TM 55-4920-244-14
c. Repair. No repair is required except to
(2) Identify and tag wiring. Unsol-
straighten bent pins.
der and remove wiring from toggle switch (98).
(3) Unscrew and remove seal nut
(99) from toggle switch. Remove toggle switch
from bottom of deck (128).
The RPM check assembly provides a pul-
b. Disassembly. No disassembly is re-
sating dc output independent of voltage varia-
quired.
tions in tachometer output, but proportional to
c. Cleaning.
frequency of tachometer output. The RPM check
(1) Clean switch with a soft brush.
assembly consists of a resistance-capacitance
(2) Use a cloth moistened in dry
coupled, two-stage, low-frequency amplifier used
cleaning solvent (item 1, table 1-1 ) to remove
to drive a sensitive relay at the engine tachome-
foreign matter.
ter generator frequency. As the tachometer gen-
d. Inspection and Testing.
erator shaft rotates, the relay contacts open
(1) Operate toggle switch several
and close, providing pulsating dc to a gal-
times. Toggle action should be positive with an
vanometer (GALVO-2) proportional to the en-
audible click as toggle switch operates.
gine tachometer generator frequency. As the fre-
(2) Make sure terminals and attach-
quency increases, the average dc component of
ing rivets are secure and will not turn or move.
the pulsating dc increases. The potentiometer
(3) Inspect switch terminals for cor-
connected to the RPM knob provides an adjust-
rosion.
able dc voltage to a galvanometers (GALVO-2)
(4) Using an ohmmeter capable of
used to balance the output signal from the RPM
accurately reading values of 1 ohm, check switch
check assembly. When zero indication is obtained
contacts for a closed circuit value of less than 1
on GALVO-2, percent RPM can be read on the
ohm and an open circuit value of at least 100
% scale.
megohms.
a. Removal.
(5) Inspect shank of toggle switch
(1) Remove deck assembly (para.4-
and attaching hardware for damaged threads.
32).
e. Repair. Replace toggle switch if any of
(2) Remove galvanometers (69, fig.
the conditions described in d above exist.
4-8) (para.
(3) On RPM check assembly (54,
4-26. Connectors. (Figure 4-8)
solder terminals and make sure attached wiring
NOTE
is coded to correspond with terminal designa-
Except for location of the
tions. Identify and tag any unmarked wiring.
connectors in the deck
(4) Unsolder all connecting wiring
and the number of solder
from RPM check assembly.
terminals, removal proce-
(5) Loosen setscrews and remove
dures are identical.
knobs from potentiometer (61) and selector
switch (12, fig. 4-9). Remove seal nut from se-
a. Removal.
lector switch.
(1) Remove deck assembly (para. 4-
(6) Remove screws (57, fig. 4-8)
32).
and lockwashers (59 which secure RPM check
(2) Identify and tag wiring. Unsol-
assembly (54) to deck (128). Remove RPM
der and remove wires from connector (78).
check assembly.
(3) Remove screws and lockwashers
that secure mount (9) (if applicable) and con-
(1) Unlatch clamp (19) and remove
nector to deck. Remove mount and connector.
relay (1) by unplugging from socket.
(2) Remove tube shields and tubes
NOTE
Remove gasket only if
NOTE
damaged.
Normally,
disassembly
(4) Remove connectors (88, 100, and
beyond this point is not
110) as outlined in (2) and (3) above.
accomplished except on an
b. Disassembly. No disassembly is re-
quired.
as required basis. Com-
4-23
