What was found
REPEATED, 4 CONSECUTIVE AFT AND 3 CONSECUTIVE REPAIRED UNITS, FAILURE OF EIS, ENGINE INSTRUMENT SYSTEM, DISPLAYS DURING SELF TEST FOUND AT ANNUAL/150 HOUR INSPECTIONS. FAILURES ARE A CODE 25, FAILURE OF RS232 RECEIVER, INTERNAL OR APU A OR B MONITOR TEST FAILURE, INTERNAL. RESOLUTION IS TO REPLACE THE UNIT. ROUTINELY RECEIVE REPLACEMENT UNITS WITH SAME CODE 25.