Capacitors and cathode ray tubes (CRTs)

TM 38-260

CAUTION

AT NO TIME SHALL EQUIPMENT BE DISCONNECTED BY CUTTING OR OTHERWISE

DAMAGING WIRES AND CABLES.

(1) All switches and circuit breakers of the electronic equipment will be opened, or set to the "OFF" position,

and the equipment will be completely disconnected from the power source.

CAUTION

ALWAYS CONSIDER

ELECTRONIC

EQUIPMENT

DELICATE

AND

HANDLE

CAREFULLY.

(2) Opening the equipment. Prior to opening the cabinet, measures should be taken to prevent damage to the

internal electronic components of the equipment by complying with the requirements listed in paragraph 4-24. c. The

electronic equipment should be opened so that the wiring and component parts may be reached for processing. The

ways of opening different electronic equipment varies almost as much as the locations of the component parts of the

equipment. There are various combinations of doors, panels, chassis covers, and sliding units. These must be

unfastened and opened or removed from the equipment. Detailed instructions for opening should be found in the

instruction manual accompanying the equipment.

(3) Capacitors and cathode ray tubes (CRTs)

(a) Discharge capacitors. After the electronic equipment is completely disconnected from power, all high-

voltage capacitors and CRTs should be discharged by qualified personnel. Equipment manufacturers sometimes place

warning signs on equipment near the terminals of high voltage capacitors. The terminals of many high-voltage

capacitors are automatically short-circuited when the equipment is turned off. Automatic shorting devices are intended

only to safeguard the incautious and should never be relied upon.

(b) Electrolytic capacitors. This type of capacitor tends to deform after extended periods of time

(approximately 2 to 10 years, depending on the electrolyte). The capacitors act as a short in the circuit when they deform

and risk damaging the electronic components of the equipment. The capacitors could be reformed by running the

equipment, but this risks shorting the equipment. A tag, conforming to UU-T-81 identified in MIL-STD-129, should be

attached to the power supply capacitor after discharging stating the following: "DO NOT POWER UP EQUIPMENT

UNTIL TESTING THIS CAPACITANCE WHEN EQUIPMENT HAS BEEN INACTIVE FOR MORE THAN 2 YEARS. "

(4) Grounding rod. A grounding rod is one method which may be used to discharge capacitors. The grounding

rod should be used as follows:

(a) Solidly fasten the ground clamp to a reliable ground on the equipment such as a clean, unpainted metal

part of the chassis or frame.

4-25