Digitizer - Fluke Autoranging CombiScope PM3370B Service Manual

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The LINE IN voltage is applied to the LINE FILTER. This block prevents line interference from
entering the supply unit. Also interference generated by the power supply does not enter the mains.
An output signal of the filter is applied to the LINE TRIGGER PICK OFF in order to facilitate line
triggering of the time bases.
The other output signal is applied to RECTIFIER + SMOOTHING: the output of this block has a dc
voltage of which the height depends on the applied line voltage. This dc voltage is applied to the
FLYBACK CONVERTER. This block incorporates a high voltage switching element that converts the
dc voltage into a high-frequency ac voltage. This ac voltage is applied to the primary winding of a
transformer. The secondary winding has many taps with connected RECTIFIERS: this gives the
required supply voltages for the oscilloscope. The +5V POSTREGULATOR gives additional
stabilization of the +5V supply voltage.
Stabilization of the output voltages at different line voltages is achieved by varying the on/off ratio of
the switching element in the FLYBACK CONVERTER. The on/off ratio is determined in the
CONTROL CIRCUIT by comparing the accurate output voltage of the +10V REFERENCE SOURCE
and an output voltage of the RECTIFIERS.
The EHT CONVERTER generates the 6.3V heater voltage and -2.2kV cathode voltage for the
Cathode Ray Tube (CRT). The +14kV final accelerator voltage for the CRT is generated in the HIGH
VOLTAGE MULTIPLIER.
The AUXILIARY CONTROL is controlled by the microprocessor (µP) and generates three dc voltages
that are used for TRACE ROTATION adjustment, GRATICULE ILLUMINATION adjustment and
speed control for the FAN.
The PROTECTION CIRCUIT switches the power supply off in case of over and under output voltage,
too low line voltage and too high temperature.
3.2.7

Digitizer

Blockdiagram description of the digitizer unit A8, which contains all digital storage circuits of the
oscilloscope.
Main sections of the digitizer are:
- Input Stage
- Analog to Digital Converter and Clock Generator
- Control-signal Generator
- Trigger Comparator, Source Selector and Delta-t circuit
- Data Acquisition and Trigger Logic and Fast Acquisition Memory
- Main Acquisition Memory
- Digital Signal Processor and Program Memory
- Bus Arbiter and Trace Generator
- Text Generator and Text Memory
- X- and Y- Output DAC, Dotjoin circuit and Intensity Control
The digitizer unit contains a large number of integrated circuits that consists of a large amount of
functions. It is not possible to measure around inside these circuits and therefore a detailed
description of the functions in these integrated circuits is not given.
The functioning of the digitizer is explained using a separate blockdiagram.
In the blockdiagram description as much links as possible are made to the different components in
the circuit diagrams and their item numbers.
DESCRIPTIONS