9
Subject to change without notice
S h o r t D e s c r i p t i o n o f H M 3 0 3 - 6 B o a r d s
Short Description of HM303-6 Boards
Preliminary note:
This short description refers to the HM303-6 block diagram. It
contains the most important functions, but not all.
1 YP Board
1.1 CH1 and CH2
1.1.1 Input, High Impedance Attenuator and FET impedance
converter
The measuring signal at the input is connected to the AC/DC
coupling switch. O
pp
osite to DC coupling, in AC coupling mode
the DC signal content is blocked.
With GND not activated, the signal bypasses the GND (ground
switch) into a switchable high impedance (1 MΩ) attenuator
and enters a FET (impedance converter). If GND is selected,
the signal path is interrupted and attenuator or FET input are
grounded.
1.1.2 Pre-Amplifi er
The next stage is the Pre-Amplifier where an additional
amplifi cation by 5 is made to enable 1 mV/cm and 2 mV/cm
sensitivity.
1.1.3 Low Impedance Attenuator
The following selectable low impedance attenuators (1:1, 2:1
and 4:1); the high impedance attenuator and the Pre-Amplifi er
enable the selection of all Y defl ection coeffi cients from 1
mV/cm to 20 V/cm.
1.1.4 Variable Gain and Symmetry
In the next stage (VAR. GAIN) the fi xed Y defl ection coeffi cient
can also be set to uncalibrated intermediate values; unba-
lance can be compensated by variable balance adjustment
(VAR_BAL). Additionally the signal is converted in this stage
from an unsymmetrical signal into 2 symmetrical signals with
a phase difference of 180°. The following stages are designed
as two identical symmetrical amplifi ers.
1.1.5 Trigger Pick Off, Intermediate Amplifi er Driver and
Invert CH II
In this stage the trigger signal is picked off and feeds the In-
termediate Trigger Amplifi er. The signal at the emitter drives
the Intermediate Amplifi er (channel II via the Inverting Switch).
When activated, the Inverting Switch interchanges the 2 (180°
different) measuring signals to be amplifi ed in the following
stages. The result is a 180° turned (inverted) signal display.
Unbalance in the channel II stage can be compensated by the
invert balance adjustment (INV_BAL2).
1.1.6 Intermediate Amplifi er
This amplifi er follows the inverting switch. Here the DC current
of both identical amplifi ers is controlled in such a way, that if
the current in one amplifi er is reduced it increases in the other
amplifi er by the same amount. This causes a trace position shift
in (Y position). Time constants between both emitters are for
amplifi er frequency response correction.
1.1.7 Channel Switch
Thereafter the measuring signals of CH1 and CH2 are input
in the Channel Switch (diode switch) of each channel. Both
channel switch outputs are connected with the Y-Final Ampli-
fi er on XY Board.
1.1.8 Channel Switch Control
Depending on the current channel mode (CH I, CH II, alterna-
ting DUAL, cho
pp
ed DUAL, XY and CT (Component Tester)) the
channel switches are controlled by the Channel Mode Control
stage (IC2007). This IC also controls the trigger channel swit-
ches CH I, CH II (internal triggering) and external triggering
(TRIG. EXT.) and generates the cho
pp
er signal as well as the
cho
pp
er blanking signal.
1.2 Trigger Section
1.2.1 Intermediate Trigger Amplifi er CH I
The CH I measuring signal originating from the measuring
amplifi er (trigger pick off) is amplifi ed in this amplifi er (named
TRIG.-PICK-OFF in the circuit diagram). The same IC (2004)
acts as the Trigger Channel Switch CH I.
Amplifi er unbalance in this stage can be compensated by DC-
Triggering adjustment (P2006).
1.2.2 Intermediate Trigger Amplifi er CH II
The CH II measuring signal originating from the measuring
amplifi er (trigger pick off) is amplifi ed in this amplifi er (named
TRIG.-PICK-OFF in the circuit diagram). The same IC (2005)
acts as the Trigger Channel Switch CH II.
Amplifi er unbalance in this stage can be compensated by DC-
Triggering adjustment (P2008).
1.2.3 External Triggering
The signal for external triggering, originating from the TRIG.
EXT. input, passes a 2:1 divider and controls a FET (impedance
converter). In the next stage (IC2002) the signal is converted
from an unsymmetrical signal into 2 symmetrical signals with
a phase difference of 180° and enters the External Trigger
Channel Switch.
1.2.4 Trigger Source Selection
The Trigger Channel Switches are controlled by the Channel
Mode Control stage (IC2007). The signal to be used for trigge-
ring is output at one of the trigger channel switches, connected
with the Trigger Amplifi er (Sync. Amp.) on TB Board.
2 XY Board
2.1 CT Switch
If CT mode is selected the channel switches CH I and CH II are
closed and the Y component of the COMPONENT TESTER signal
is input via the CT Switch in the following Y-Final-Amplifi er.
2.2 Y Final Amplifi er
The measuring signal is amplifi ed and controls the Y plates of
the cathode ray tube (CRT).
2.3 TB XY CT Switch
This switch is controlled by the mode settings and has inputs
for the time base sawtooth signal, the X signal component in
XY mode and the X signal in CT (COMPONENT TESTER) mode.
One of these signals controls the X Final Amplifi er.
2.4 X Final Amplifi er & X-Pos. Control
The signal for X defl ection is amplifi ed and controls the X plates
of the cathode ray tube (CRT). The gain can be switched between
x1 and x10 X defl ection.
A DC voltage originating from X-POS. control is also input. It
enables X position shift of the trace.
