Tektronix 3B5, Инструкция по эксплуатации

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Circuit Description — Type 3B5
Enable Multivibrator
For Seek Mode operation, Q815 and Q825 are coupled
as a bistable multivibrator. The multivibrator switches each
time an advance command is received from the Multiplier
Counter stage. The collector level of Q815 and Q825 deter­
mines which group of transistors in the Decade Counter can
conduct. At the start of the seek cycle, the seek mono pulse
from the Seek Circuit turns Q815 on through D818 and R818.
The collector of Q815 goes negative and the base level of
transistors Q755, Q765, Q775 and Q785 (B group) is pulled
negative to hold them off. The collector of Q825 rises posi ­
tive and Q855, Q865, Q875 and Q885 (A group) are
enabled. Only one of the transistors in the A group con ­
ducts, however (see Decade Counter discussion).
The third advance pulse from the Seek Circuit produces
an advance command to the Enable Multivibrator through
D81 1. This advance command turns off the on transistor.
For example, the first advance command (third advance
pulse) after the circuit has been reset is connected to the
base of Q815 through C812 and D814. Q815 turns off and
Q825 comes on. Now the B group transistors are enabled
and the A group is locked out. With the sixth advance pulse
to the Multiplier Counter circuit, the Enable Multivibrator
returns to the original condition and the A group transistors
are enabled. The Enable Multivibrator switches with each
third advance pulse produced by the Seek Circuit.
For External Mode operation, either Q815 or Q825 is held
on by the grounding external program enable logic applied
through terminal 23 or 24 of J30. This holds the associated
transistor on and locks out the corresponding group of
Decade Counter transistors. For example, external program
enable logic applied to terminal 23 (A logic line) holds
Q815 on. The collector level of Q815 goes negative to lock
out the B group transistors and allow the A group transistors
to conduct.
Decade Counter
The Decade Counter is an eight-state (alternate four-four)
ring counter which provides the decade logic levels in the
Seek and External Modes of operation. The transistors in
the Decade Counter are divided into two groups; Q755,
Q765, Q775 and Q785 form group B and Q855, Q865,
Q875 and Q885 form group A. Only one of these transistor
groups can conduct at one time as enabled by the Enable
Multivibrator. Furthermore, only one transistor within the
enabled group conducts as determined by the ring-counter
action.
The seek mono pulse from the Seek Circuit biases Q855
on. Also the Enable Multivibrator is reset as described
previously to allow the A group transistors to conduct. When
Q855 conducts, its collector level goes negative and it
reverse biases transistors Q865, Q875 and Q885 through
D862, D872 and D882. The 1 s decade (a) logic line drops
to —12 volts to select the 1 s timing decade. The Decade
Counter remains in this condition until the Enable Multivi ­
brator is switched by the advance command from the Multi ­
plier Counter (every third advance pulse from Seek Circuit).
Then, the opposite group of transistors is enabled; in this
example, the B group. As Q855 turns off, the positive-going
level change at its collector is coupled to the base of Q755
through C856 and R753. The collector of Q755 goes negative
to lock out the remaining transistors in the B group. The
decade logic output on the 0.1 s decade (b) logic line (0.1
second timing decade) is — 12 volts. This action continues
each time an advance command switches the Enable Multi­
vibrator. As the on transistor is switched off by the Enable
Multivibrator, it turns on the next transistor in the opposite
group. Decade logic from the output of the Decade Counter
is connected to the Readout Logic circuit. The alternate four-
four ring counter configuration just described is used to
insure that the ring counter does not free run as sometimes
occurs in conventional counters with this number of states.
For External Mode operation, external program decade
logic connected to terminals 6, 8, 9 or 11 of J30 controls
the Decade Counter. The grounding external program
decade logic is connected to the bases of the corresponding
transistors in both groups A and B. Only the transistor in
the group which is enabled by the Enable Multivibrator
conducts. For example, if the external program logic is con ­
nected to terminals 9 and 23 of J30 (0.1 ms or 10 ms decade
logic and A enable logic) the external program decade logic
is connected to both Q775 and Q875. However, the A
external program enable logic connected to the Enable
Multivibrator locks out the B group transistors so only Q875
can turn on. The decade logic output is on the 0.1 ms decade
(e) logic line to select the 0.1 ms timing decade.
Operating Mode Power
General
The Operating Mode Power circuit provides Seek/Manual
Power, Manual Power, Seek/External Power and External
Power to the unit. The output power from this circuit is
changed to control the operating mode. For example in
the Seek Mode of operation, Seek/Manual and Seek/
External Power output is available and in the External Mode
of operation Seek/External and External Power output is
available. Fig. 3-28 shows a logic block diagram of the
Operating Mode Power circuit. A diagram of this circuit
is shown on diagram 8 at the rear of this manual.
Manual Mode Control
In the Manual Mode of operation, Q915 determines the
output of this circuit. Fig. 3-29 shows circuit conditions for
Manual Mode operation. Q915 is forward biased by the
level at its base established by divider R91 1 -R912-R913.
This level is more positive than the level at the base of Q905
so that Q915 comes on when the unit is first turned on to
provide Manual Mode operation (except when programmed
for External Mode). The collector current of Q915 flows
through B915 and the MAN pushbutton lights up. This bulb
drops about 6 volts of the — 12-volt level at the collector
of Q915 to provide current to the — 6-volt line for the heater
of V 1 63. This current is supplied in parallel with the cu r-
rent from the s/DIV and UNCAL Readout Control stage.
Current also flows through K915 and K915-1 is actuated
to connect — 12.2 volts to the Manual Power line. Seek/
Manual Power output is provided through D919. The collector
level of Q915 is connected to the Seek Mode Control stage
through D901 to lock it off during Manual Mode operation
The Manual Mode of operation can be selected by pressing
the MAN button or by changing the sweep rate with the
MANUAL TIME/DIV switch. When the MAN button is
3-40