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CMC250 Servlcb

LIST OF TABLES

Table Page

1-1 GeneralCharacteristics ................................................................... 1-2
1-2 Electrical Characteristics .................................................................. 1-3

4-1 Test Equipment Required .................................................................. 4-1

6-1 Relative Susceptibility to Static-Discharge Damage ............................................6-1
6-2 ExternallnspectionCheckli ...............................................................6-3
st
6-3 InternallnspectionChecklist ............................................................... 6-3
6-4 NormalCMC250Displays ................................................................. 6-8
6-5 CH 1 Analog Circuit Waveforms ........................................................... 6-10
6-6 GATETimeLogicCheck ................................................................. 6-10
6-7 FUNCtionLogicCheck .................................................................. 6-11
6-8 MaintenanceAids ....................................................................... 6-13
-
Section 1 CMCPSO Sewice
. .

GENERAL INFORMATION

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SPECIFICATION
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General lnformatloa~CMC250
Service

Table 1-2
Eiectrlcal Characteristics

Characteristics I Performance Requirements
-
Lilne Voltage Range
- 1 90 to 110,108 to 132,198 to 242, and 216 to 250 Vac at 50-60
I
Hz.
Power Consum~tion 1I 15 VA, 12 w maximum.
FREQUENCY
Frequency Range
Channel 1 5 Hz to 100 MHz sine wave. . ,
Channel 2 80 MHz to 1.3 GHz sine wave.
Accuracy Time base accuracy + 1 count.
Resolution (selectable)
Channel 1
kHz Mode
...
. 0.1 Hz to 100 Hz.
MHz Mode 1 Hz to 1000 Hz.
Channel 2 10 Hz to 10 kHz.
PERIOD
Range 1 0.4 ps to 0.2 s.
~requency~ange 5 Hz to 2.5 MHz sine wave.
Accuracy & 1 count + time base error + trigger err0r.a
Resolution (selectable) 100 ps to 100 ns.
TOTALIZE
Range I 0 to 99,999,999 counts plus overrange.
Repetition Rate 1 5 Hz to 10 MHz sine wave.
CHANNEL 1 INPUT
Bandwidth 15 Hz to 100 MHz, AC coupled.
Maximum lnput Voltage
I 42 Peak-
Sensitivity (minimum input voltage)
5 Hz to 30 MHz
1 20 mvrms.
r 30 MHz to 100 MHz 50 mVrms.
CHANNEL 2 INPUT
Bandwidth 80 MHz to 1.3 GHz, AC coupled.
Maximum Input Voltage
A 1 Vrms.

Sensitivity (minimuminput voltage)
80 MHz to 600 MHz 10 mVrms.
600 MHz to 900 MHz 25 mVrms.
900 MHz to 1.3 GHz 50 mVrms.
Trigger error is typically f 0.3 of reading divided by the number of cycles averaged, for input signals greater than 100 mV
with SIN ratio better than 40 dB.
Section 3.- CMC250 Service

THEORY OF OPERATION

digit strobes are fed back to these control inputs via the
front panel switches. The control inputs set operating
This section contains a description of the CMC250 conditions according to which strobes are applied.
1.3 GHz Frequency Counter circuitry. General operation The time base Is a 10 MHz oscillator for Channel 1
of the instrument is described in the Black Diagram
rne%wremnts and a 3.90625 MHz oscillator for Chan-
Description. Eachfunctional,,circultis described in more
nel 2 mmwrements.
detail in the Detailed Circuit on.
The pmm supply provides regulated dc voltages. The
The schematic diagram afid the Main circuit board power wpply drcuit can be set with the LINE VOLTAGE
illustration are located in tW ~ i g section s this
! ~ of SELECT switches as needed to accommodate various
manual. T understa
o line voltages.
sectidn, refer to both
this section, and to the schemsvtlc &%ram.
DETAILED ClRCUlT DESCRIPTION

DIGITAL LOGIC C ~ N V O N S Channel 1 Input Cirsuh
Functions and operatian of d bgfccircuits are r e p
m Slgnala waRh t3wq~mmies l o w 106 MHz are connected
b
resented by logic q b @@l
mw tmnlnology. Must ; to the Ch-11 Input Circuit vla the CHANNEL 1 NPUT
logic runctions m p o s ~ ~ o cormector on front panel. The lnput signal Is capacl-
e ~ ~ c
convention. Po crf notationwhere- tiwly aoupkivd via C to the divider of R2 and F . When
l B
bythe more positiveof twg l l &dmTY1UE(or1) state;
ws the INPUT VOLTAGE Wrch SB is set to !UnV-W(LO),
the more negative level I state. In thts the full voltage a ~ t m dMder goes to th$ Inpu!
tailis
manual, the TRUE state Igh, and the Buffer; when St? is set ts, 1V-42V(Hl), the shgrd i s cak
FALSE Mate as low. The voM@@S t eonstTtut8 a high or
W n a f through an Attenuator circuit before g.aIng to the
a low state vary between speclflc devices. For device Input ~I.@BY.
cfiaracterlstia, refer to the muS-wys data book.
ATTENUATOR. Voltage Wider R2 arid R3 attenuates
Channel 1 Input signals by a factor of 10when the INPUT
BLOCK DIAGRAM DESCRIPTKIN VOLTAGIE switch S8 is set to HI.
INPUT BUFFER. Eitherthe entire signal (S6 set to LO) or
Signal input to Cheu7nsl 1 is through the CHANNEL 1 the attenuated signal(S6 set to HI) Is appliedto the Input
INPUT wrmector on t efront panel. Channel 1 is for fre-
h Buffer. The Input Buffer isolates the signal being tested
qmm3es below 100MHz and has a s4gn~l-conditioning m m the circuitry inftle frequency counter. This voltage is
feature. The elttenuator wltcfi Sf$gaslect$ either full volt- level-clmped'to a m m m
iu
a
x of 0.6 volts by transistors
age when INPUT VDUABE is set to LO, or passes the Q1 &mi Qa and then applSed to the high-impedance
signalthrough a 1OX atttmuatwwtwnINPUTVOLTAGEis buffer stage. This consists af FET Q3 whlch provides
set to Hi. gsod smsitiivityoverthe Channel 1frequency range and
Q4 which s v e s as a w e n t s o m for successive
Slgnaj input to CharWeel 2 is through the CHANNEL 2 stages.
INPUT connector on front panel. Channel 2 is for
frequencies from 80 MHz to 1.3 GHz, and the Channel 2 LOW PASS FILTER. The Low Pass Filter removes the
Input circuit includes a divide-by-256 feature. high-frequency components (noise) from a signal, so
that lower frequencies can be accurately counted. When
The main counter, integrated circuit U16, performs all t h e m PASS FILTER switch 57 is ON, D l and D2 are
frequency, perlod, and totalization functions and drive8 biased on, providing an ac path to ground thrbugh Dl,
the displays. Four control inputs on U16 determine and the filter action of R9 and C9 is enabled. When the
operating mode, resolution, time base frequency, and switch is OFF, D l and I32 are off, isolating C9 from
decimal point placement. Selected time-multiplexed ground and disabling the filter actlon.
FILTER

KHz, MHz
SELECT
CHANNEL INPUT AMPLIFIERI
INPUT BUFFER

u--l
ATTENUATOR
TRIGGER
+lO

I
CHANNEL 2 AMPLIFIER/
INPUT +256
.
FUNCTION1

,
RANGE
CONTROL
LOGIC

1 FEEDBACK

?J
ALL OTHER
CIRCUITS

AC POWER
INPUT
TRANSFORMER - I

t5V
REGULATOR
v~
I

DIGIT
STROBES
L
A
- ---. -t

- t

-
Theory of Operatlon CMC250 Service

AMPLlFlER/SCHMlTTTRIGGER. This circuit amplifies Channel llChannel2 Select
and shapes the Channel 1 signals into square waves
suitable for use in the digital circuits in the CMC250. It The combined action of U13, U19, and Ul, which is con-
consists of three-stage ECLampllller IC1, transistors Q5 trolled by the front-panel FUNCtion switches, provides
and Q6 (used as ECL-to-TTL level shiners), and U16with an input signal wlthin its frequency limits. In Fre-
associated components. The waveform obtained quency MHz mode, the Channel 1 signal i divided by
s
across R25 is a 0 to 2.8 volt square wave with polarity ten in U14 and applied. In Frequency Channel 2 mode,
opposite that of the Channel 1 input signal. the signal from the Channel 2 input is divided by 256 in
IC4 and applied. In Frequency kHz, PERIOD, and
TOTALize modes, the Channel 1 signal is applied with no
Channel 2 Input Circuit frequency division.

The Channel 2 lnput circuit consists of integrated clrcuit Channel 1 Signal Gating (TOTALize mode)
IC4, diodes D8 and D9, and associated components.
Channel 2 input slgnals are divided by 256 before going InTOTAUze mode, inputs to U19 on pins 5 and 6 control
to transistors Q7 and Q8 (used as ECL-to-TTL level the olutput on pin 18. U1D pin 11 is connected to U19
shifters). The Q7 output goes to the next stage, Channel pin 5; U2 pin 10 is high in TOTALize mode and is con-
1lChannel2 Select. nectedto U19 pin 6. The undivided signal from U13 pin 3
is gated additionally by the signals at U1D pins 12 and
13. U1D pin 12 is controlled by HOLD switch S2viaflip-
Channel 1 kHz/MHz Select flop U1A and U1B. U l D pin 13 is connected via RlO5 to
the rear panel TOTALize STARTISTOP INPUT. The
The Channel 1TTL-level output Is appliedto the Channel
undivided signal from U13 pin 3 can thus be gated
1 kHz/MHz Select circuit, comisting of U13, U19, U1, manually by S2 or electronically by a signal applied to
U4, and associated components. U13B input pins 4 and the rear-panel INPUT. When no signal is connected to
5 go low whenever U4B pins 4 and 5 are low; so that the TOTALize STARTISTOP INPUT, the input jack is
whenever the kHz mode is selected, the kHz signal is pulled high by R103.
gated through to U13D. At all other times, the MHz
(divided by 10) signal from U14 is gated through U13C. FunctioniRange Control Logic
U13C pin 9 goes high when U2 pin 2 is high.
U3C and U3D provide contact switch debounce for the
Divide-by-Ten. The Channel 1 output of U13 pin 3 goes FUNCtion switch S3. Their output clocks U2, a decade
to U14 and U13 pin 12. U14 is a decade ripple counter counter that selects the operating FUNCtion.
which functions as a divide-by-tm. Voltage levels on
U13 pins 4-1 3 and U19 pins 2 and 19 select either the U3A and U3B debounce GATE switch S4. The output
decade-divided signal from U14 pin 2 or the undivided triggers U6, a decade counter that selects the operating
signal from U13 pin 3. This selection is governed by two time base (GATE time).
lines: one from U4B pin 6, which is high only during
Frequency MHz mode; and one from U2 pin 2, which Counter Circuit (U16)
goes high whenever Frequency MHz mode is selected.
The Frequency kHz or MHz selection autput (from U19 IC U16 is the main counter for the instrument. It performs
pin 18) is governed by two lines: one from U1D pin 11, all frequency, period, and totalize functions and drives
which is low in all modes except TOTALize, and one from the displays. U16 requires an input signal of CMOS
U2 pin 4, which goes high whenever Channel 2 mode is digital logic levels, a time base, and connections for
selected. feedback of display digit strobes.
A A A A A A A A
41

$ k $ PIn S 2 2 6

4
g
I-z
z- JI J
0
0

S
3 t-
o
8
3
$!
-
Theory of Operation CMC250 Service

Time Base The kHz/p indicator D25 is connectedviaU4 pin 3 tothe
Frequency kHz, PERIOD, and CHECK selected. The in-
The Channel 1 and Channel 2 time base signals are dicator lights when any of these modes are selected.
provided by two separate crystal oscillators. The 10 MHz
crystal oscillator for Channel 1 (Y2) is connected to the The GATE (count) indicator D26 is connected via U7F to
oscillator input of U16 pin 35 from U17A, which buffers U16 pin 3. This pin goes low whenever a measurement is
the crystal oscillator output to a level suitable for driving in progress. The kHz, MHz, CH 2, PERIOD, TOTAL, and
U16. The 3.90625 MHz crystal oscillator for Channel 2 CHECK indicators LED1-LED6 are connected via U5,
(Y1) is connected to the UCT OSC IN input (pin 33) of
which buffers the output of U2. The GATE (time base)
U16. The 3.90625 MHz crystal oscillator is required to indicators are driven by U7, which is connected to the
offset the effect of prescaling the input (by 256) in the
sequential outputs of U6.
Channel 2 input circuit.

HOLD Switch Power Supply
The HOLD switch S2 is conmcted to U16 and U1 pins
11-13 and Ul9 pins 5 and 6, via U1 pins 1-6. U1A and The transformer is a universal type whose primary
U1B provide switch debaunw and act as a flip-flop to windings may be selected for various line voltages by
lock the output of U1B high or low. the rear panel LINEVOLTAGE SELECT switches, S8 and
S9.
LED Indicators
The output of the secondary side is rectified by D l 10,
The MHz indkator D24 is connected to the output of U4 D l 11, D l 13, and D l 14 and filtered by C120 and C124.
pin 6. This output goes high when Frequency MHz or Regulators Q9 and Q10 provide regulated +5 volts for
Channel 2 is selected. the instrument.
Section 4 -CMC250 Service

PERFORMANCE CHECK PROCEDURE

INTRODUCTION used infrequently. If these checks indicate a need for
readjustment or repair, refer the instrument to a qualified
This procedure checks many of the electrical character- sewice person.
istics listed in Table 1-2 in Section 1of this manual. If the
instrument fails to meet the requirements given in this
performance check, the adjustment procedure in
Section 5 should be done. This performancecheck may TEST EQUIPMENT NEEDED
also be used as an acceptance test or as a trouble-
shooting aid.
The test equipment listed in Table 4-1 is a complete list
You do not have to remove the instrumentcase to do this of the equipmentneededfor this performancecheck and
procedure. All checks can be made using the controls the adjustment procedure in Section 5. All test equip
and connectors accessible from the outside of the ment is assumed to be operating within tolerance.
frequency counter. Detailed operating instructions for test equipment are
not given in this procedure. If operating information is
T ensure instrument accuracy, check its performance
o needed, refer to the appropriate test equipment instruc-
after every 2000 hours of operation, or once each year if tion manual.
PREPARATION now be slower thw it was at the previous
setting.
Ensure that all power switches are off.
g. Set the GATE switch to 2.7~11.0s.
Ensure that all test equipment and the CMC250 are
suitably adapted to the line voltage to be applied. h. CHECK that the display reads 10000.000
(9999.999 to 10008.001) kHz and the GATE
Connect the equipment under test and the test cator is flashing on and off; flashing shoul
equipment to a suitable line voltage source. Turn all be slower man it was at the previous
equipment on and allow at least one hour for the setting.
equipment to warm up and stabilize.
i. Set the GATE switch to 27s/tQs.
Set the CMC250 controls as follows during warm-up
time: j. CHECK that the display rmds 0000.0000
(999.9999 to 0000.0001) kHz and the
INPUT VOLTAGE 5OmV-SV(L0W) RANGE indicator ie lit ( 0 O a 0 or0000.
00.)0
(button out) CHECK that the GATE indicator is flash
LOW PASS FILTER OFF (button out) and off;flashing should now be slower th
was at the previous GATE sefflng.

PROCEDURES gEaTE

Check GATE (resolution) settings and display At this slower GATE @ttlngJ yoo wiN mtice a
uslng CHECK mode delay afteryou mImt ttw 27s/10s WTE setting
and before the &#play changes.
NOTE
2. Check Channel 1 Frequency Range and
No test equipment is required for this general Sensltlvlty
check of instrument operation. In CHECKmode
the input clrcuit is connected internally to the a. Set the CMC250 FUNC switch to kHzllO
time base oscillator. and the GATE s m b 2.W1.a.
w
b. Set fwrctlm generator to 1 kHz.
a. Bet CMC250 FUNC switch to CHECK and set
GATE switch to 0.027s10.01 s. c. Connect a coaxial cable fm the funct
i
generator output thraugh a 10X attwuator
b. CHECK that display reads 10000.0 + 1 (9999.9
a 50 0 termination to the hput of
to 10000.1) kHz and the GATE indicator light is oscilloscope.
flashing on and off.
d. Adjua the funetlon generator output arnplito
c. P mHOLD (button in) and check that the GATE for 150 mV p-p sine wave.
indicator limt remains o f Press HOLD again to
f.
release (butten o t and check that the GATE
u) e. Remove t b connection from the oscil
indicator resumes Washing. and c d it to the CMC250 CHA
INPUT connector.
d. Hold the RESET button in and CHECK that the
display reads .O and the GATE indicator light is f. R e d m the frequency from the function g
off. Release the RESET button and CHECK that ator to 10 H z
the display reads 1W . 0 and GATE indicator
resumes flashing. g. CHECK that the CMCZ50 triggers on 1QHz.
e. Set GATE switch to 0.27s/O.l s. h. Set the CMC250 FUNC switch to MHz/l
f. CHECK that the display reads 10000.00 1 I. Rmovethe coaxial cablefram the fundan
(9999.99 to 1MKK).O1) kHz and the GATE erator and corm& tilt3 slgr?al generatw k,
indimtor is flashing on and off; flashing should ~f.Il'05cope. Set the signal geMerator
Performance Check Procedure-CMC250 Service

50 kHz. Set the signal generator for 150 mV p-p b. Connect a coaxial cable from the signal gener-
output. Disconnect the oscilloscope and con- ator output through a 1OX attenuator and a 50 a
nect the generator to the CMC250 CHANNEL 1 termination to the input of the oscilloscope.
INPUT connector.
c. Set the signal generator to 50 kHz and 150 mV
j. Set the signal generator to 100 MHz. p-p output. Disconnect the oscilloscope and
connect the generator to the CMC250 CHAN-
k. CHECK that the CMC250 will trigger on 150 mV NEL 2 INPUT.
p-p at 100 MHz.
d. Set the signal generator to 100 MHz.
.. Set the signal generator to 1 MHz.
e. CHECK that the CMC250 will trigger on 150 mV
m. Press in the LOW PASS FILTER button on the p-p at 100 MHz.
CMC250.
f. Disconnect the test equipment.
n. CHECK that the CMC250 does not trigger.
4. Check CH 1 and CH 2 Time Base Accuracy
o. Set the LOW PASS FILTER buttonto OFF (button
out) and set the INPUT VOLTAGE button to a. Connect a 10 MHz signal from the frequency
3V-42V(HI) (button in). standard to the CMC250 CHANNEL 1 INPUT
connector. Set input voltage to 150 m .
V
p. Remove the connection from the CMC250 and b. Set CMC250 FUNC switch to kHz/lOMHz and
connect it to the os6~lloscope.
Remove the 1OX
the GATE switch to 27s/lOs.
attenuator and the 50 0 termination.
c. CHECK that CMC250 display reads 10000.W
q. Adjust the signal generator output amplitude for kHz + 2 (9999.998 to 10000.002 kHz).
8.4 V p-p.
d. Disconnect the standard signal from the CHAN-
r. Remove the connection from the oscilloscope NEL 1 INPUT connector.
and connect it to the CMC250 CHANNEL 1
INPUT connector. e. Connect a 100 MHz standard signal the
CHANNEL 2 INPUT connector.
s. CHECK that the CMC250 triggers on 1 MHz.
f. Set CMC250 FUNC switchto CH 2 andthe GATE
t. Disconnectthe test equipment. switch to 27~110s.
3. Check Channel 2 Sensitivity g. CHECK that CMC250 display reads 100.00000
MHz 2 (99.99998 to 100.00002).
a. Set the CMC250 FUNC switch to CH 2 and set
the GATE switch to 2.7~11.0s. h. Disconnect the test equipment.
-
Section 5 CMC250 Service

ADJUSTMENT PROCEDURE
INTRODUCTION c. Set the oscilloscope to 10 mv per division.
There are four callbratlon adjustments-the Channel 1 d. Set the signal generatorto 50 kHz, 56 mV peak-
Sensitivity adjustment, the Channel 1 Totalize Sensitivity to-peak output (5.6 divisions at .I0 mV per
adjustment, and the two Time Base adjustments. T o division).
ensure Instrument accuracy, the Channel 1 Sensitivity
and the Channel 1 Totalize Sensitivity adjustments e. Disconnect the cable from the oscilloscope and
should be done every 2000 hours of operation or at least connect it to the CMC250 CHANNEL 1 INPUT
once each year if used infrequently. Do not attempt to do connector.
the Time Base adjustments unless you have a standard
frequency source with a known accuracy of at least five f. Set the signal generator to 30 MHz and check
parts in ten milllon (0.5 ppm). the CMC250 display for the correct reading. If
reading is correct, go to step h.
PREPARATION FOR ADJUSTMENT g. ADJUST-Variable resistor R10 on the Main
Make the adjustments in this procedure at an ambient circuit board until the CMC250 readout agrees
with the signal generator output reading. Turn
temperature of +2I0C to +2SQC (+70

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