Vertical Attenuators; Table Of Attenuator Settings; Input Coupling; High Impedance Accenuator - Philips PM3055 Service Manual

4-1
4.
ATTENUATOR
UNIT
(A1)
4
.
1
VERTICAL ATTENUATORS
The A and
B
channel attenuators are identical:
therefore only channel
i
is
described.
All relay and FET switches are controlled by the
microcomputer via
the
l^C bus. The
TEA
1017 converts this serial
DATA into
the
parallel
control signals
for all
relay or FET switches. A
list of the control
lines for all attenuator settings
is
given in the table below.
o
MAT2227
Figure 4.1 Table of attenuator settings
The channel A attenuator consists
of in five stages:
Input coupling
,
where depending on
the
relay KlOOl position,
the
input signal can either be d.c. -coupled (relay activated) or a.c.-
coupled (relay not activated).
High impedance attenuator with three attenuator stages
for the
xl
,
xlO and xlOO attenuation. The
l.f.
part of each stage
is
split via
a
resistor divider and routed via NlOOl
and V1019
to the
output of this
stage, where
it is
re-connected with the h.f. part of the input signal.
Potentiometers R1036 (TRACE
jump) serves
as a
offset compensation
for
NlOOl.
RELAY FET TRIMMER FOR
L.F.
SQUARE WAVE
L.F.
RESISTOR
DIVIDER
X
1
K1004
VlOll C1033
—
X 10 K1003 V1006 C1029 R1007-R1011
xlOO K1002 V1003 C1023 R1019-R1004
Note
that,
\dien
"0" (GND-A)
is
selected, the output
is
connected
to
ground via FET V1016 and
all
other relay- and FET switches are switchec
off.