Heathkit IT -3120 User Manual

Page 32
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CIRCUIT DESCRIPTI I ON I
Refer to the Schematic Diagram (fold-out from Page 41)
while you read this "Circuit Description."
General Consideration
All of the following circuit explanations refer only to NPN
transistors or IN channel F ET's. The descriptions ali so apply
equally to PNP transistors and P channel FET's except that
the polarity of the meter and both batteries (B 1 and B2)
must
be reversed.
Diode
D1 1 protects the meter by limiting the voltage across it
to 0.6 volts. Capacitors C1 and C2 prevent oscillations from
occurring in the device being tested. Resistors R5 and R6
limit the current to protect controls R 11 and R 12 in case a
short circuit occurs. For simplicity, the above components
are
110t shown in the following partial schematics.
All switches are shown on the Schematic in the released
(out) position even though th is configuration does not
represent a particular test. This enables you to easily trace a
particular test
circuit by pressing (mentally) only the switch
related
to that test.
BATTERY TEST
Each battery is tested separately. The NPN position of the
NPN-PNP switch connects battery 82 into the battery
0
RX~
TESTED
1 A
100 m A
10mA
l
rn A
~ R8
i
R 1
~ R 2
~ RJ
~ R 4
., 10 K Q
15Q
1 5
I)
~ lS I)
~ 166 I)
)
"1
+ -
+
82
1 5V
BETA==
testing circuit. The PNP position of the NPN-PN IP switch
connects battery 81 into the 'battery testing circuit. A load,
simulating operating conditions, is connected across
each battery while the battery voltage is being measured.
This assures that the battery is capable of supplying
adequate current and voltage for the tests.
62
R2
1. Sv
1.SI)
1+
I
BAT TEST
Figure 5
When the Bat Test switch is pressed, resistor R2 is placed
across
the battery terminals to load the battery. See Figure
5.
The meter, now functioning as a voltmeter, measures the
battery voltage. If the battery is serviceable (0.9 volt or
more), the meter pointer will fall within the Bat OK mark
on the meter.
SET8 E TA·c,a
R 11
IS K I)
B 1
®
1. 5v
//~
82
I R l
Figure 6

Heathkit IT -3120 Specifications

General

Brand	Heathkit
Model	IT -3120
Category	Test Equipment
Language	English