TM 55-4920-244-14
c. Remove tube shield and defective tube
from RPM check assembly.
Tubes (Takcal Unit.)
The RPM check assembly is provided with
CAUTION
a 12BH7, nine-pin base, twin-triode tube; an
Use only ruggedized tubes
OA2, seven-pin base, gas-filled voltage regulator
for replacement.
tube; and a 6202, seven-pin base, full wave rec-
tifier tube. The 12BH7 tube (6, fig. 4-9) is used
d. Install proper replacement tube and
as a resistance coupled amplifier. The OA2 tube
tube shield in RPM check assembly.
(4, fig. 4-9) is used to maintain power used by
the 12BH7 tube circuit at 150 volts. The 6202
e. Carefully lower deck assembly (4) on
tube (3, fig. 4-9) is used to transform ac power
flange box assembly (18).
to dc power.
a. Perform steps (1) through (3) of
NOTE
CAUTION
The deck gasket should be
replaced at each remov-
Knob (3, fig. 4-6) must be
al; however, if a new
removed before attempt-
deck gasket is not avail-
ing to raise deck assembly.
able, exercise care to pre-
serve the original deck
its edge and properly support.
gasket.
Section IV. REASSEMBLY AND ALIGNMENT
c. Alignment. The only alignment neces-
4-37. General.
sary is that the knob pointer be at 0 when the
This section contains instructions for au-
voltage regulator is against its counterclockwise
thorized reassembly and/or installation and ad-
stop.
justment procedures for the potentiometer,
resistance check, insulation check, and RPM
check circuits of the tester.
and Cable (Figure 4-6).
NOTE
a. Reassembly.
No
(1) Connect and solder all compo-
proce-
adjustment
dures for the egt indicator
nent leads removed in paragraph
(3).
check circuit are necessary
(2) Plug transformer (11, fig. 4-7)
The circuit will be proper-
into socket on printed circuit board (24) and
ly adjusted if the potenti-
align mounting studs with mating holes in
printed circuit board. Carefully work studs
ometer circuit is in ad-
through holes until printed circuit board is
justment. Refer to Table
4-1 for egt indicator check
flush with transformer housing. Install nuts.
(3) Install rectifiers (2) and fuse
circuit troubleshooting.
(13) in fuse and rectifier holders.
NOTE
a. Reassembly. No reassembly of voltage
Observe polarity when in-
regulator is required.
stalling rectifiers. Arrow-
b. Installation.
head of diode symbol on
(1) Install voltage regulator (7) on
rectifier should point to-
box assembly (18) and secure with lockwashers
ward positive (+) termi-
(9) and bolts (8).
nal. Rectifier holders are
(2) Using figure 4-15 as a guide,
polarized.
connect wiring to rear of voltage regulator (7),
4-6).
(1) Connect wiring to voltage regu-
(3) Install deck assembly (para. 4-
lator (7).
