ABSTRACT
Safety considerations Before we outline the basic steps for fault finding on some simple electronic circuits, it is vitally important that you are aware of the potential hazards associated with equipment which uses high voltages or is operated from the a.c. mains supply. Whereas many electronic circuits operate from low voltage supplies and can thus be handled quite safely, the high a.c. voltages present in mains operated equipment represent a potentially lethal shock hazard. The following general rules should always be followed when handling such equipment:
1. Switch off the mains supply and remove the mains power connector whenever any of the following tasks are being performed: (a) Dismantling the equipment. (b) Inspecting fuses. (c) Disconnecting or connecting internal modules. (d) Desoldering or soldering components. (e) Carrying out continuity tests on switches,
transformer windings, bridge rectifiers, etc. 2 When measuring a.c. and d.c. voltages present
within the power unit take the following precautions: (a) Avoid direct contact with incoming mains wiring. (b) Check that the equipment is connected to an effective earth. (c) Use insulated test prods. (d) Select appropriate meter ranges before attempting to take any measurements. (e) If in any doubt about what you are doing, switch off at the mains, disconnect the mains connector and think.
