TRIGGERED OSCILLOSCOPE This easy-to-fo llow design lets you keep cost low by using a CRT of your choice. Its operational feature is a continuous zero basel ine. DANIEL METZGER and DENNIS PERRY .... CD co a SOURCE FOLLOWER 03 0 5 RETRIGGER HOLDOFF 1002 RETRACE SUPPRESSOR SWEEP GENERATOR 0 304 IC301 triggering. A Schmitt trigger produces squarewaves in sync with the input sig- nal, and a differentiator produces sharp spikes from the edges of the square- waves. The negative spikes initiate a lin- ear ramp that always starts at the same selected point on the input AC wave- - .... , r - BASELINE: GEN -- -' , I' I' BASELINE UJT I TRIGGER I FLIP-FLOP BASELINE ' SYNC AMPLIFIER 'I 0 307 OSCI LLATOR J4r"--=. 0 20 1 , I 0308 03 06 I 0 20 2 LL_-_-_-_-_-_-_-_- SWEEP SYSTEM .------, r-- - - -- --- - - - - - - - - - - - - - - - - - - ---, I VERTICAL AMPLI FIER I : .<:::tr VERTI CAL BASELINE SOURCE LOW -LEVEL I Dg I PT SWITCH FOLLOWER DIFFERENTIAL .c: I NU 0203 AMPLIFIER IV-- I ATT EN UATOR 0204 0 205 0206 , 0207 0208, 0209 , L ---- -- J HORIZONTAL AMPLIFIER IExT H OR ------ --- - :I ,-- - --, I IN HIGH-LEVEL , I @-o SOURCE DIFFERENTIAL I I FOL LOWER AMPLIFIER I , 02 10 021 1, 02 12 I L ...J r--- I I , , I I I I SOURCE , EXT @--o FOLLOWER , TRIG 0 301 L -, ,...-__ P .., OWER SUPPLY I -9 00 VOLT I SUPPLY 0 101 - 0113 I I I NOTE: SERIES 10 0 COMPONENTS ON POWER I SUPPLY BOARD; SERIES 200 ON THE I AMPLIFIER BOARD AND SERIES 300 PARTS I BOA '::D__ ...J FIG. 1- BLOCK DIAGRAM of the zero-baseline scope. Operation is somewhat similar to a dual-trace scope with the baseline considered as the second tr ace . proximately 3 ms each 15 ms, thus pro- viding a 1/5 duty-cycle baseline display at a rate of abo ut 60 Hz-too fast for the eye to perceive the flicker. A separate trigger amplifier is fed from a point ahead of the electronic baseline switch to preserve continuity of sweep ONCE A TECHNICI AN HAS EXPERIENCED tro ubleshooting with a calibrated DC lab scope, he'll probably want to keep that scope probe close at hand most of the time he's at the service bench . Tran- sistor base-emitter voltages, collector saturation voltages, and IC logic levels can be checked as easily as power-supply lines while the operating signals are present. No other instrument provides that simultaneous readout of bias and signal conditions. . Two factors have conspired to keep that scope probe out of the hands of most experimenters. The first is cost, which approaches $200--e ven for a kit. That problem is easily solved by sim- plified design . The scope described here can be built from standard parts for $100, and considerably less if the junk box is well stocked. Yet it boasts a 2- MHz bandwidth and 10mV-per-division vertical sensitivity. The second factor is the annoyingly frequent need to lay down the probe, reach over to the scope, throw the input switch from DC to GRO UND, check the position of the zero-volt baseline, and throw the switch back to DC. That prob - lem is handled by incorporating a circuit that prov ides a continuous display of the DC ground level at a brightness level lower than that of the signal display. How it works The operation of the scope as a whole is best understood from the block dia- gram , Fig . I. The vertical attenuator and amplifier provide a replica of the input signal, both AC and DC, at the approxi- mately lOO- volt level needed at the de- flection plates of the CRT. The electron- ic baseline switch interrupts the signal and grounds the amplifier input for ap- 39
11
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TRIGGERED OSCILLOSCOPE - files.domcxem.rufiles.domcxem.ru/infocenter... · triggering. A Schmitt trigger ... I ' BASELINE UJT I ... approximately 60 Hz is synchronized to the sweep
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TRIGGEREDOSCILLOSCOPE
This easy-to-fo llow des ign lets you keep cost low by using a CRT of yourchoice. Its ope rat ional feature is a continuous zero basel ine.
DANIEL METZGER and DENNIS PERRY
....CDcoa
SOURCEFOLLOWER
03 0 5
RETRIGGERHOLDOFF1002
RETRACESUPPRESSOR
SWEEPGENERATOR
0 304IC301
triggering . A Schmitt trigger producessquarewaves in sync with the input signal, and a differentiator produces sharpspikes from the edges of the squarewaves. The negative spikes initiate a linear ramp that always starts at the sameselected poin t on the input AC wave-
-...., r - BASELINE: GEN - - -',I'I ' BASELINE UJT I
0101 - 0 113 III NOTE: SERIES 10 0 COMPONENTS ON POWERI SUPPLY BOARD; SERIES 200 ON THEI AMPLIFIER BOARD AND SERIES 300 PARTS I~~ ~N.-:'~ E!. ~ND_B~E.:.I~ BOA'::D__ ...J
FIG. 1- BLOCK DIAGRAM of the zero-baseline scope. Operation is somewhat similar to a dual-tracescope with the baseline considered as the second tr ace.
proximately 3 ms each 15 ms, thus providing a 1/5 duty-cycle baseline displayat a rate of abo ut 60 Hz-too fast for theeye to perceive the flicker.
A separate trigger amplifier is fed froma point ahead of the electronic baselineswitch to preserve continuity of sweep
ONCE A TECHNICIAN HAS EXPERIENCED
tro ubleshooting with a calibrated DClab scope, he'll probably want to keepthat scope probe close at hand most ofthe time he's at the service bench . Transistor base-emitter voltages , collectorsat uration voltages, and IC logic levelscan be checked as easily as power-supplylines while the operating signals arepresent. No other instrument providesthat simultaneous readout of bias andsignal conditions. .
Two factors have conspired to keepthat scope probe out of the hands ofmost experimenters . The first is cost,which approaches $200--even for a kit.That problem is easily solved by simplified design . The scope described herecan be built from standard part s for$100, and considerably less if the junkbox is well stocked. Yet it boasts a 2MHz bandwidth and 10mV-per-divisionvertical sensitivity.
The second factor is the annoyinglyfrequent need to lay down the probe,reach over to the scope, throw the inputswitch from DC to GRO UND, check theposition of the zero-volt baseline , andthrow the switch back to DC. That problem is handled by incorporating a circuitthat prov ides a continuous display of theDC gro und level at a brightness levellower than that of the signal display.
How it worksThe operation of the scope as a whole
is be st understood from the block diagram, Fig . I. The vertical attenuator andamplifier provide a replica of the inputsigna l, both AC and DC, at the approximately lOO-volt level needed at the deflection plates of the CRT. The electronic baseline switch interrupts the signaland grounds the amplifier input for ap-
39
TO INPUTOF VERTICALAMPLIFIER
(Fig .31
TO INPUT OF.. HORIZONTAL
AMPLIFIER
(Fig.31
S402- b
.0 4
o .10.4
o I4
010
IMEGR404
HORIZONTALV/DIV
10
r ------TNPUT 1I RA CA~ FREO II (R405 COMP II TO 6·60 (C405I R4091 pF
cJ891I
I I
I RB(C410
I
I(R410 CB TO I
TO C4141 II R4141 II IL_____-:______ .J
ONE OF FIVE
o
o C404o 10pF
o
3 It RG-5B/U
S402-0
R402162K1%
R401B06K1%
R40340.2K
1%
C402100pF
EXTERNAL J2 r-- --<:--+-- SWEEPOUT'''!T----.--....-----.. IN~ FROM R325HORIZONTAL IN \0
J3 ~~~6PF.4" LINE EXT
~ r--+--4----;1;>2 S~3-b ~
V/DIV RA RB CB.0 4 IMEG
.1 604K 402K 62pF.4 909K lOOK 250pFI 953K 40.2K 625pF4 IMEG 10K .0025"F10 I MEG 4.02K .00621'F
RA AND RB - 1/2 WATTI % RESISTORS
C401.0 5" F
t-E60~AC
JIVERTICAL 0 DCINPUT -: S401-0
DCGND
OPTIONAL XIO PROBE
C41510pF
form . That ramp is applied to the horizont al amplifier to produce the calibrated time sweep . A source-followerprovides a low output impedance for theramp, an d an op-amp comparator holdsoff further triggering signals until theramp voltage returns to zero.
An au to-trigger circuit senses whenthe Schmitt trigger is not switching andimmediately applies a voltage to theramp genrator commanding continuousramps, thu s providing sweeps for thedisplay of DC voltages.
A UJT baseline osc illator running atapproximately 60 Hz is synchronized tothe swee p generator to insure that theswitching from signal to baseline willalways occ ur during a retrace of thesweep. The baseline flip-flop drives thebaseline-switch ing FET' s at the input ofthe vertical amplifier.
The CRT cathode is operated at -900volts to accelera te the electron beam toward the CRT face. Deflection sensitivity and hence calibration depend uponthat voltage, so it is regulated by a stringof l80-volt Zener diodes. Vertical andhorizontal pos ition and sweep time depend upon the 9-volt supplies, so theyare transistor-regulated. The + ISO-voltsupply serves only differential amplifiers, and thei r inherent common-moderejection makes regulation of that supply unnecessary. We shall now proceedto a detailed description of each functional bloc k.
Vertical atte nuator: Voltage dividersRA and RB (Fig. 2) reduce the inputsignal to a maximum of 0.32 volt (8 divi-
FIG. 2.-THE ATTENUATORS. Component s for the verti cal attenuator are mounted on a specia lcircuit board. Also shown in the diagram of the option al mult iplier probe.
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PARTS LIST (Attenuators, Fig. 2)Resistors 1% to lerance or better, 1f2 wattR401-806,OOOohmsR402-162,000 ohmsR403, R412-40,200 ohmsR404, R408, R40&-1 megohmR405--604,OOOohmsR406-909,OOOohmsR407-953,OOOohmsR410-402,000 ohmsR411-1 00,OOOohmsR413-10,OOOohmsR414-4,020 ohm sR415*-9 mego hmsCapacitorsC401- .05)JF, 600 volts, ceramicC402-100 pF, MylarC403, C405-C414, C416*-6-60 pF
togg le switch (Alco MST205T)S402-3-po le, 6-position rotary wafer
sw itchR403-2-po le, 6-posit ion rotary wafer
switc hMiscellaneous: printed circuit board*Note: Components required for optional
x 10 probe
sions at 0.04 volt-per-division) or a minimum of 0.0 I volt (I division at 0.01 voltper-division) . Capacitors CA and CBswamp out stray capacitances to keepthe reactive division ratio exactly equa lto the resistive division ratio at high frequencies . AI--4-10 step-sequence permits coverage of the 10-mV to 10-voltper-division range with two poles of astandard six-position switch .
Vertical amplifier: The overall gain ofthe vertical amplifier (Fig. 3) is about2000 in the full-gain (-;-4) position , andabout 500 in the calibrated (x I) positionof the vertical variable control. ResistorR20 I and D20I provide input protectionin the event of accidental overload.Source-follower Q201 and common-baseamplifier Q202 form a trigger amplifierwith a non-inverting AC gain ofabout 40and a high input impedance.
Transistors Q203and Q204are switchedon alternately by the zero-baseline flipflop (Q307 and Q308, Fig. 4), connecting the base of source-follower Q205alternately to the signal input and toground. The stray capacitance of theseFET's amounts to about 10pF, and produces switching transients of about 10~S duration on the I-megohm input line.
TOP VIEW ·of the sco pe. The ampli fier board isbeneath the CRT. The power-sup ply board is atthe rear near the transformers mounted on theback pane l. The sweep board is up front near theco ntrols. The att enu ato r board, with its five trimmers, is on a bracket held by the vertical-sensit ivity control. Astigmatism control is on rearpanel near base of the CRT.
The switching frequency must thereforebe held below a few hundred hertz toprevent those trans ients from being frequent enough to be seen on the CRTdisp lay .
Transistors Q206 and Q207 are wiredas a variable-gain differential amplifier.Potentiometer R213 is the IO-mV calibrator and sets the gain to four times theindicated vertical sensitivity with R214
+9V +9V +9V +150V0201
0MPF4393 C202 0202R204
10O"F3.3K TO
G S 2N4400 S403-0 INT+1 TRIG R219
R202 10K2 .7K
R2112W
C201270n
R2121200pF 560n
VERTICALINPUTFROMATTENUATOR R201(FIG. 2) 330K
R221 R2220201 33n IK
IN914
R20533K
R207 -9V C203B 27K -9V B20
FROM R206 R217 pFSWEEP 33K R215 470nBOARD 470n(FIG. 4)
HORIZONTAL R225 MPF4393330K 0 R231INPUT G 2.2K(FROM JFIG.2) S HOR DENOTES OFF
0202 R226 POS R232 PC BOARDIN914 2K 5K
HOR
C20G CAL R233
I·I"F 4.7K-9V
-9V
PARTS LIST (Amplifiers, Fig. 3)
FIG. 3-SCHEMATIC DIAGRAMS of the verti cal and horizontal deflection amplifiers. The latt er iscomparatively simple because its response is limi ted to the sweep frequencies.
at minimum resistance. Pot R216 is the40-mV calibrator. It adjusts the indicated sensitivity with R214 at maximumresi stance. Pot R218 is the DC balancecontrol; it sets zero voltage between thetwo emitters at zero input in order thatthe gain control will not shift the verticalposition.
second stage of amplification, producing a maximum differential output ofabout 180volts P-P. Capacitor C203 lowers the impedance between the emittersto track the decrease in impedance between the collectors caused by CRTplate capacitance at high frequencies.Since gain is essentially the ratio ofthose impedances, C203 tends to preserve
or similar N-channel FET (Motorola)0202-2N4402 or similar0206, 0207-2N4400 or similar0208,0209,021 1, 0212-2N3440 or
similar 'Miscellaneous: PC or perforated circuit
boa rd, hookup wire, mountinghardware , trans istor sockets, etc.
ZERO-BASELINE DISPLAY permits reading theDC component of this waveform. Scale factor is1 VIdiv and the sinewave is 3 volts peak-to -peakrid ing on a 4-volt DC level.
a constant gain as frequency increases.Because an 820-pF trimmer would belarge and unstable , we adjust the associated resistor (R202) to suit the capacitor,instead of vice-versa . Capacitor C203thus determines the stage gain , andshould be altered if necessary to produce a stage gain of about 50.
Horizontal amplifier: This amplifier(Fig. 3) is similar to the vertical amplifierexcept that the low-voltage differentialstage is omitted and the entire gain(about 70) is achieved in the high-voltagestage . The differential output voltage required is about 250 volts P-P becausethe second (less sensitive) set of CRTdeflection plates is used. Bandwidth isabout 500 kHz.
electrolytic*Note: selectto keep ratios within ± 1%
**Note: In prototype, C314 was made byconnecting a 47-pF disc in parallel with a6-60-pF ceramic trimmersemiconductorsD301-D308-1N914 or similar silicon
diodeIC301-555 timerIC302-LM318 op-arnp (National)0301 , 0305--MPF4393 or similar
N-channel FET (Motorola)0302,0303,0307, 0308-2N4400 or
similar0304-2N4402 or similar0306-2N4871 or similar uni junction
transistorS401. S403--see attenuator parts listS301-3-pole. t t-posltlon rotary wafer
switch (Centralab PA-10009 or equal)S302-2-pole. 4-position rotary switchMiscellaneous: PC or perforated circuit
boa rd, shielded cable, transistor and ICsockets, mounting hardwa re, knobs.etc .
FIG. 5-THE POWER SUPPLY is simple and inexpensive to bu ild . The voltage-trip ler repla ces theexpensive and dangerous high-voltage pow er transfo rmer used in many scopes. The string of Zenerdiodes replaces a high-res istance voltage-divider string.
»\l:Dr....<0cea
tive pulses from C307. In the AUTO
mode , AC detectors D302, D303, andC306 furnish the positive supp ly as longas the Schmitt trigger is switching. However, if the trigger remains inope rativefor longer than about 150rns, C306 discharges and R316 pulls the trigger inputlow, resulting in automatic triggeringwith no input signal.
Sweep circuit: Transi stor Q304 is a variable-current source that charges the selected timing capacitor (C31O throughC3 14) at a linear rate depending on thesweep variable control and the selectedtimin g resistor (R320 through R322). Pin7 of the NE555 automatically disc hargesthe cap acitor whenever pin 6 rises to +6volts. A so urce-followe r Q305 buffersthe ramp since any current drawn fromit would des troy its linearit y. Pot R325redu ces the ramp to 4.4 volts, thus providin g II divisions of sweep to the 0.4vo lt-pe r-division horizontal amplifier.
continued on page 80
SWEEP LINEAR ITY is evident in this photo of aSOO-kHz triangle waveform at t mY/div.
output (inverted or non-in verted) arecoupled through switch S302-a capacitor and C307 to the trigger input of theNE555, IC 301; that is where the negative edges are used to initiate thesweep ramps.
In the DRI V EN mode , the trigger inputis held high by the + 9-volt supply throughR314 and triggering occurs only by nega-
e lect rolyticC109, C11l-Q.1 uF ce ramic discV1-CRT, 3RP2 was used in prototype.
3EP1 ,3RP1,3BP1 and3ACP11 can beused . See text.
semiconductors0 101-0106,0114-1N4007
Trigger circuits: Source-follower Q30 I(Fig . 4) provides the high input impedance required du ring ex ternal triggering, and the low driving impedance necessa ry for good sensitivity of the Schmitttrigger, Q302 and Q303. The trigger willoperat e with 0.1 volt Pop input , and trigger up to 5 MH z with 0.3-volt Pop input. Th e edges of the Schmitt-trigger
43
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OSCILLOSCOPEcontinuedfrom page 43
The LM318 op-amp (lC302) is used asa voltage comparator, holding the trigger input of the 555 positive until thetiming capacitor has completely discharged. Premature triggering during retrace is thus prevented. The 555 provides a squarewave output at pin 3 thatgoes to +9 volts while the ramp is risingand drops to ground during retrace andhold-off. That line is capac itivelycoupled to the CRT grid to suppress thebeam except during the sweep.
Baseline generator: The retrace-suppression line is used via R330 to synchronize the zero-baseline oscillatorQ306, insuring that the switch frombaseline to signal display will always occur at the start of a retrace when thebeam is suppressed. For the lower sweepspeeds, synchronization requires aslower oscillator, and for that C319 isswitched in.
Each time unijunction transistor Q306fires, C316 discharges through R332,setting flip-flop Q307-Q308 throughD308 and initiating a baseline sweep.After the baseline sweep (or severalsweeps if C316 is not discharged afterthe first one) pin 3 of the 555 goes low,bringing the base of Q307 low throughC315 and D307, thus resetting the flipflop for a series of signal displays .
Power supplies: The power supp lies(Fig. 5) are entirely conventional exceptfor the - 900-volt tripler. Diodes D 105and D 106charge C 102 to the peak negative voltage of the transformer secon dary on the negative half cycle. On thepositive half-cycle, C 102 and the secondary appear in series to charge C 10Ito twice the peak secondary voltage(negative on top), through DI03 andD 104. On the next negative half-cycle ,C 101 and the secondary appear in seriesto charge C 103 to three timesthe peaksecondary voltage through D10I andD102. The drain on that supply is about200 uA , so the 0.1 /-IF Mylar filters arequite adequate. Some of those capacitors are used at 20% or so above theirrated voltage , but many have been tested at four times rated voltage with nobreakdowns. Any string of five to tenZener diodes adding up to about 900volts will do for DI09 through DI13 if180-volt Zener diodes are hard to find.Capacitor C 105 filters out the 6O-Hznoise picked up from the power trans former by the CRT heater winding.
We must breakoff our discussion ofthe oscilloscope's power supplies nowand will conclude it next month whenwe will also go into construction,checkout and calibration, R-E
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80
TRIGGEREDOSCILLOSCOPE
Part II-Construction details and calibration instructions for thelow-cost scope that features a continuously displayed zero baseline.
DANIEL METZGER and DENNIS PERRY
TOP VIEW of the scope. The amplifier board is beneath the CRT. The power-supply board is at therear near the transformers mounted on the back panel. The sweep board is up front near the controls.The atlenuator board, with its five trimmers, is on a bracket held by the vertical-sensitivity control.Astigmatism control is on rear panel near base of the CRT.
LAST MONTH WE DESCRIBED THE FEAtures of this inexpensive DC scope andwent into detail on the operation of itsvarious circuits . We continue thismonth by resum ing our broken-off discussion with suggestions on selectingthe CRT to meet your requirements.
ConstructionMan y types of CRT' s have been used
in this design , including 3BP l, 3EP I,3ACPII, 3FP7 , 3RPl, and 2AP I. Fiveinch type s can be used , but whatever isgained in screen size will be lost insharpness of focu s. The 3RP IA and3WPI are especially nice because theyare flat-faced. The 3WPI has about twicethe deflection sensitivity of the others,and can be used to produ ce a scope with5-mV sensitivity. The CRT must be shielded with MuMetaI (nothing else willwork) unless the power transformerscan be located two feet from the CRT.Surplus houses that sell CRT's usuallyhave fully formed shields.
DISPLAY of a SOo-kHzsquarewave at 0.4 JlVIdlvshows a fast rlsetlme and clean squarewave response.
The vertical and horizontal outputwires must run straight to the CRT andbe kept away from eac h othe r and fromot her wiring and the chass is. The vert ica l and horizont al inputs should be keptshort and separa te from other wire bundles. The wires to and from the TRIGGERLEVEL switch carry fast squarewaves
and must be shielded to prevent coupling to other wires . The wires to theVERTICAL VARIABLE GAIN control shouldbe kept reasonably short. Other wiringshould be bundled and laced in the in- 5:terests of neatness. ?<
The input attenuator and sweep-tim- <0
ing resistors must be held to 1% if good ~
53
•
•
o
o
...J ...JIII III 0
TO B-L ONAMPL BOARD~
TO •ARMS OF S401-bAND S304-c
TOR317
TO ARM ,--..,S301 -b t
TO ARMS301-0
TO
........l..- .._ ..--..-----.. j;
o
o
•
•
FIG. 8-THE SWEEP-GENERATOR PC-board foil pattern. The pads along the top edge are forconnections to off-the-board components and leads to other circuit boards.
FIG. 9-HOW THE COMPONENTS ARE PLACED on the sweep-generator PC board. Note the positions of the three jumpers.
FIG. 6-FOIL PATTERN for the attenuator usedin the vertical-sweep circuit.
FIVE 6-60pF TRIMMERS(C 405 - C409)
GND
TOS402b
r-1-1/81~
COPPERSIDE
S402-0
FIG. 7-COMPONENT PLACEMENT GUIDE forthe vertical-input attenuator. The precision resistors are on one side and the frequency-eompen sating capacitors are on the other.
NOTE: CONNECTION TO HORIZONTAL DEFLECTION PLATE SHOULD BE MADESO THAT BEAM SWEEPS FROM LEFT TO LIGHT ; VERTICAL DEFLECTION PLATESSHOULD BE CONNECTED SO THAT POSITIVE INPUT TO VERTICAL AMPLIFIERPRODUCES UPWARD DEFLECTION OF BEAM .
FIG. 11-THE DEFLECTION-AMPLIFIER board has three jumpers and six trimmers for circuit calibration and adjustments. Leads to CRT deflection plates should be as short as practical to minimizestray capacitance.
s::>-<coceo
55
Vertical: 50mV P-P, 1kHz sineware input ;R214 at min resistance, S401 at OC
Horizontal: 2V P-P, 1kHz sineware to EXTHOR, S403 at OAV/OIV
0302C0303C + 1 to +9 SOR 0302,0303C306 + 8 10 D302,030303048 +7.3 to+8.5 Varied by R317R320-R322 + 1.5 DC across RT AT CALIC301pin 6 o to '+6RAMP 03040305S . L 1 to +7 0305
RAMPIC302Din 6 + 9 to -9 SOR IC302, R327IC301nin 3 o to + 9 S0 R IC3010306E o to 7 RC Charge; 0306, R278030681 + 5 SPI,KE . 0306Q307C0308C o to + 9 S0 R 0307,0308
FIG. 1o-PRINTED-CIRCUIT FOIL PATIERN forthe board for the horizontal and vertical deflection elrcults,
MD3POWER SUPPLIES
D.PERRY5/78
j ....J
..
0 ~\\\\\\FOC tN T tXfT CT +9
FIG. 12-THIS PRINTED-CIRCUIT PATTERNsimplifies construction of the power supply.
FIG. 13-POWER-SUPPLY COMPONENT LAYOUT is simple. Be careful; some of its voltages aredangerous.
CalibrationVertical: First display a 2oo-kHz
squarewave and adjust high-frequencycompensation control R222 for sharpestcorners with no overshoot. With rangeS402 at 1 V/div and variable R214 atmaximum resistance, inject a 2.12 voltRMS (6.0 volts p oP) loo-Hz sinewave,and adjust R216for a six-divisiondisplay.Now change the range to 4 V/div and,with variable R214at minimumresistance(74), adjust R213 for a six-division display. With the input grounded, adjustR218 so the trace remains stationary asR214 is rotated. The final step is to displaya I-kHz squarewave, and on eachof the ranges from 0.1 to 10V/div adjustthe corresponding trimmer capacitorfor the best squarewave with no rounding or overshoot.
Horizontal: With the horizontal atten continued 01/ page 110
boards. The foil patterns for the attenu ator, sweep circuits, deflection amplifiers, and power-supply PC boards are inFigs. 6, 8, 10, and 12, respectively. Thecomponent layouts for those circuitboards are in Figs. 7,9, II,and 13.
Initial checkoutA spot can be focussed on the screen
with only the power-supply board andCRT circuitry wired in. The 9-volt supplies will each need a temporary 470ohm load if they are to be tested at thispoint. Now disconnect the primary ofT 10I to disable the high-voltage supplies while the sweep and low-level amplifiers are tested. The troubleshootingchart (Table I) shows the voltages to beexpected at various test points. Oncethe Schmitt trigger, sweep generator,baseline generator, and low-level ampsare determined to be functioning, thehigh voltage can be reconnected.
BI ,
E~B22N4871
( MOTOROLA)
3 TO 4CRT
E~B' .- "\+"" ,
C2N3440
( MOTOROLA)
0101 0102 ~ 0103~ ----.- T---CIOI--
---CI03 - - -
0105 0106--.+-- ----.I-
to be used, the fixed frequency-compensating capacitors (CB) must be held to5% tolerance.
LEADS CAN BE MPF4393FORMED TO A ( MOTOROLA)TO-5 PINCON FIGURATION
0400- 80410(GE l
PHYSICAL OUTLINES AND PINOUTSfor the discrete devices used In the scope as active circuits. Beespecially careful with the installation of the look-alike plastic devices.
calibration accuracy is expected. Thetiming capacitors must at least be in thesame ratio, so if one is 7% high, strive tomake them all 7% high. If a x 10probe is
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6is-ccr:
56
BUILD AMASTERPIECE OF SOUND
----------------------_--1
Enc losed is $6.00 for my Demo-Package (LP wit h104-page color cata log .) \
OSCILLOSCOPEcontinued from page 56
WARC-'79continued fro m page 109
fixed and broadcast satellites that willbe able to operate in the 12 GHz portion of the spectrum in the westernhemisphere.
The 11.7- to 12.I-GHz band will beall ocated to the Fi xed Satellite Service(space-to-earth) shared w ith other serv ices; the 12.0- to 12.7-GHz band willbe allocated to broadcasting and broadcasing satellites, shared with other services . The specific frequencies to beassigned to the broadcasting satell iteservice will be allocated at a Conferencescheduled to be held in 1983. That willbe followed by a general satell i te conference as mentioned above.
The oveniding issue of the 80's willbe the movement on the part of developing countries to plan the assignment and use of orbital slots and frequencies in such a way as to assure allcountries an equal "sli ce of the pie."WARC-79 did not address that issuecompletely, but only deferred it to subsequent space conferences which willbe held in th is decade. Major batt les onthe issue of equal right s may loomahead. R-E
Wersi Organs & KitsDept. 2114104 E. Firestone Blvd.Santa Fe Springs. CA 90670
CDWER51Wers i Elect ronics. Inc.Dept. 211720 Hempstead RoadLancaster . PA 17601
Name _
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percussion and sustain. 'lVersis famousstring orchestra and bass guitar. Exclusive Sound Computer for 32-128 "One
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