c. Remove tube shield and defective tube
Replacement of RPM
from RPM check assembly.
Tubes (Takcal Unit.)
The RPM check assembly is provided with
a 12BH7, nine-pin base, twin-triode tube; an
Use only ruggedized tubes
OA2, seven-pin base, gas-filled voltage regulator
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
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
The deck gasket should be
replaced at each remov-
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.
Section IV. REASSEMBLY AND ALIGNMENT
c. Alignment. The only alignment neces-
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-
justment procedures for the potentiometer,
4-39. BH1766 Printed Circuit Board Assembly
check circuits of the tester.
(1) Connect and solder all compo-
dures for the egt indicator
check circuit are necessary
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
(3) Install rectifiers (2) and fuse
(13) in fuse and rectifier holders.
a. Reassembly. No reassembly of voltage
Observe polarity when in-
regulator is required.
stalling rectifiers. Arrow-
(1) Install voltage regulator (7) on
rectifier should point to-
ward positive (+) termi-
(9) and bolts (8).
nal. Rectifier holders are
connect wiring to rear of voltage regulator (7),
b. Installation. (Figure 4-6).
(1) Connect wiring to voltage regu-