Block Diagram Description; Introduction - Fluke Autoranging CombiScope PM3370B Service Manual

DESCRIPTIONS
Some important notes:
- To measure some signals, it is necessary to unlock units. Refer to chapter 8.5 for details on how
to proceed.
- The given AC and DC signals are average values: your oscilloscope under test may deviate from
the values given in the circuit diagrams. 100 MHz clock signals and fast switching signals on the
digitizer unit A8 require a measuring oscilloscope with a bandwidth of 200 MHz or more.
- Although the oscilloscope is in standard setting, it may be necessary to do manual selections for
certain measurements. To measure e.g. the delayed time base and its triggering, it is necessary
to activate DTB and to select a channel as DTB trigger source.The same is valid for digitizer
functions like logic pattern, timed pattern, double sampling speed (250 ns/div).
- When measuring in the final amplifiers, it advised to switch off all text. This gives 'cleaner' signals
at the outputs. The text is written inbetween the signal at a random basis.
- Measuring the outputs of the final Y amplifier must be done with a 10 kΩ resistor between probe
tip and signal. This avoids oscillations.
- Refer to chapter 8.11.4.7 (Repair tools/DAC) on how to check the range of DAC-generated
adjustment voltages.
3.2

BLOCK DIAGRAM DESCRIPTION

3.2.1

Introduction

This block diagram and description are based upon the most complex version of this family of digital
oscilloscopes. Therefore there may be minor differences between your oscilloscope and the block
diagram and its description. Where differences may occur it is mentioned in the text.
The item numbers of active components are indicated each block of the diagram. This facilitates to
make the link with the circuit diagrams.
The oscilloscope is controlled by a microprocessor that connects to many blocks. Therefore
throughout this block diagram CONTROL CIRCUITS can be found that are controlled by the
microprocessor. The output signals can be simple on/off signals e.g. to switch a certain vertical
channel on and off. There are also adjustable dc voltages e.g. to determine the gain of a vertical
channel. Blocks that are under control of the microprocessor have the input signal "µP". In the
vertical, horizontal and time base sections, circuits are added for microcomputer controlled automatic
calibration.
This description is divided according to the functional blocks that can be distinguished:
- Vertical channels: there are 4 vertical channels (part 1).
- Triggering and time bases: there are sections for main- and delayed time base (part 1).
- Final amplifiers: for vertical (Y) and horizontal (X) deflection, intensity (Z) and focusing contro (part 2)l.
- Front unit and microprocessor unit (part 2).
- Power supply unit (part 2).
- Digitizer unit (part 3).
Also the printed circuit boards (units) are indicated in the blockdiagram. These units are:
- Signal unit A1: is the largest of all and incorporates 4 vertical channels and main- and delayed
triggering and time base.
- Final XYZ amplifier A2: all final amplifiers are present here. A separate part is connected to the
CRT socket.
- Microprocessor unit A3.
- Front unit A4: incorporates most of the rotary knobs and keys.
- CRT controls unit A5: incorporates the rotary knobs for the display functions.
- Power supply unit A6: supplies various voltages to the other circuit boards.
- Digitizer unit A8: includes all digital storage circuitry.
- Motherboard A10: many signals are routed via this unit.
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