CHAPTER 3
CIRCUIT DESCRIPTIONS
3.1.1 This chapter wi
11
assist the reader to comprehend the
circuitry
of the OM64. By referring to the Block Oiagram
reference Figure 1 the reader will see the interfaces of the
various circuits and signal paths, which will be dealt with in
detaiI later.
3.1.2
The signal is fed via the Attenuator to the Vertical Am-
plifier. Its description covers the function of the 'Y' input
pre-amplifiers and Output amplifier, Channel switching multi-
vibrator and trigger pre-amplifier. The output is fed to the 'Y'
plates of the CRT with a portion of it being fed to the trigger
network.
3.1.3
The Trigger circuit provides pulses of suitable amplitude
and polarity to trigger the timebase from internally or ex-
ternally derived waveforms.
3.1.4
The Timebase description deals with the AL T pulse and
Sweep generators, Gating and Hold-off bistables. This stage
determines the start and finish of eachsweepand generatesa
sawtooth waveform for the horizontal amplifier.
3.1.5
The Horizontal amplifier description coversthe
'X'
output,
which amplifies the sawtooth waveform or an external
'X'
signal and applies it in push-pull to the
'X'
plates of the CRT.
3.1.6
The Unblanking amplifier description covers the Chop and
Sweep retrace blanking amplifiers. The output being fed to
the CRT g2 electrode.
3.1.7
The Calibrator and E.H.T. are included with the descrip-
tion on the Power supplies, the function of the former is to
provide a calibrated peak to peak squarewaveat power·line
frequency for the purpose of checking the vertical amplifier
and timebase calibration.
3.1.8
The
CRT
description covers the store and non store
switching,
manual
and
auto
erase generators, enhance
generator and collimation correction for the storage section
of the
CRT
Also included is a brief description of the
manner in which the CRT actually stores information.
The signals to be observed are connected to the instrument
via BNC sockets and switch S901, reference Figure 2. Two
identical
attenuators
each comprising
four
frequency-
compensated resistive dividers with ratios of 100: 1, 10: 1,
5:1 and 2:1. These are switched singly or in tandem; C902,
C905, C908 and C912 serve to standardize the input time
constants; C904, C907, C911 and C914 compensate the
respective dividers.
3.3
VERTICAL
AMPLIFIER
('Y'-AMPLI FI ER)
The circuits of channel 1 (CH1) and channel 2 (CH2) are
identical with zener diodes 0604, 0611 providing stabilized
positive and negative voltages and diodes 0607, 0608 the
shift voltages CH1 is described below reference Figure 3.
Where references are made to CH2, CH2 will be quoted.
3.3.1
The output
from the attenuator is fed to the gate of
TR601 via a protection circuit C601, C602, R601, R602a,
R602b,
and
R603
which
prevents excessive voltage
damaging the input FET.
3.3.2
TR601 and TR602 form a paraphaseamplifier with their
sources long-tailed through TR628. R624 provides variable
gain control. Compensation is provided by R625 for trace
movement caused by varying R624. R622 compensatesfor
supply voltage variation in conjunction with
R626,
R630,
R632 and 0604. Neutralization is effected by C604.
3.3.3
The output from the FET input stageis taken via emitter
followers TR603 and TR604 to a gain stage TR605 and
TR606. In the emitter circuit R617 sets the X1 channel gain
and R618 the X10. The collector outputs are connected to
the switching stage,TR609 and TR611, via emitter followers,
TR607 and TR608, which provide in push-pull the channel
trigger signal. The Miller capacities of the above gain stage
are neutralized by C603 and C609.
In CH2 the emitter followers TR624 and TR625 provide the
horizontal signal in the X-V mode.
3.3.4 TR609 and TR611 form a long-tailed pair with C606 and
R614 providing H.F. compensation. Their output
feeds a
shunt feedback amplifier
TR612 and TR613. The feedback
resistors are split into pairs, R644, R650 and R658 R661;
with
H.F. compensation being provided by C621, R656,
C619, R655, connected between the junctions of the above
pairs of resistors.
3.3.5
The output from TR612, TR613 is fed to the emitter
input of the output stage, TR752 and TR753, which drives
the 'Y' plates of the CRT Fig.8.
A portion of the output is taken via a balanceddivider, R771,
R773 and R772, R774 to switch, S751,which switches either
the above portion of the-signal or the channel signal from the
emitter followers, TR607 and TR608, to a long-tailed pair
TR755, TR757, which drive the Trigger circuit.
3.3.6
The CH2 output
from
TR624. TR625 also drives a
separate long-tailed pair. TR754, TR756 which acts as a
horizontal pre-amplifier in the X-Y mode. The X-V gainsare
equalized with
R787. The outputs from
TR754, TR756
collectors drive the diode switching matrix in the horizontal
output amplifier.
3.3.7
Channel switching is carried out by TR614 and TR615,
which act as a bistable in the AL T mode and a free-running
multivibrator in the CHOP mode the current being provided
via a long-tail TR616.
Summary of Contents for DM64
Page 1: ...PAHAMQELIAJP KO EHHKO KLA OPKN CA cUBA I31 I JQ H ...
Page 32: ......
Page 62: ......
Page 63: ......
