Table 5-1. Probe resistance checks

TM 11-6625-524-14-4

a . D i o d e C a r t r i d g e : D i o d e failure results from excessive Rr, AC or DC in-

p u t s . To test, remove the exposed setscrew on the side of the probe housing,

g e n t l y slide the cartridge out of the housing (see figure 5-2). Two (2) small

spring contacts will be seen on one (1) end of the cartridge, Care should be ex-

ercised, not to damage these contacts,. By placing the DC multimeter, set to ohms,

a c r o s s the contacts, a forward-reverse resistance ratio of approximately 800 times

should be noted with approximately 5K in the forward direction. Any other reading

w o u l d indicate a faulty cartridge. If faulty, replace.

T o replace the diode cartridge, first remove the grounding spring from the probe

housing. The spring may be reused only if clean and undamaged. During manufacture,

a thin protective film of white vaseline was applied to all silver-plated surfaces

t o retard oxidation, Care should be exercised to avoid removal of this film. If

t h e film has been inadvertently removed or if the contacts inside the probe hous-

ing have been cleaned, a thin film of white vaseline may be applied to the surface.

T h e cartridge should be carefully inserted into the housing, making certain the

s l o t in the side of the cartridge is aligned with the locking screw hole in the

side of the probe housing. The locking screw may now be inserted and tightened,

t a k i n g care that it properly engages the cartridge slot.

F i n a l l y , the grounding spring is inserted (note the correct position as shown in

f i g u r e 5-2). Positioning the spring may be facilitated by gently pushing the cart-

r i d g e all the way into the housing several times. W h e n the spring is in its correct

p o s i t i o n , the fingers will be flush with the edge of the probe housing. With a

l i t t l e thumb pressure, the cartridge should slide smoothly back and forth against

the spring-loaded socket assembly inside the probe housing. If it binds and does

n o t fully return after being depressed, the grounding spring fingers may be curved

excessively outward. The spring should be removed and the fingers flattened very

slightly by pinching them between the smooth area of a pair of long-nosed pliers.

Probe: To test, detach from the voltmeter and remove the diode cartridge.

With the DC multimeter set to ohms, perform the following resistance checks and

compare to the values as shown in Table 5-1.

Table 5-1. Probe resistance checks

Location

Resistance

10K ±5%

Plug Pin A to Pin B

l00K ±5%

Plug Pin A to Pin C

500K ±5%

Plug Pin A to Pin D

Plug Pin J to Blue Dot

10K ±5%

T e r m i n a l in Probe Housing

Plug Pin H to Non-Blue Dot

10K ±5%

Terminal in Probe Housing

Infinity

Plug Pin J to Pin H

Plug Pins A, J and H to

Infinity

Probe Housing Shell

Plug Pins E, F and K to

Probe Housing Shell

Less than 1

Any discrepancies in the above probe resistance measurements indicates a faulty

probe. The probe should be replaced.

6 U.S.

GOVERNMENT

PRINTING

OFFICE

1984-707-002

5-6