Tektronix 7B92A Maintenance Manual page 33

External Source (SN B069999-below). The external
trigger signal is connected to the Main Trigger Generator
through the MAIN TRIG IN connector, J100. The input
impedance at J100 can be set to either 1 megohm or 50
ohms by TERM switch S205.
If the SOURCE switch is set to EXT, relay K6
energizes and applies the trigger signal to C11 and R11.
Signals below 30 kilohertz are connected to the gate of
Q22A through R14, C12, R12, and R11.
between 30 kilohertz and 100 megahertz are connected
to the gate of Q22A through R17 and C11.
signals pass through Q22A and 024 to pin 3 of U64.
Signals above 100 megahertz are connected to pin 4 of
U64 through C20. (Pins 3 and 4 of U64 are internally
connected.) .
f the SOURCE switch is set to EXT ' 10, relay K6
deenergizes and applies the input signal to C10 and R9.
The signal is then divided by 10 before being applied to
the gate of Q22A.
Internal Source (SN B070000-above).
internal trigger signal from the vertical channel of the
oscilloscope is connected to the Main Trigger Generator
through J150. Signals below 30 kilohertz are amplified
by U44B and connected, along with the offset from the
LEVEL control, to pin 1 of U74 and to the base of Q86.
Signals above 30 kilohertz are coupled through C46 to
pin 14 of U74. (Pins 13 and 14 of U74 are internally
connected.)
Internal Source (SN B069999-below).
internal trigger signal from the vertical channel of the
oscilloscope is connected to the Main Trigger Generator
through J150. Signals below 30 kilohertz are amplified
by U128B and connected, along with the offset from the
LEVEL control, to pin 1 of U64 and to the base of 072.
Signals above 30 kilohertz are coupled through C46 to
pin 14 of U64. (Pins 13 and 14 of U64 are internally
connected.)
Internal-External
above). Amplifier U74 is a dual-channel, differential
amplifier with a common reference voltage for both
channels. The input channel to be amplified is selected
by the bias on pins 2 and 15. When R77 is connected to
-15 volts, the internal trigger signal (pins 13 and 14) is
amplified. When R79 is connected to -15 volts, the
external trigger signal (pins 3 and 4) is amplified. The
push-pull outputs (pins 8 and 9) are connected to the
inputs (pins 5 and 8) of U122.
When AC H F REJ coupling is selected, R77 and R79
are both disconnected from -15 volts, disabling U74.
The low-frequency signals (below 30 kilohertz) are then
connected to U122 through Q86 (internal signals) or 082
(external or line signals).
Signals
These
Amplifier (SN B070000-
Internal-External
below). Amplifier U64 is a dual-channel, differential
amplifier with a common reference voltage for both
channels. The input channel to be amplified is selected
by the bias on pins 2 and 15. When R66 is connected to
-15 volts, the internal trigger signal (pins 13 and 14) is
amplified.
external trigger signal (pins 3 and 4) is amplified. The
push-pull outputs (pins 8 and 9) are connected to the
inputs (pins 3 and 14) of U84.
When AC HF REJ coupling is selected, R66 and
R67 are both disconnected from -15 volts, disabling U64.
The low-frequency signals (below 30 kilohertz) are then
connected to U84 through Q72 (internal signals) or Q74
(external or line signals).
Slope Selector and Trigger Generator (SN
B070000above). U122 selects the slope of the input
waveform on which triggering occurs. If pin 3 is high, the
time base will trigger on the negative slope of an internal
The
signal or the positive slope of an external signal. If pin 3
is low, the time base will trigger on the positive slope of
an internal signal or the negative slope of an external
signal. (The internal signal is inverted by U74 or Q86
before being applied to U122.)
The delay mode control signal into U122, pin 4 is
functional only when the unit is operating as a delayed
sweep unit in the B horizontal compartment of a
mainframe with two horizontal compartments. When the
The
unit is operating in the Independent or Triggerable After
Delay Time modes (as determined by the delaying
sweep time-base unit in the A horizontal compartment),
there is no affect on the Trigger Generator circuits.
However, when the unit is operating in the B Starts After
Delay Time mode, a HI level at U122, pin 4 causes the
trigger IC to generate a gate pulse at pin 15 when the
trigger disable input goes low.
Slope Selector Amplifier (SN B069999-below).
Amplifier U84 selects the slope of the input waveform on
which triggering occurs. If pin 6 is high, the time base
will trigger on the positive slope of an internal signal or
the negative slope of an external signal. If pin 6 is low,
the time base will trigger on the negative slope of an
internal signal or the positive slope of an external signal.
(The internal signal is inverted by U64 or Q72 before
being applied to U84.)
The push-pull outputs (pins 7, 8 and 9, 10) of
U84 are connected to the inputs (pins 3 and 13) of U104.
Output
Amplifier U104 provides a final gain stage before driving
the trigger-output tunnel diodes. The push-pull output of
U104 (pins8 REV B, JUN 1978
3-2
Theory of Operation-7B92A
Amplifier
When R67 is connected to -15 volts, the
Amplifier (SN
(SN B069999-
B069999-below).