Shift Register 0 Bit Assignment - Tektronix 2246 1Y Service Manual

Pin
4
5
6
7
14
13
12
11
4
5
6
7
14
13
12
11
4
5
6
7
14
13
11
Input Coupling
Signals applied to the CH 1 BNC connector are
coupled to the CH 1 attenuator via the CH 1 Input
Coupling circuit. Switching logic for those con­
nections is shown in Table 3-2. Relay K100 switches
between direct (DC) and capacitive coupling (AC) of
the input signal; K101 switches between connecting
the applied input signal and the VOLT CAL signal to
the input of the attenuator. The VOLT CAL signal line
Theory of Operation—2246 1Y and 2246 Mod A Service
Table 3-1

Shift Register 0 Bit Assignment

Signal
U171
CH 1 GND
CH 1 AC
CH 1 X10 1
CH 1 X I 0 2
CH 1 XI
NOT USED
CH 1 X5
CH 1 PREAMP 1
U172
CH 1 PREAMP 0
CH 2 GND
CH 2 AC
CH 2 X I 0 1
CH 2 X I 0 2
CH 2 XI
NOT USED
CH 2 X5
U173
CH 2 PREAMP 1
CH 2 PREAMP 0
CH 2 INVERT
CH 3 PREAMP 1
CH 4 PREAMP 1
ZERO HYST
RO FREEZE
Controls
K101— CH 1 GND Coupling (last bit)
K100-CH 1 AC Coupling
K102—CH 1 X I 0 Attenuator 1
K103-CH 1 X I 0 Attenuator 2
K105—CH 1 X I Buffer Attenuation
No connection
K104—CH 1 X5 Buffer Attenuation
U210—CH 1 Preamplifier Gain
U210—CH 1 Preamplifier Gain
K108-CH 2 GND Coupling
K107-CH 2 AC Coupling
K109—CH 2 X I 0 Attenuator 1
K110-CH 2 X10 Attenuator 2
K112—CH 2 X I Buffer Attenuation
No connection
K i l l —CH 2 X5 Buffer Attenuation
U220—CH 2 Preamplifier Gain
U220—CH 2 Preamplifier Gain
U220—CH 2 Preamplifier Invert
U230—CH 3 Preamplifier Gain
U240—CH 4 Preamplifier Gain
U431C—B Trigger Comparator Hysteresis
U509C—Controls Readout for SELF CAL
(first bit loaded)
provides either the ground for GND Coupling in
normal oscilloscope operation or a test voltage input
for characterization during vertical SELF CAL.
With the Input Coupling set to GND (both AC and DC
off), the signal path is bypassed by C l 13. That
capacitor filters any noise from the VOLT CAL signal
line. There is no precharge of the input coupling
capacitor (Cl 12) when the coupling is in ground
(GND). Resistor (R111), in series with the BNC input,
is a damping resistor.
3-7