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Rattery Low Indicator
-4.65
IC6q11 is connected to 0 volts at
051
collector. The non-inverting input is
connected to the iunction of R15!VR152, which is approximately 0.5 volt
lositive with respect to
051
emitter. When the volt drop across Q51 falls to about 0.5
volt IC6/1 is at a potential below that of IC6/2 and IC4"12 goes to '1', lighting
LP8.
)ver Discharge Protection
1.66
The Battery Low indicator
I
ights when only a few minutes of battery Iife remain.
If this warning is disregarded the instrument will shut itself off to prevent battery
damage.
L67
Rl50 and D28 are connected across Battery A.
If
the voltage falls below about
5
vo! ts
033
will start to turn off. Th
is
will turn off
036
and render D30
'l1effective as the source of reference voltage for IC11a.
The voltage of the
+5
volt rail
ill fall and the instrument will cease to draw current.
)verload Protection
4.68
Battery B
is
protected by 035.
In the event of overload the potential across
R154
will turn 035 on, and so shunt the base current away from
052.
This
I
imi ts
_"he current available From the
-5
volt supply.
;TANDBY OFf RATION
4.69
With 153 at OPERATE the base of 050 is connected to ground via
R125,
and it
is
able to conduct.
With the switch at STANDBY 050 is cut off because Q30
__ is normally cut off by IC6b.
This disconnects the
~
vol t roil and removes the reference for
the -5 volt regulator.
Tbe internal frequency standard remains powered from a connection
:It
050 emitter.
LP6
anode is also supplied from this point, and since the
+5
volt supply
~'ail
is at 0 vol ts
is
able to
I
ight via 1
R3
to indicate the Standby condition.
oattery Economy Operation
4.70
Pressing the RESET push button while STANDBY is selected causes rapid discharge
of C83 via D25.
This results in the potential of IC6b/7 falling below that of
-IC6b/6, and IC6b/10 goes high, switching on 030 and therefore 050. This' restores the
supplies, and the instrument will operate normally until C83 recharges via R131 and triggers
IC6b back to its original condition. This takes about one
rr~inute.
The OVERFLOW/STANDBY
--indicator
I
ights when the instrument reverts to the Standby condition.
4-12
9916Vol.2
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