CHAPTER 3 MAINTENANCE - TM-11-6665-245-340017

TM 11-6665-245-34

CHAPTER 3

MAINTENANCE

Section I.

GENERAL

3-1 Maintenance Procedures

d. Testing Repaired Equipment. Once the

equipment fault has been located and corrected,

a. L o c a t i o n of Troubles. The location of

the equipment should be put through a series of

troubles begins with the gathering of symptoms.

tests to determine if it is ready to be returned to

Then, with knowledge of the equipment function-

service. The complete test for the radiacmeter is

ing, a determination can be made as to what sub -

contained in paragraphs 3-13 through 3-16. Per-

system is defective. From that point, more symp-

form all procedures contained in those

toms are taken, usually with the use of test equip-

paragraphs after repair of the equipment.

ment and further determination can be made until

e. Precautions. Certain precautions should be

the faulty component is located. This process is

observed while working on the radiacmeter. The

c a l l e d localization and isolation and is the

precautions concern possible injury from elec-

general troubleshooting procedure that should be

trical shock and damage to the photomultiplier

followed to locate troubles.

tube when it is exposed to light.

b. Gathering Symptoms. The skill of gathering

(1) High voltage of approximately 950

symptoms is learned from experience on the

volts is used to energize the photomultiplier tube

equipment. Without this skill, it is best to follow a

contained in the probe handle. The high voltage is

set procedure based on the following:

g e n e r a t e d on the radiacmeter printed circuit

(1) Make a quick. visual check of the

board and transmitted through the coil cord to the

equipment to try and spot obvious troubles quick-

probe handle. Be sure to locate the high voltage

ly rather than as a result of a lengthy testing or

points on the printed circuit board (PCB) prior to

troubleshooting procedure. Use the quick visual

energizing the equipment when troubleshooting.

check at each stage of the disassembly of the

(2) The photomultiplier (PM) tube must be

equipment, not just at the start of the procedure.

protected from bright light when the equipment is

(2) Do the easy things first. Check for:

off. When the equipment is on, no unintended

blown or missing fuses; bad power cables and

light should be allowed to touch it. Under some

connectors; make the checks which are simple

conditions, light will either damage the tube or

and fast to do.

reduce its operating life.

(3) Perform an operating procedure to

f. Measuring the High Voltage. The power

q u i c k l y check all controls, switches, and in-

supply which produces the -950 used for the

dicators. In the case of the radiacmeter, the

photomultiplier tube circuit has a very high inter-

operational test (para. 3-5) should provide quick

nal impedance. This presents a problem when try-

symptoms of trouble. If it doesn't, perform all the

ing to make voltage measurements using conven-

tests in paragraphs 3-12 through 3-14. If no symp-

tional meters. This is because the amount of cur-

toms appear, the equipment does not contain any

rent drawn by a conventional meter will reduce

faults.

the voltage being measured. In order to get an ac-

c. Repair of Equipment. Repair of the equip-

curate reading, a meter that draws no current

ment in most cases will `probably be the exchang-

(electrostatic voltmeter) or very little current (high

ing of defective parts, printed wiring boards, or

input impedance vacuum tube voltmeter) should

assemblies with new ones. Procedures for replac-

be used. When those types of meters are not

ing the radiacmeter assemblies are contained in

available, use a conventional meter, but realize

paragraphs 3-6 through 3-12. The extent of further

that the voltage value read has been reduced,

repair d e p e n d s u p o n t h e e q u i p m e n t ' s

possibly up to several hundred volts, from the ac-

m a i n t e n a n c e concept as presented in the

tual value.

Maintenance Allocation Chart (TM 11-6665-245-12)

and

the repair parts available (TM

3-2. Maintenance Data

11-6665-245-23P). Certain parts can be replaced

Maintenance data in this manual for the

without affecting the equipment's calibration,

radiacmeter includes: schematic and wiring draw-

while adjustments must be made when other

ings, (Figures 3-1, FO-1, and FO-2); parts location

parts are replaced. After a repair is made, and

illustrations (Figures, 3-2 and 3-4 through 3-8); and

prior to testing, check in paragraphs 3-15 and 3-16

voltage waveform data (Figures 3-3 and 3-8).

to find out if adjustments are necessary.

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