Tektronix CFG253 Manual

CFG253 Performance Verification & Adjustment Procedures
Page 1of 19 Procedure #: CP1005 Revision: A
p Service Procedures
Product: CFG253 3 Mhz Function Generator
Title: Performance Verification & Adjustment
Procedure #: CP1005 Revision: A
Prepared By: Roy Lindley
Measurement Business Service Support
REVISION LEVEL SUMMARY:
Revision # Date Initiator Level Change
From: To:
Description
A5/16/97 Roy Lindley n/a Initial release

CFG253 Performance Verification & Adjustment Procedures
Page 2of 19 Procedure #: CP1005 Revision: A
CFG253 PERFORMANCE VERIFICATION PROCEDURE
CONTENTS:
Preparation 3
Check DC Offset 3
Check Main Output Amplitudes 4
Square Wave Overshoot, Rise/Fall Time 6
Check Square Wave Duty Cycle 7
Sync (TTL) Output 8
Sine Wave Distortion 9
Frequency Dial Accuracy 9
INTRODUCTION
To ensure instrument accuracy, check its performance after every 2000 hours of operation or
once each year if used infrequently.
The instrument case does not have to be removed for the Performance Check procedure. All
necessary controls and connectors are accessible from the outside.
Test Equipment: Requirement: Example:
Test Oscilloscope 5mV-5V/Div, 50nS/Div Tek TDS210
Frequency Counter > 3MHz, < 1 % Tek CMC251
Distortion Analyzer 100KHz AA501A
Coax Cable 50 ohm P/N 012-0057-01
50 Ohm Terminator P/N 011-0049-01

CFG253 Performance Verification & Adjustment Procedures
Page 3of 19 Procedure #: CP1005 Revision: A
PREPARATION
Connect the instrument and test equipment to an appropriate power source and allow 20
minutes for warm up and stabilization. Set the controls as listed below during warm up.
Initial CFG253 Set-Up:
AMPLITUDE Mid Range
DC OFFSET Pushed In
SYMMETRY Midrange Detent
RANGE 1K
FUNCTION All Buttons Out
VOLTS OUT Button Out
FREQ/10 Button Out
SWEEP Button Out
SWEEP RATE Midrange
SWEEP WIDTH Midrange
FREQ DIAL 0.3
1. CHECK DC Offset
a. Pull out the DC OFFSET knob.
b. Test Scope Set-Up:
Volts/Div 2V
Time/Div 0.2 mSec
c. Connect MAIN OUTPUT to test scope vertical input via coax cable and 50 ohm
terminator.
d. Set test scope Vert Coupling to GROUND, center the trace, then set Coupling
back to DC.
e. While turning the DC OFFSET knob from CCW to CW and back, check for for >
+5 V with DC OFFSET knob CW and > -5 V with the knob CCW (+/- 2.5 Div on
test scope).
f. Push the DC OFFSET knob in (off).

CFG253 Performance Verification & Adjustment Procedures
Page 4of 19 Procedure #: CP1005 Revision: A
2. CHECK MAIN OUTPUT AMPLITUDES
a. Set-Up:
AMPLITUDE CW
DC OFFSET Pushed In
RANGE 1K
FUNCTION Triangle
VOLTS OUT Button Out
FREQ/10 Button Out
FREQ DIAL 3.0
b. Test Scope Set-Up:
Volts/Div 2V
Time/Div 0.2 mSec
c. Connect MAIN OUTPUT to test scope vertical input via coax cable and 50 ohm
terminator.
d. Check the test scope display for > 5 divisions (10V).
e. Rotate the AMPLITUDE knob to nearly CCW.
f. Set test scope to 10 mV/Div. Check that the display reduces to less than 5
divisions (50mV) as the AMPLITUDE knob approaches the CCW stop.
g. Set the VOLTS OUT button in and change the test scope Volts/Div to 5mV.
h. Check for a display of < 1 division (5mV) as the knob approaches the CCW stop.
i. Set the test scope Volts/Div to 0.2 V. Rotate the AMPLITUDE knob fully CW.
j. Check the display for > 5 divisions (1V).
k. Return the VOLTS OUT button to the out position and ensure that the
AMPLITUDE is CW.

CFG253 Performance Verification & Adjustment Procedures
Page 5of 19 Procedure #: CP1005 Revision: A
l. Set the FUNCTION to Square Wave. Use the CFG253 and test scope settings in
Table 1 to check the MAIN OUTPUT AMPLITUDE for the indicated settings :
TABLE 1
Function Range Volts Out
button
Freq.
Dial
Test Scope
Volts/Div
Test Scope
Display
Square Wave 1K Out 3.0 2V/Div > 5 Div
Sine Wave 1K Out 3.0 2V/Div > 5 Div
Sine Wave 1K Out 0.3 2V/Div > 5 Div
Square Wave 1K Out 0.3 2V/Div > 5 Div
Triangle 1K Out 0.3 2V/Div > 5 Div
m. Remove the 50 ohm terminator and connect the coax cable directly to the test
scope input.
n. Set the test scope Time/Div to 1uSec.
o. Check the test scope display for each setting in Table 2:
TABLE 2
Function Range Volts
Out
Freq.
Dial
Volts/D
iv
Display
Triangle 1M Out 3.0 5V/Div > 4 Div
SquareWave 1M Out 3.0 5V/Div > 4 Div
Sine Wave 1M Out 3.0 5V/Div > 4 Div
p. Press the VOLTS OUT button in. Check the test scope display for the settings in
Table 3:
TABLE 3
Function Range Volts
Out
Freq.
Dial
Volts/Div Display
Sine Wave 1M In 3.0 0.5V/Div > 4 Div
Square Wave 1M In 3.0 0.5V/Div > 4 Div
Triangle 1M In 3.0 0.5V/Div > 4 Div

CFG253 Performance Verification & Adjustment Procedures
Page 6of 19 Procedure #: CP1005 Revision: A
q. Rotate the AMPLITUDE knob nearly CCW.
r. Set the test scope Volts/Div to 5mV.
s. Check the display for < 2 divisions (10mV) as the knob nears the CCW stop.
3. Square Wave Rise Time and Fall Time
a. Test Scope Set-Up:
Volts/Div 5V
Time/Div 0.5 uSec
Trig Slope +
b. Set-Up:
AMPLITUDE CW
DC OFFSET Pushed In
RANGE 100K
FUNCTION Square Wave
VOLTS OUT Button Out
FREQ/10 Button Out
FREQ DIAL 3.0
c. Connect MAIN OUTPUT to test scope vertical input via coax cable WITHOUT
the 50 ohm terminator.
d. Adjust AMPLITUDE knob for a 4 division display on the test scope.
e. Set Time/Div to 50 nSec/Div. Adjust Trig Level control as necessary to display
the rising edge of the Square Wave.
f. Check risetime between the 10% and 90% points for < 100 nSec (2 Div).
g. Set test scope Trig Slope to - (negative). Adjust Trig Level to view the Falling
edge of Square Wave.
h. Check the Fall Time between the 10% and 90% points for < 100 nSec (2 Div).

CFG253 Performance Verification & Adjustment Procedures
Page 7of 19 Procedure #: CP1005 Revision: A
4. Check Square Wave Duty Cycles
a. Set-Up:
AMPLITUDE Midrange
RANGE 1K
FUNCTION Square Wave
FREQ/10 Button In
FREQ DIAL 3.0
b. Test Scope Set-Up:
Volts/Div 1V
AC/GND/DC DC
Time/Div 0.2 mSec
Trig Slope +
c. Connect MAIN OUTPUT to test scope vertical input via coax cable and 50 ohm
terminator. Adjust Trig Level as necessary for a stable display.
d. Use test scope variable Time/Div control to set the display for 1 complete cycle
over 10 divisions.
e. Check for nearly equal positive and negative half cycles (50 % duty cycle).
Readjust the variable Time/Div as necessary to maintain 1 complete cycle over
10 divisions.
f. Set FREQ/10 button out.
g. Check that the frequency increases by a factor of 10 as shown by a display of
approximately 1 cycle per division on the test scope.
h. Set the FREQ/10 button in. Rotate the SYMMETRY knob CCW and use the
Time/Div variable to set the first half cycle to 1 division. Rotate the SYMMETRY
knob CW and check for the same half cycle to increase to 5 divisions or greater (a
duty cycle change of 5:1).
i. Return the SYMMETRY knob to the center detent position and the test scope
Time/Div variable to the detent position.

CFG253 Performance Verification & Adjustment Procedures
Page 8of 19 Procedure #: CP1005 Revision: A
j. Repeat steps d and e to verify the 50 % duty cycles for the settings in Table 4.
Table 4
RANGE FREQ. DIAL FREQ/10 TIME/DIV RESULT
1K 3.0 OUT 20uSec 50 % Duty Cycle
1K 0.3 OUT 0.2mSec 50 % Duty Cycle
1K 0.3 IN 2 MSec 50 % Duty Cycle
100K 0.3 OUT 2 uSec 50 % Duty Cycle
1M 0.3 IN 2 uSec 50 % Duty Cycle
5. SYNC (TTL) OUTPUT
a. Set-Up:
AMPLITUDE CW
RANGE 1K
FUNCTION Triangle
VOLTS OUT Button Out
FREQ/10 Button Out
FREQ DIAL 3.0
b. Test Scope Set-Up:
Volts/Div 1 V
Time/Div 0.2 mSec
c. Connect SYNC/TTL OUTPUT directly to the test scope vertical input via a coax
cable (without the 50 ohm terminator).
d. Check the test scope for a display of approximately 4 volts (4 divisions).
e. Repeat step d with the FUNCTION set to Square Wave and Sine Wave.

CFG253 Performance Verification & Adjustment Procedures
Page 9of 19 Procedure #: CP1005 Revision: A
6. SINE WAVE DISTORTION
a. Set-Up:
RANGE 100K
FUNCTION Sine Wave
VOLTS OUT Button Out
FREQ/10 Button Out
FREQ DIAL 1.0
b. Connect MAIN OUTPUT to Distortion Analyzer via coax cable and 50 ohm
terminator.
c. Set the Distortion Analyzer INPUT RANGE to Auto Range, and the FUNCTION
settings to Volts, Auto Range and THD+N.
d. CHECK- For less than 1% distortion for the frequencies listed in Table 5:
Table 5
RANGE FREQ DIAL PER CENT
DISTORTION
100K 1.0 < 1 %
10K 1.8 < 1 %
1K 1.8 < 1 %
100 1.8 < 1 %
10 1.0 < 1 %
7. FREQUENCY DIAL ACCURACY
a. Set-Up:
AMPLITUDE CW
RANGE 1K
FUNCTION Triangle
VOLTS OUT Button In
FREQ/10 Button Out
FREQ DIAL 3.0

CFG253 Performance Verification & Adjustment Procedures
Page 10 of 19 Procedure #: CP1005 Revision: A
b. Connect the CFG253 MAIN OUTPUT to the input of a Frequency Counter.
Check the frequency reading for each set-up listed in Table 6:
Table 6
RANGE FREQ DIAL COUNTER READING
1 M 3.0 2.85 MHz - 3.15 MHz
1 M 0.3 150 KHz - 450 KHz *
100 K 3.0 285 KHz - 315 KHz
10 K 3.0 28.5KHz - 31.5KHz
1 K 3.0 2.85KHz - 3.15KHz
100 3.0 285 Hz - 315 Hz
10 3.0 28.5 Hz - 31.5 Hz
13.0 2.85 Hz - 3.15 Hz
*The Frequency reading accuracy is 5% of full scale. 5% of 3 MHz is 150
KHz
c. Disconnect cable from the Counter and CFG253.

CFG253 Performance Verification & Adjustment Procedures
Page 11 of 19 Procedure #: CP1005 Revision: A
CFG253 ADJUSTMENT PROCEDURE
NOTE:
The Adjustment procedure should be performed only by
qualified service technicians.
CONTENTS:
Preparation 11
Test equipment requirements 12
Set U1 input voltage 12
Set Q5 gate voltage 12
Adjust square wave duty cycle 13
Set DC offset 14
Square wave overshoot, rise and fall times 15
Set output levels 15
Sine wave distortion 16
Frequency dial accuracy 17
Reassembly 19
PREPARATION FOR ADJUSTMENT
This procedure should be accomplished at an ambient temperature of 21 to 25 degrees C and
a relative humidity of 75% or less.
It is necessary to remove the bottom cover from the instrument to gain access to the
adjustments used in this procedure.
Turn off the POWER switch, disconnect the power cord and place the CFG253 upside down
on its top.
Remove the 2 screws in the rear feet and the 2 screws BESIDE the front feet.
Carefully lift the bottom cover off the unit, remove the handle and set these aside along with
the screws for later reassembly.
Reconnect the power cord from an appropriate AC power source and allow the instrument a
20 minute warm up period.

CFG253 Performance Verification & Adjustment Procedures
Page 12 of 19 Procedure #: CP1005 Revision: A
Test Equipment requirements
The test equipment listed in the Table on Page 2 is a list of the equipment needed for
this performance check. All test equipment is assumed to be operating within
tolerance. Detailed operating instructions for test equipment are not given in this
procedure. If operating information is needed, refer to the appropriate test equipment
instruction manual.
Initial CFG253 Set-Up:
AMPLITUDE CCW
DC OFFSET Pushed In
SYMMETRY Midrange Detent
RANGE 1K
FUNCTION All Buttons Out
VOLTS OUT Button Out
FREQ/10 Button Out
SWEEP Button Out
SWEEP RATE Midrange
SWEEP WIDTH Midrange
FREQ DIAL 0.3
1. Set U1 Input Voltage
a. Set digital multimeter to DC mV range
b. Connect multimeter test leads to pins 2 and 3 of Integrated Circuit U1.
Note: Alternate Test Points
Locate R8 and R9 at the front left edge of the Main circuit board.
Pin 2 is connected to the end of R8 nearest the board edge. Pin 3 is
connected to the end of R9 furthest from the board edge.
c. Adjust R10 for approximately 0 mV.
2. Set Q5 Gate Voltage
a. Connect common lead of multimeter to ground and the positive lead to the wire
loop test point near gate of Q5. (on the Main board under rear edge of the
elevated Switch board).
b. Adjust R33 for approximately 0 mV.

CFG253 Performance Verification & Adjustment Procedures
Page 13 of 19 Procedure #: CP1005 Revision: A
3. Adjust Square Wave Duty Cycles
a. Set-Up:
AMPLITUDE Midrange
RANGE 1K
FUNCTION Square Wave
FREQ/10 Button In
FREQ DIAL 3.0
b. Test Scope Set-Up:
Volts/Div 1V
AC/GND/DC DC
Time/Div 0.2 mSec
c. Connect MAIN OUTPUT to test scope vertical input via coax cable and 50 ohm
terminator. Adjust Trig Level as necessary for a stable display.
d. Use test scope variable Time/Div control to set the display for 1 complete cycle
over 10 divisions.
e. Adjust R67 for equal positive and negative half cycles (50 % duty cycle).
Readjust the variable Time/Div as necessary to maintain 1 complete cycle over
10 divisions.
f. Set FREQ/10 button out.
g. Adjust R126 for 1 cycle per division on the test scope.
h. Repeat steps d and e to set the 50 % duty cycles for the settings and adjustments
in Table 1.
Table 1
RANGE FREQ. DIAL FREQ/10 TIME/DIV ADJUST RESULT
1K 3.0 OUT 20uSec R127 50 % Duty Cycle
1K 0.3 OUT 0.2mSec R18 50 % Duty Cycle
1K 0.3 IN 2 MSec R16 50 % Duty Cycle
100K 0.3 OUT 2 uSec R132 50 % Duty Cycle
1M 0.3 IN 2 uSec R128 50 % Duty Cycle

CFG253 Performance Verification & Adjustment Procedures
Page 14 of 19 Procedure #: CP1005 Revision: A
4. Set DC Offset
a. Set-Up:
DC OFFSET Pulled Out
RANGE 1K
FUNCTION All Buttons Out
VOLTS OUT Button Out
FREQ/10 Button Out
b. Test Scope Set-Up:
Volts/Div 2V
Time/Div 0.2 mSec
Var Time/Div Cal
c. Connect MAIN OUTPUT to test scope vertical input via coax cable and 50 ohm
terminator.
d. Set test scope Vert Coupling to GROUND, center the trace, then set Coupling
back to DC.
e. While turning the DC OFFSET knob from CCW to CW and back, adjust R117 for
equal voltage swings positive and negative on the test scope.
f. Adjust R129 for 5.1 V with DC OFFSET knob CW and -5.1 V with the knob CCW
(2.55 Div on test scope). Repeat step e, if necessary.
g. Push the DC OFFSET knob in (off).
h. Set the test scope to 10 mV/Div.
i. Set test scope Vert Coupling to GROUND, center the trace, then set Coupling
back to DC.
j. Slowly adjust R82 to recenter the trace, set to within 1 division of center (+/- 10
mV).

CFG253 Performance Verification & Adjustment Procedures
Page 15 of 19 Procedure #: CP1005 Revision: A
5. Square Wave Overshoot, Rise Time and Fall Time
a. Test Scope Set-Up:
Volts/Div 5V
Time/Div 0.5 uSec
Trig Slope +
b. Set-Up:
AMPLITUDE CW
DC OFFSET Pushed In
RANGE 100K
FUNCTION Square Wave
VOLTS OUT Button Out
FREQ/10 Button Out
FREQ DIAL 3.0
c. Connect MAIN OUTPUT to test scope vertical input via coax cable WITHOUT
the 50 ohm terminator.
d. Adjust AMPLITUDE knob for a 4 division display on the test scope.
e. Adjust C31 for minimum overshoot (will not be completely flat).
f. Set Time/Div to 50 nSec/Div. Adjust Trig Level control as necessary to display
the rising edge of the Square Wave.
g. Check risetime between the 10% and 90% points for < 100 nSec (2 Div).
h. Set test scope Trig Slope to - (negative). Adjust Trig Level to view the Falling
edge of Square Wave.
i. Check the Fall Time between the 10% and 90% points for < 100 nSec (2 Div).
6. Set OUTPUT Levels
a. Set-Up:
AMPLITUDE CW
DC OFFSET Pushed In
RANGE 1K
FUNCTION Triangle
VOLTS OUT Button Out
FREQ/10 Button Out
FREQ DIAL 3.0

CFG253 Performance Verification & Adjustment Procedures
Page 16 of 19 Procedure #: CP1005 Revision: A
b. Test Scope Set-Up:
Volts/Div 2V
Time/Div 0.2 mSec
Trig Slope +
c. Connect MAIN OUTPUT to test scope vertical input via coax cable and 50 ohm
terminator.
d. Adjust R130 for approximately 10.5 V p-p output display on test scope (5.25
Div).
e. Set RANGE to 1M and FREQ DIAL to 0.3.
f. Note the test scope display amplitude.
g. Observe the display amplitude for > 10 V while turning the FREQ DIAL from 0.3
to 3.0.
h. Set the FREQ DIAL to 3.0. Adjust C55 for the same amplitude as observed in
step f.
i. Repeat steps a thru h for the Sine Wave function. In step d, adjust R74 for 10.8
V. In step h, use C26.
j. Set FUNCTION to Square Wave, RANGE to 1K and FREQ DIAL to 3.0.
k. Adjust R56 for approximately 10.8 V on the test scope display (5.4 Div).
7. Sine Wave Distortion
a. Set-Up:
RANGE 100K
FUNCTION Sine Wave
VOLTS OUT Button Out
FREQ/10 Button Out
FREQ DIAL 1.0
b. Connect the MAIN OUTPUT to the Distortion Analyzer via a coax cable and a 50
ohm terminator.

CFG253 Performance Verification & Adjustment Procedures
Page 17 of 19 Procedure #: CP1005 Revision: A
c. Set the Distortion Analyzer INPUT RANGE to Auto Range and the FUNCTION
settings to Volts, Auto Range and THD+N.
d. Adjust R43 and R46 for a minimum distortion reading on the Distortion
Analyzer. Repeat the two adjustments as necessary to obtain the optimum
results.
e. Disconnect the cable from the Distortion Analyzer.
*** Alternate Procedure ***
( If Distortion Analyzer is not available )
f. Test Scope Set-Up:
Volts/Div 2V
Time/Div 1 uSec
g. Connect MAIN OUTPUT to test scope vertical input via coax cable and 50 ohm
terminator.
h. Adjust R46 for minimum distortion at top of sinewave and R43 for minimum
distortion at the bottom.
7. FREQUENCY DIAL ACCURACY
a. Set-Up:
AMPLITUDE CW
RANGE 1K
FUNCTION Triangle
VOLTS OUT Button In
FREQ/10 Button Out
FREQ DIAL 3.0
b. Connect the MAIN OUTPUT to the input of a Frequency Counter.
NOTE:
If a Frequency Counter is not a available, see
alternate procedure on next page.
c. Adjust R6 for a reading of 3.0 KHz on the Frequency Counter.

CFG253 Performance Verification & Adjustment Procedures
Page 18 of 19 Procedure #: CP1005 Revision: A
d. Set the RANGE to 1M and adjust C8 for a reading of 3.0 MHz on the Frequency
Counter.
e. Check the Frequency Counter readout while changing the CFG253 FUNCTION
between Sine Wave and Square Wave. Adjust R76 for approximately 3.0 MHz,
setting for the best compromise between Sine Wave and Square Wave.
*** Alternate Procedure ***
( If a Frequency Counter is not available )
f. Set-Up:
AMPLITUDE CW
RANGE 1K
FUNCTION Triangle
VOLTS OUT Button Out
FREQ/10 Button Out
FREQ DIAL 3.0
g. Test Scope Set-Up:
Volts/Div 0.5 V
Time/Div 0.2 mSec
h. Connect SYNC/TTL OUTPUT to test scope vertical input via coax cable and 50
ohm terminator.
i. Adjust R6 for a display of 6 cycles in 10 Divisions on the test scope. (3KHz)
j. Set RANGE to 1M and the test scope Time/Div to 0.2 uSec.
k. Adjust C8 for a display of 6 cycles in 10 Divisions on the test scope. (3MHz)
l. Check display while changing the FUNCTION between Sine Wave and Square
Wave. Adjust R76 for 6 cycles in 10 Divisions, setting for the best compromise
between Sine Wave and Square Wave frequencies.

CFG253 Performance Verification & Adjustment Procedures
Page 19 of 19 Procedure #: CP1005 Revision: A
REASSEMBLY
1. Disconnect any cables connected to the CFG253, turn off the POWER switch and
remove the power cord.
2. With the unit setting upside down on its top, place the handle upside down in
its opening in the case top and carefully slide the case bottom onto the unit. Be
sure that the front and back grooves line up and slip over the front and rear
panels.
3. Reinstall the two rear feet and screws plus the two front screws.