Tektronix 213 DMM Instruction Manual page 32

Theory of Operation-213 Service
acter segments. This negative unblanking signal is establish-
ed by the overrange detector, 0204; overrange latch U250A
and B; and the transistor switch, 0256. These are in turn
controlled by the overrange circuitry in the Buffer Amplifier,
RMS Converter, and A/D Converter.
CURRENT
SOURCE
0156
CR159
A/D CONVERTER
BUFFER
AMPLI Fl ER
OUTPUT
CR206
INTEGRATOR
------1..»----,
OUTPUT
+15 V
(D)
Buffer Amplifier positive overrange is controlled by CR 157,
CR158, 0158, R163, and R166; while negative overrange
is controlled by CR156, CR159, 0159, R164, R167, and
0162. Resistors R163-R166 and R164-R167 establish the
operating threshold on their respective transistors. When-
RMS
CONVERTER
INPUT
+5 V
R204
COUNTER
OUTPUT
PIN 8
U260
O190A
U250A
U250B
+15V(D)
VR188
UN BLANKING
TO
Z
AXIS
AMPLI Fl ER
0390
1481-13
Fig. 3-6. Overrange circuitry simplified schematic diagram.
3-8
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