WARNING When you are troubleshooting and doing repair work, TREAT ELECTRICITY WITH RESPECT. Working with electricity is hazardous, and you must take every precaution to avoid electrical shocks, burns, and electrocution. Regard all circuits as live until you have opened the switches or have made voltage tests and know that the circuit is dead. Lock and tag all switches in the OPEN position to keep other personnel from tampering with them and creating a safety hazardous condition. Remove protective devices, such as fuses, from their holders. REMEMBER, YOU WILL BE WORKING ON THAT CIRCUIT.
Controls and elements on appliances or equipment will most likely be your biggest problem. Check switches and controls with an ohmmeter for the making or breaking of contacts. If the switch is ON, the ohmmeter should read "0." The operation of a switch can be checked with a voltmeter. Check for voltage input and output.
New switches are usually inexpensive, so repairing an old one is not economical. The contacts may be reformed as a temporary measure to ensure a positive contact for completing the circuit. Lubricating the contacts and spring mechanics with a nonoxide grease reactivates the switch operation.
Repair of the bimetallic blade control switch is limited to an adjustment in the temperature setting of the control to agree with the temperature recorded in the appliance or equipment being tested. Temperature of equipment should be tested by a reliable temperature tester or a good thermometer.
Repair of the helix control is limited to adjusting the temperature setting of the control to agree with the temperature recorded in the appliance or equipment being tested. If the control cannot be adjusted, the complete control assembly must be replaced.
If a timer fails to operate, use the following procedures to locate the trouble:
Test the electrical circuit for a blown fuse.
Check for friction between the hands of the timer and timer crystal.
Check all wire connections.
To repair an inoperative electric timer, perform the following steps:
Replace the blown fuse with a fuse of the proper rating.
Replace the complete rotor if the rotor is inoperative.
Replace the complete coil assembly if the field coil is burned out.
Repair the timer switch assembly by cleaning contacts or reforming the contact arm to ensure positive contact. If the contact shows excessive wear, replace the switch assembly.
Adjust the hands of the timer if they are binding.
Check all connections at the back of the timer for positive contact to ensure a complete circuit.
Elements can be checked using a -voltmeter or ohmmeter. If a voltmeter is being used remove one wire from the element and check for voltage between the empty terminal and ground. A voltage reading indicates a good element, and no voltage indicates an open or defective element.
If an ohmmeter is used, first ensure that the power is disconnected. Remove both conductors to prevent a false reading. Connect the two leads of the ohmmeter to the two terminals of the element. A reading of zero indicates a good element. A reading of infinity symbol indicates an open element.
If you have ever had an encounter with an ungrounded electric drill while working in the rain, you have a feel for the importance of tool testing. You will also have gained a healthy respect for the person who tests tools at the battalion central tool room (CTR) or the Public Works Department (PWD) when he or she fmds and corrects the problem with portable electric power tools.
The tool tester shown in figure 7-16 is an example of a tool tester that personnel from CTR or PWD might use.Continue Reading