HP 4001 Organizational, Ds, Gs, And Depot Maintenance Manual Download Page 28

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TM 11-6625-1514-15

Section V

Paragraphs 5-9 to 5-16

c. Rotate mechanical zero-adjustment screw clock-

wise until meter pointer is to the left of zero and mov-

ing upscale toward zero.

d. Continue to rotate adjustment screw clockwise;

stop when pointer is exactly on zero. If pointer over-

shoots zero, repeat steps c and d .

e. When pointer is exactly on zero, rotate adjust-

ment screw approximately 15 degrees counterclock-
wise.

This is enough to free the zero adjustment

screw from the meter suspension. If pointer moves

during this step, because the adjustment screw is
turned too far counterclockwise, repeat the procedure
of steps c through d.

5-9. CABINET REMOVAL.

a. Remove the two cabinet retaining screws at the

rear of the instrument.

b. Push the instrument chassis forward out of the

cabinet. The bezel ring remains attached to the front
panel.

c. When replacing cabinet, pull power cable through

opening at rear of cabinet. Be sure power cable is

not caught between chassis and cabinet. Replace re-

taining screws.

5-10. TUBE REPLACEMENT.

Do not remove tubes from the voltmeter when
power is applied.

To do so may damage the

voltmeter.

5-11. In many cases instrument malfunction can be

corrected by replacing a weak or defective tube. Check
tubes by substitution while following the voltmeter

performance check procedure in paragraph 5-22. Re-
sults obtained through the use of a “tube checker” can
be misleading.

Before removing the tubes from the

instrument, mark the original tubes so they can be
returned to the same socket if they are not defective.
Replace only those tubes proven to be defective.

5-12. Figure 5-2 lists each tube in the voltmeter with
its function and the check or adjustment required if

the tube is replaced.

5-13. REPLACEMENT OF SPECIAL PARTS.

5-14. PRECISION RESISTORS AND INDUCTORS. Sev-
eral parts used in the voltmeter have closer tolerances

than those used in most test equipment. Resistors
R104, R105, R108, and R111 through R116 are pre-
cision components. If these resistors require replace-

ment, use the same value and type as the original, as
shown in the parts breakdown.

If different values

are used or component positions are moved, the cali-
bration of the voltmeter may be inaccurate or the fre-
quency response may be altered. The inductance of

L10 and L11 affects the frequency response of the

voltmeter. Do not alter the shape or position of these
coils. Install replacement components in the same
positions the original components occupied, as nearly
as possible.

5-15. DIODE RECTIFIERS. Special high-performance
silicon diodes selected by the Hewlett-Packard Co.

are used for CR1 and CR2. When replacing the sili-
con diodes, be careful in soldering; heat can damage
them.

Place a heat sink (such as a long-nose pliers)

on each diode lead close to the diode body to conduct
the heat away.

If CR1 and CR2 are replaced, the

voltmeter calibration and frequency response must
be checked as described in paragraph 5-22.

5-16. RANGE SWITCH. Because of the critical con-
struction and wiring of switch S1, it is not practical

to attempt a major repair on the switch. When mech-
anical failure occurs in switch S1, replace the complete

CIRCUIT

TYPE

FUNCTION

CHECK OR