A REPLACEMENT PANEL ASSY UNDER WARRANTY AND THAT UNIT WOULD NOT TEST PROPERLY UNLESS THE KNOB WAS WIGGLED A CERTAIN WAY WHILE DEPRESSED. THE THIRD UNIT RECEIVED WAS IN A CONDITION IN WHICH THE KNOB WOULD NOT PHYSICALLY PRESS DOWN. THE FOURTH UNIT RECEIVED WORKED OK. THE MFG TOLD US NOT TO RETURN THE NEW DEFECTIVE UNITS. THE ROTARY SWITCH ON THE PANEL, AND THE SN THAT FAILED ARE DC0838, DC0826, DC0910.