Theory of Operation— 2236 Service
BEAM FIND switch S390 adjusts output-amplifier bias
ing to limit the voltage swing at the crt plates. This keeps
the vertical trace within the graticule area for locating off
screen traces. With the switch in the normal out position,
the -8.6-V supply provides emitter current to the Amplifier
output stage through R261. When the BEAM FIND switch is
in, the direct -8.6-V supply to R261 is removed and emitter
current is now supplied through R261 and R262 in series.
This reduces the amount of available emitter current and
limits the amplifier dynamic range.
A/B Sweep Separation Circuit
The circuit composed of Q283, Q284, Q285, and associ
ated components provides a means of vertically positioning
the B trace with respect to the A trace during Alt Horizontal
Mode displays. During the B Sweep interval, the Sep signal
from the Alternate Display Switching circuit is LO and Q283
is biased off. This allows A/B SWP SEP potentiometer
R280 to affect the bias on one side of a differential current
source composed of Q284 and Q285. This supplies a dc
offset current to the Vertical Output Amplifier and changes
the position of the B trace on the crt screen.
During the A Sweep interval, the Sep signal is HI and
Q283 is turned on. The base voltages of Q284 and Q285
are then the same, and equal current is supplied to both
sides of the Vertical Output Amplifier so that no offset of the
A trace occurs.
TRIGGER AMPLIFIERS AND SWITCHING
The Trigger Amplifiers, shown on Diagram 3, provide sig
nals to the A Trigger Generator circuit from either the Verti
cal Preamplifiers, the EXT INPUT connector, or the power
line. The A&B INT switch selects either Channel 1 or Chan
nel 2 as the trigger source, and the A SOURCE switch se
lects between internal, line, or external trigger sources.
Internal Trigger
Signals from the Vertical Preamplifiers drive the Internal
Trigger Amplifier with channel selection determined by the
VERTICAL and HORIZONTAL MODE switches.
Trigger pickoff from the Preamplifiers is accomplished by
Q302 and Q303 for Channel 1, and Q327 and Q328 for
Channel 2. The circuitry associated with Channel 2 is the
same as that for Channel 1 except that it does not have a
trigger offset adjustment.
Signals from the Channel 1 Preamplifier are applied to
Q302 and Q303. These emitter-follower transistors each
drive one input transistor in U310, and the collectors of the
U310 input transistors in turn supply emitter current to two
current-steering transistors. The compensation and biasing
network connected to the emitters of the input transistors in
U310 is fixed for Channel 2 but not for Channel 1. Poten
tiometer R309 adjusts the emitter bias levels of the two in
put transistors so that dc offsets between channels can be
matched.
The base bias voltages of one transistor in each output
differential amplifier pair is fixed by the divider network com
posed of R321 and R322. The other base voltage is con
trolled by the Ch 1 Trig line from the Trigger Channel
Switch. When the Ch 1 Trig signal is HI, the transistors in
each output pair with the collectors connected together are
biased on and the other transistors are off. The collector
signal currents are equal in magnitude but opposite in polar
ity and signal cancellation occurs. If the Ch 1 Trig signal is
LO, the other transistors in each pair will be biased on and
an output signal will be developed across R314 and R315 to
drive the Internal Trigger Amplifier.
Internal trigger channels are chosen by the A&B INT
switch with the A SOURCE switch set to INT. The INT posi
tion of S392 reverse biases CR393 and CR399 to prevent
external trigger signals or the line trigger signal from reach
ing the A Trigger Generator. Signals from the Internal Trig
ger Amplifier are passed to the A Trigger Generator through
forward-biased CR372.
CHANNEL 1. For triggering from Channel 1, the A&B INT
switch is set to CH 1. The XY line connected to S555 will be
at ground potential and one input of U555B will be held LO
by CR556. The output of U555B will then also be LO and
the Channel 1 signal path through U310 will be enabled. The
Channel 2 signal path is disabled by the outputs of both
U555C and U565B being HI.
CHANNEL 2. For triggering from Channel 2, the A&B INT
switch is set to CH 2. One input each of U555C and U555D
will be LO and force both gate outputs LO. The LO from
U555C will enable the Channel 2 signal path through U335
and the HI outputs of U555B and U565C will disable the
Channel 1 path.
VERT MODE. When the A&B INT switch is set to VERT
MODE, trigger source selection is determined by the two
VERTICAL MODE switches. For all VERTICAL MODE
switch combinations except BOTH-CHOP, the V Mode T
line is HI. The inputs and outputs of U555B, U555C, and
U555D will all be HI, and triggering selection will then be
determined by the inputs of U565B and U565C that are con
trolled by U540A in the Channel Switch circuit.
3-8
Summary of Contents for 2236
Page 10: ...2236 Service viii The 2236 Oscilloscope ...
Page 74: ...Theory of Operation 2236 Service 3 30 ...
Page 102: ...Performance Check Procedure 2236 Service 4 21 Figure 4 1 Test setup for DMM common mode check ...
Page 242: ...2236 Service 4204 34 Figure 9 6 CTM basic block diagram ...
Page 243: ...DMM POWER S U P P LIE S 2236 Service F ig u re 9 7 C T M d e ta ile d b lo c k diag ram ...
Page 254: ...S I 0 O I 5 1 S O i 4204 21 C IR C U IT BOARD INTERCONNECTIONS ...
Page 267: ...1 2 3 4 5 6 7 8 9 J T K L M_ _ ___ N___l _ P____l S ...
Page 271: ...1 2 3 4 5 6 7 8 9 lO P2SO O U1 A TRIGGER V T O W2500 5 A 223 R E V A P R W G ...
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Page 313: ...2236 Service T O U I 3 0 0 4 8 K T O UI300 II S K 0 2 2 3 6 Z Z O A Z 2 OPTION IA ...
Page 317: ...A 10 C O U N T E R T IM E R M U L T IM E T E R B O A R D A D J U S T M E N T LO C A T IO N S ...
Page 319: ...2236 Service TROUBLESHOOTING GUIDE 4206 99 4204 69A ...
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Page 324: ...2 REV APR 1986 ...
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