Check Mode; Power Supply - Racal Instruments 9916 Workshop Manual

4.50 When the RESET button is pressed a 'QI is appl ied at IC12b/l Q via the reset
circuitry. This puts IC12b into the preset state. IC12b/9 goes to '1', which is
applied to IC19q!2. Since IC19q!1 is at '1' when BURST is selected IC19a puts a 'Q' onto
lIC1/4, blanking the display. IC12b/8 goes to 'Q', holding IC12a in the cleared state.
When the RESET button is released IC12b is freed from the preset condition, and can respond
to clocking signals.
4.51 The incoming signal to be measured is applied to IC12b/ll, clockinglC12b/9 to
IQ' and IC12b/8 to 11'. The 'Q' is appl ied to IC19q!2, removing the display
blanking. It is also applied to IC12q!2 via
C68.
When the 'l' at IC12b/8 releases IC12a
from the cleared state it can be clocked by the lQ kHz signal at IC12q!3, but since IC12q!2
is at
'0'
no change of state occurs.
A.s
C68 charges, however, IC12q!2 reverts to the '1'
state, and after a delay of 40 ms IC12q! 6 is clocked to '0'. This delay provides settl ing time
for the input ampl ifiers.
4.52 The step at IC12q! 6, differentiated by C69 and R94/R96, is fed to IC17c/9
giving a positive going pulse at IC17b/5 and IC13q!1. IC4/13 is taken to 'Q' by
IC17b for the pulse duration, initiating a new measurement cycle on the 11' to IQ' transition
and then returning to the Hold condition so that the display will be held at the end of the
gate period. IC13q!3 goes to '0' and causes IC2b to generate a stores update pulse at
IC4/4. The circuit will remain in this condition until the RESET button is pressed again.
CHECK MODE
4.53
With the FUNCT 10 N switch set to CHEC K lC8b/9 is at '0', IC9c/9 and 10 are
at '1' and IC24d/13 is at '1'. If
'A'
Channel is also selected IC10q!1 is at '0',
putting IC24cV12 to '1'. \
C24q!
11 therefore goes to '0', and this level, appl ied to l1C1/3
gives an 'all eights' display for segment checking.
4.54
With CHECK,and 'B' Channel selected IC8b is inhibited by the '0' at pin 9,
IC9a is inhibited by the '0' at pins 1 and 2, IC9b is inhibited
by
the '0' at
pin 5. IC9c is enabled by a '1' on pins 9 and 10, and passes the 1 MHz from IC4/6 to the
-:ounter circuits.
POWER SUPPLY
Line Power
4.55 With the LINE POWER/CHARGE/BATTERY POWER switch (52) at LINE POWER
the supply is fed via a 3-pin plug/filter connedtor on the rear panel, fuse FS50,
the POWER swi tch and 552 to the primaries of T50. The transformer tapp ings and 552 must
be set to suit the local supply voltage as shown in Fig. 5.1 -
4.56 The output of secondary 'A' is rectified in the potted bridge rectifier D5Q and
smoothed by C101 to provide a supply for the
+5
vol t stabil iser. The output of
secondary 'B' is rectified in the diode bridge D31 to D34 and smoothed by Cl02 to provide
the -5 volt stabiliser supply. The -5 volt rail is protected by FS1, which must be of the
quick action type.
4-8
9916Vol.2