Introduction; Control Unit; Attenuator Unit - Philips PM3055 Service Manual

3-10
3.2
BLOCK DIAGRAM DESCRIPTION
(see figure 3.1).
3.2.1 Introduction
This block diagram description
is
based around
all the
important
functional blocks and their interconnections.
The
interconnections
between
all p.c.b.'s are given
in the
interconnection diagram
of
figure
14.5. In
order
to
assist
in
cross-reference with
the
circuit
diagrams,
the
blocks include the item numbers
of
the active components
they contain.
Furthermore,
the
blocks are grouped together per printed-circuit
boarc
or
a
part of
it.
To
facilitate reference,
the names
of the functional
blocks
are given in text in CAPITALS.
Signal waveforms are also indicated
at
block interconnections where
useful
.
In this instrument almost
all the switches (UP-DOWN controls, softkeys
and
potentiometer UNCAL switches) influence
the
oscilloscope circuits
via
a
microcomputer
(uC)
system.
3.2.2
Control unit
Because
the
functional description
of the
control unit (see chapter
1C
is
almost simular
to
the
blockdiagram description,
no specific
attention
is
given
in this chapter
to this unit,
3.2.3 Attenuator
unit
The vertical channels A
and B for the signals
to
be displayed
are
identical. Each channel comprises an input SIGNAL COUPLING for AC/DC,
a
HIGH IMPEDANCE ATTENUATOR which gives
a
grounded
input or
a
signal
attenuation
of
xl-xlO
or xlOO, an IMPEDANCE CONVERTER,
a
LOW IMPEDANCE
ATTENUATOR which
gives signal attenuation of xl-x2,5 or
x5 and a
GAIN
xl-xlO
AMPLIFIER block, incorporated with
the CONTINUOUS CIRCUIT. This block
has
a
variable
gain, influenced by
the
front-panel VAR control. The
gain
is
also increased by xlO in order
to
obtain 2-5 and
lOmV settings
Similar
to
the
vertical channels,
the
external channel attenuator
alsc
has an input SIGNAL COUPLING, HIGH IMPEDANCE ATTENUATOR and IMPEDANCE
CONVERTER
in line.
However,
the
external channel has only
xl
attenuation
and no LOW IMPEDANCE ATTENUATOR.
The output of the
external channel
is
fed to
both MTB
and DTB TRIGGER PRE-AMPLIFIERS
,
All blocks that are capable
of
working
in different modes
are
controlled
by the control A
or
control
B
signals. These signals are
generated by the
CH.A CONTROL
or
CH.B CONTROL blocks.
3.2.4 Pre-amplifier
unit
This unit incorporates
the signal splitters for the vertical channels
and
B,
the
trigger view amplifier,
the
trigger circuits
for the
MTB
an
DTB and
the
chopper oscillator circuit. All these functions
are
controlled
by the control XYP and control XYA signals, generated by
the X-Y CONTROL blocks.