Lenovo ThinkCentre M57 Hardware Maintenance Manual - Page 11

v Always look carefully for possible hazards in your work area. Examples of these hazards are moist floors, nongrounded power extension cables, power surges, and missing safety grounds. v Do not touch live electrical circuits with the reflective surface of a plastic dental mirror. The surface is conductive; such touching can cause personal injury and machine damage. v Do not service the following parts with the power on when they are removed from their normal operating places in a machine: - Power supply units - Pumps - Blowers and fans - Motor generators and similar units. (This practice ensures correct grounding of the units.) v If an electrical accident occurs: - Use caution; do not become a victim yourself. - Switch off power. - Send another person to get medical aid. Safety inspection guide The intent of this inspection guide is to assist you in identifying potentially unsafe conditions on these products. Each machine, as it was designed and built, had required safety items installed to protect users and service personnel from injury. This guide addresses only those items. However, good judgment should be used to identify potential safety hazards due to attachment of features or options not covered by this inspection guide. If any unsafe conditions are present, you must determine how serious the apparent hazard could be and whether you can continue without first correcting the problem. Consider these conditions and the safety hazards they present: v Electrical hazards, especially primary power (primary voltage on the frame can cause serious or fatal electrical shock). v Explosive hazards, such as a damaged CRT face or bulging capacitor v Mechanical hazards, such as loose or missing hardware The guide consists of a series of steps presented in a checklist. Begin the checks with the power off, and the power cord disconnected. Checklist: 1. Check exterior covers for damage (loose, broken, or sharp edges). 2. Power-off the computer. Disconnect the power cord. 3. Check the power cord for: a. A third-wire ground connector in good condition. Use a meter to measure third-wire ground continuity for 0.1 ohm or less between the external ground pin and frame ground. b. The power cord should be the appropriate type as specified in the parts listings. c. Insulation must not be frayed or worn. 4. Remove the cover. Chapter 2. Safety information 5