Theory Of Operation; Section Organization; Integrated Circuit Descriptions; Block Diagram Description - Tektronix 2246 1Y Service Manual

SECTION ORGANIZATION

This section contains general and detailed descrip­
tions of the 2246 1Y and 2246 Mod A Oscilloscope
circuitry. The Block Diagram Description describes
the general operation of the instrument functional
circuits. Each major circuit is explained in detail in
the Detailed Circuit Description. Schematic and
block diagrams show the circuit components and
interconnections between parts of the circuitry. The
circuit descriptions are arranged in the same order
as the schematic diagrams.
The detailed block diagrams and the schematic
diagrams are in the Diagrams section at the rear of
this manual. Smaller functional diagrams are in this
section near the associated text. The schematic
diagram associated with each circuit description is
identified in the text. For best understanding of the
circuit being described, refer to the applicable sche­
matic and functional block diagrams.

INTEGRATED CIRCUIT DESCRIPTIONS

Digital Logic Conventions
Digital logic circuits perform many functions within
the instrument. Functions and operation of the logic

INTRODUCTION

The Block Diagram Description gives an overview of
the schematic circuit functions (see Figures 9-4,
9-5a, and 9 -5 b ). It is provided as an aid in under­
standing the overall operation of the 2246 1Y and
2246 Mod A Oscilloscope circuitry before individual
circuits are discussed in detail. The Simplified Block
Diagram illustration shows the basic interconnec­
tions for signal flow and control signals. Schematic
diagram numbers that are referred to in the text are
shown by a diamond symbol in each block of the
figure.

THEORY OF OPERATION

BLOCK DIAGRAM DESCRIPTION

Section 3—2246 1Y and 2246 Mod A Service
circuits are represented by logic symbology and
terminology. Most logic functions are described
using the positive-logic convention. Positive logic is
a system where the more positive of two levels is
the TRUE (or 1) state; the more negative level is the
FALSE (or 0) state. In this logic description, the
TRUE state is high, and the FALSE state is low.
Voltages of a high or low state vary among individual
devices. For specific
common parts, refer to the manufacturer' s data
book.
Hybrids
The Channel 1 and Channel 2 attenuators and input
buffers are hybrid devices combining thick-film and
semiconductor technologies.
made with interconnected circuitry on a single
ceramic carrier and have improved performance
characteristics over a more discrete type circuit.
Linear Devices
The operation of individual linear integrated circuit
devices is described in this section using waveforms
or graphic techniques when needed to illustrate their
circuit action.
VERTICAL INPUTS (Diagram 1)
The signals for viewing or for triggering are applied
to the CH 1 through CH 4 vertical input BNC con­
nectors via coaxial cables or probes. Channels 1
and 2 have a choice of AC or DC input coupling or
GND. Channels 3 and 4 have DC input coupling only.
Scaling of the Channel 1 and Channel 2 input signals
has a range of 2 mV per division to 5 V per division
without the use of external attenuators. Channels 3
and 4 are limited to two input attenuator choices:
0.1 V per div and 0.5 V per div.
device characteristics of
These devices are
3-1