Theory of Operation—2445 Service
Table 3-1
Intensity Control
Type
of
Horizontal
Selects
Resulting Current
at BRIGHT
Display
HSA
HSB
Output
X /Y
LO
LO
Dl (display intensity) only
A Sweep
LO
HI
Dl + A Swp DAC current
B Sweep
HI
LO
D l + B Swp DAC current
Readout
HI
HI
ROI (readout intensity) only
The readout intensity (ROD level, controlled from the
front-panel READOUT INTENSITY pot, is conditioned
by
U350A and associated components. Operational
A m plifier U350A, configured as a full-wave rectifier,
increases readout intensity when the pot is rotated either
direction from center. Resistor R360 sets the minimum
readout intensity current that occurs at the m idpoint of the
READOUT INTENSITY pot rotation.
Readout On-Off Comparator U350B detects to which
side of center the READOUT INTENSITY control is set.
The Microprocessor reads the output of omparator U350B
via Status Buffer U2108 (diagram 2) at regular intervals.
Depending on the status received, the processor sets up the
Readout circuitry (diagram 7) to display either all of the
readout information or just the "delta ty p e " readouts.
Blanking of the crt display during CHOP VERTICAL
MODE displays or when switching between dot positions
in the readout displays is controlled by the Display
Sequencer's BLANK output (pin 3). When the signal is LO,
the crt z-axis is turned on to the selected intensity level;
when HI, the crt display is blanked.
READOUT CONTROL. Readout displays are controlled
by th e readout request (ROR) signal, the readout active
(ROA) signal, and the readout blank (ROB) signal. During
the first part of the holdoff time, up until one or two hold-
o ff ramps before holdoff time ends (dependent on the
sweep rate), the Display Sequencer sets the ROA signal
line LO. While the ROA line is LO, the Readout circuitry
may display readout character dots if necessary. During
readout displays, the horizontal and vertical select signals
(HSA, HSB, VS1, VS2, VS3, and VS4) are all set HI. This
deselects the waveform-related sweep and deflection signals
and gives display control to the Readout circuitry. While
readout information or cursors are being displayed, the
BLANK output signal (pin 3) is controlled by the readout
blank (ROB) signal from the Readout circuitry, and the
readout intensity (ROI) signal (pin 23) controls the
BRIGHT output level.
During holdoff, the Display Sequencer always sets
the readout active (ROA) line LO. As previously described,
setting the ROA signal LO allows the Readout circuitry
to display readout dots. In some settings of the SEC/DIV
switch, w ith adequate trigger rates, holdoff time is provided
fo r the Readout circuitry to display all the readout infor
mation w ithout causing noticeable display flicker.
In those cases where the holdoff time is insufficient
to prevent flicker, a portion of the Readout circuitry w ill
request display control by setting the readout request
(ROR) signal LO. The Display Sequencer recognizes all
readout requests immediately and switches the horizontal
and vertical select lines to the readout display mode. The
Readout circuitry displays one readout dot and then resets
the readout request HI to switch back to the display of
waveforms. Readout requests occur as required during
sweep times to keep the readout display caught up. (See
"R eadout" description fo r further information).
TRACE SEPARATION. The TRACE SEP feature is
used to position the alternate B Delayed Sweep trace down
ward from the A Sweep when Alternate Horizontal Display
Mode (TURN-ALT) is active. It is also used when either
the A t or 1 /A t measurement function is used w ith B Sweep
only displays. In the latter case, the TRACE SEP control
vertically positions the trace(s) associated w ith the A
control.
When the Display Sequencer determines that trace
separation should be active, the LO TSIN level at pin 7 is
routed to pins 9 and 8, the TS1 and TS2 outputs (con
nected together). This LO output turns o ff transistor
Q600 (diagram 6), thereby enabling the trace separation
voltage from the front-panel TRACE SEP pot to be applied
to pin 42 of Vertical O utput A m plifier U600. To disable
the trace separation function, the Display Sequencer sets
the TS1 + TS2 control line HI, turning on Q600 and
shunting the trace separation signal to ground.
X10 MAG SELECT. The MAG (sweep magnifier) output
(pin 39) drives the magnifier control input (pin 14) of
Horizontal O utput hybrid U800 and the select input
(pin 9) of analog switch U860C (diagram 6). Analog switch
U860C routes a magnifier gain-control voltage to the
Horizontal Am plifier to set the horizontal gain for the X I 0
magnified displays.
Summary of Contents for 2445
Page 1: ...Tektronix 2445 OSCILLOSCOPE SERVICE INSTRUCTION MANUAL ...
Page 11: ...2445 Service 3829 01 The 2445 Oscilloscope ...
Page 44: ...Theory of Operation 2445 Service 3831 10A Figure 3 1 Block diagram ...
Page 45: ...Theory of Operation 2445 Service 3831 10B Figure 3 1 Block diagram cont 3 3 ...
Page 210: ...3829 58 Figure 9 4 2445 block diagram ...
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Page 219: ...2445 382 72 ...
Page 222: ...2445 ...
Page 231: ...A 1 t C t t F t G t H t ...
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Page 247: ...A 1 C _____ D E F G H J 2445 3811 74 ...
Page 248: ...1 2 3 4 5 6 7 8 9 i o 2445 DISPLAY SEQUENCER TRIG GERING A4B SWEEPS ...
Page 253: ......
Page 263: ... 0 2445 J8 i S ...
Page 264: ...1 2 3 4 5 6 7 i 8 I i 9 10 2445 READOUT ...
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Page 283: ... 8VJNR EG 3S 5 fROM P232 5 10 A 15VUNREG 8S F R O Mn i 2445 3 0 2 S 8 I ...
Page 286: ...2445 3823 82 ...
Page 290: ...B H le w o q 87V T S o I R v n i U1 R1873 PARTIAL A9 HIGH VOLTAGE BOARD 2445 ...
Page 299: ...2445 Service DAC REF A5 CONTROL ADJUSTMENT LOCATIONS 3 ...
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Page 304: ...2 R E TU R N T O 1 ...
Page 305: ...ERROR MESSAGE DIAGNOSTICS ...
Page 306: ...ERROR MESSAGE DIAGNOSTICS ...
Page 307: ...O A A C t rnra g i tiw c t 3829 89 ...
Page 308: ...RETURN TO ...
Page 309: ...FRONT PANEL TROUBLESHOOTING ...
Page 310: ...FRONT PANEL TROUBLESHOOTING ...
Page 311: ...2445 Service 3829 90 ...
Page 316: ...R E TU R N T O v 1 y ...
Page 317: ...SWEEP TROUBLESHOOTING PROCEDURE ...
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Page 324: ...2445 Service 3829 85 ...
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Page 326: ... KERNEL NOP DIAGNOSTIC PROCEDURE ...
Page 327: ...10 POWER SUPPLY TROUBLESHOOTING PROCEDURE 3829 94 ...
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Page 334: ...2445 Service REGULATOR TROUBLESHOOTING PROCEDURE 3829 93 ...
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