TM 1-1520-238-T-4 4–145 4–57. EXCESSIVE TORSIONAL VIBRATION AND N_R DROOP OCCURS DURING FLIGHT – 4–57 (ENGINE 1 N_P LAGS BEHIND ENGINE 2 N_P DURING RECOVERY MANEUVER) Tools: Nomenclature Part Number Tool Kit, Electrical SC518099CLA06 Repairer’s Multimeter, Digital AN/PSM-45 Personnel Required: 68F Aircraft Electrician One person to assist References: TM 1-1520-238-23 TM 1-1520-238-MTF TM 55-2840-248-23 Equipment Conditions: Ref Condition TM 1-1520-238-MTF Suspect engine identified TM 1-1520-238-23 N_R droop compensator potentiometer adjustment – completed Access provisions – LN1, LN3, LN4 – doors opened WARNING Turn off power before detaching or attaching wires and connectors. High current 28 VDC or 115 VAC is present. Failure to do so could result in death or serious injury. 1. Check for open between: P41–4 and P41–13, P41–4 and P41–15. Does open exist? YES Go to step 3. NO Go to step 2. 2. Detach P21. Check for short between: P41–4 and ground, P41–13 and ground, P41–15 and ground. Does short exist? YES (ABY) Repair shorted wire. Go to paragraph 4–12. (ABZ) Replace wire harness (TM 1-1520-238-23). NO Go to step 4. 3. Check for open between: P41–4 and P21–35, P41–13 and P21–33, P41–15 and P21–34. Does open exist? YES (ABY) Repair open wire. Go to paragraph 4–12. (ABZ) Replace wire harness (TM 1-1520-238-23). NO Go to step 6. 4. Check for short between: J21–33 and ground, J21–34 and ground, J21–35 and ground. Does short exist? YES Go to step 5. NO Refer to TM 55-2840-248-23 to troubleshoot engine 1 HMU, (ABY) ECU. (ABZ) DECU. 5. Detach P1121. Check for short between: P1121–4 and ground, P1121–5 and ground, P1121–6 and ground. Does short exist? YES Repair shorted wire. Go to paragraph 4–12. NO Replace collective potentiometer position transducer (TM 1-1520-238-23).