Circuit Description—4 5 5 /A 2 /B 2
changing from one line voltage to the other, the line fuse
should be changed as follows: 1 amp fast blow fo r 116
volts or 0.5 amp fast blow fo r 232 volts.
The unused windings (pins 5, 6, 18, 19, 20, 21, and 22)
o f T700 are provided fo r use w ith instrument options.
Secondary Circuit
Integrated circuits U722A, U722B and U762 are high-gain
amplifier cells w ith differential inputs. These amplifiers
m onitor voltage variations in the o utput voltages and provide
correction signals to the series-regulating transistors.
Current lim iting circuits provide short-circuit protection for
each of the regulated supplies. The following te xt discusses
the +32 volt current-lim iting circuit. The other current-
lim iting circuits operate similarly.
In the +32 volt supply, Q734 is normally biased off. Under
normal conditions the base of Q734 sets at about +32 volts.
As the supply current increases, the voltage drop across
R734 increases. This increasing voltage is coupled through
Q736 to voltage divider, R732 and R733, causing the base
o f Q734 to go more positive. When the supply current in
creases sufficiently beyond the normal operating current,
Q734 turns on. The collector o f Q734 moves in the negative
direction, which begins turning o ff Q732 and Q736, and
creates a fold-back condition. See Figure 4-2. Transistor
Q736 continues to conduct some current when the supply
is limited, which drops enough voltage across R734 to keep
Q734 biased on. Resistor R731 acts to keep the minimum
fold-back current constant as the input line voltage changes.
The series regulating element in the —5 volt supply is a type
of Darlington configuration, consisting of Q766, Q768 and
K i l l .
Transistor Q768 is the current carrying element and
Q766 is the controlling element. The five diodes CR762,
CR763, CR764, CR765 and CR766 provide a level shift with
little attenuation o f the error signal.
Fuses F736, F746 and F768 provide short-circuit protection
fo r each o f the unregulated supplies.
Disconnect-Jumper wires are located in series w ith the
regulated voltage lines fo r use in troubleshooting.
Line triggering signal is taken from pin 17 o f T700 through
resistive divider R772-R773.
Capacitor C773 is provided
to reject unwanted high-frequency signals.
The SCALE ILLU M control, through Q784, varies the
voltage across the graticule lights DS784 and DS786 from
0 to 6.6 volts.
Fig. 4-2. Foldback circuit action.
4-6
REV. A, OCT 1975
Summary of Contents for 455
Page 1: ...Tektronix 455 A2 B2 PORTABLE OSCILLOSCOPE WITH OPTIONS I N S T R U C T I O N M A N U A L ...
Page 9: ......
Page 13: ...455 A2 B2 x 455 A2 B2 Portable Oscilloscope ...
Page 61: ...Circuit Description 455 A2 B2 Fig 4 4 Channel switching gates REV A OCT 1975 4 9 ...
Page 66: ...Fig 4 6 Sweep generator 1C Function block diagram Circuit Description 455 A2 B2 ...
Page 80: ...Maintenance 455 A2 B2 BOTTOM FRAME Fig 5 7 VO LTS DIV switch disassembly 5 8 REV A OCT 1975 ...
Page 90: ...Maintenance 455 A2 B2 Fig 5 13 Troubleshooting chart 5 18 REV A O CT 1975 ...
Page 91: ...Maintenance 455 A2 B2 1907 1 A Fig 5 13 Troubleshooting chart cont REV A OCT 1975 5 19 ...
Page 132: ...Instrument Options 455 A2 B2 Option 7 Page 8 REV E AUG 1979 D C TO AC I NVERTER ...
Page 166: ...l 07 7 REV b NOV C M1 4 5 5 MAIN MODULE BLOCK DIAGRAM ...
Page 167: ...4 5 5 A 2 B 2 AS VERTICAL MODULE IR07 R8 RE V B M O ...
Page 168: ...I S 0 7 9 8 R E V B NOV IRT7 A2 VERTICAL MODULE BLOCK DIAGRAM ...
Page 169: ...REV B NOV 1977 Fig 9 2 A1 Partial Interface board compo ...
Page 170: ...455 A2 B2 Sea Parts List for serial number ranges tial Interface board component locations ...
Page 173: ...v I m B 2 HORIZONTAL MODULE BLOCK DIAGRAM ...
Page 174: ...455 A2 B2 REV B NOV 1977 Fig 9 3 A 1 Partial Interface board component locations ...
Page 182: ...455 A2 B2 Fig 9 4 A20 Vertical board component locations SN B0110 ...
Page 185: ...455 A2 S2 4 5 5 M A fN M O DULE ...
Page 187: ...455 A2 B2 Fig 9 5 A20 Vertical board component location SN B010100 B REV C NOV 1977 ...
Page 191: ...V O L T S 01 ...
Page 192: ...V O LT S Q IV S H O W N IN 57 H V ...
Page 198: ... U 1 X SlCjMAt TO P2 A4 h o p it MODULE SEE PARTS LIST FOR SEMICONDUCTOR TYPES f SWITCHING ...
Page 207: ...A 1 4 B T I M I N G S W I T C H B O A R D A13 A TIM ING SWITCH BOARD 1 9 0 7 3 ...
Page 209: ...4 5 5 A 2 B 2 B 2 h o r iz o n t a l m o d u l e R o i I 11 R E V C NOV IS77 ...
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Page 216: ...A B T IM IN G S W IT C H INTERFACE C O N N E C T O R ...
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Page 224: ...455 A 2 B 2 ...
Page 225: ... 455 A2 B2 ...
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Page 234: ...455 A2 B2 ...