Final Amplifiers - Fluke PM3082 Service Manual

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An output signal from DTB TRIGGER FILTERS + AMPLIFIERS can be used for X DEFLection (MTB
and DTB are off then) via the block TIME BASE / X DEFLECTION INPUT CIRCUIT.
The function of DTB CURRENT SOURCE, DTB TIMING and DTB SAWTOOTH PICK OFF is
identical to the corresponding blocks in the MTB section. For the DTB LOGIC there is an extra input
signal START to start the DTB directly after the adjusted delay time. The START signal originates
from the MTB TIMING CONTROL.
The block AUTO CURSOR POSITION is used to position the voltage cursors automatically on the
top and bottom level of the signal. The top and bottom levels are detected via the DTB triggering: the
microprocessor scans the waveform by successively changing the DTB LEVEL and checking if
triggers are still detected. Automatic calibration of the X-path (including output circuit of DTB TIMING
CONTROL) is done with accurate voltages from the block X DEFLECTION CALIBRATION.
The DTB TIMING CONTROL is simpler than the corresponding block in the MTB. The functions
DELAY and HOLD OFF are not present. DTB uses the MTB hold off time. This is due to the fact that
the DTB can not run while the MTB does not.
X deflection selection and intensity control.
The block TIME BASE/X DEFLECTION INPUT CIRCUIT permits selection between horizontal
deflection via MTB/DTB or via a signal selected via the DTB triggering (X DEFL mode).
The block Z-CONTROL controls the intensity of the signal on the screen. This also affects the
focusing. Signal intensity and the intensity of text is determined in the final amplifier section.
The signal intensity is determined by the MTB LOGIC (light on/off) and DTB LOGIC (intensified part
during run of DTB). The ratio between intensity of MTB and DTB is determined by control signal
INTENS RATIO. Input signal CHP gives display blanking in vertical display mode chopped when
switching from one channel to another. The control signal TRACE INTENSITY is influenced by the
control with the same name. Intensity can also externally be controlled via input socket EXT Z MOD.
3.2.4

Final amplifiers

The final amplifier can be split up in parts for vertical (Y) and horizontal (X) deflection and parts for
intensity (Z) and focusing control. Input signals originate from vertical (Y) channels and time bases
(X and Z). The signals that determine X, Y and Z of the text originate from the text generator on the
microprocessor unit. The signal that switches between text and trace (SW signal) display originates
also from the text generator. The outputs of the final amplifiers drive the Cathode Ray Tube (CRT).
The various sections are explained now in sequence.
Vertical deflection.
The FINAL Y INPUT STAGE receives input signal for signal display (YS) from the DELAY LINE. A
second input signal (YT) determines the vertical component of the text information. The input signal
that comes from TEXT/TRACE SELECTION controls switching between text and trace display. The
HF SQ WAVE COMPENSATION is controlled by the microcomputer provides that signal distortion
from the DELAY LINE is compensated in the FINAL Y INPUT STAGE. The FINAL Y AMPLIFIER
drives the vertical deflection plates of the CRT. The voltage applied to these plates is measured by
the block CALIBRATE Y CIRCUIT. Its output signal YCAL is applied to the microprocessor; this is part
of the automatic vertical calibration facility.
Horizontal deflection.
The FINAL X AMPLIFIER DRIVER receives input signal for signal display (XS) from the Main and
Delayed Time Base sections. A second input signal (XT) determines the horizontal (X) component of
the text information. The input signal that comes from TEXT/TRACE SELECTION controls switching
between text and trace display. The FINAL X AMPLIFIER drives the horizonal deflection plates of the
CRT. The voltage applied to these plates is measured by the block CALIBRATE X CIRCUIT. Its output
signal XCAL is applied to the microprocessor; this is part of the automatic horizontal calibration
facility.
DESCRIPTIONS