Tektronix 1L40, Instruction Manual

Page: 69 / 145

Performance C heck/Calibration— Type 1L40
Fig. 5 -1 5 . Phase lock circuit adjustments.
with minimum delay as the INT REF FREQ control is turned
from the OFF to the initial on position.
f. Set the DISPERSION RANGE to the kHz/CM position
and the DISPERSION to lOOkHz/cm.
g. Position the fixed marker signal (IF feedthrough of the
200th harmonic of the 1 MHz marker) to the graticule center
with the IF CENTER FREQ control. Adjust the RF CENTER
FREQ to decrease the number of interfering spurious signals
on the display.
h. CHECK— the pulling range of the INT REF FREQ control
on the reference oscillator frequency must equal 1 kHz or
more but less than 1.3 kHz.
Since the displayed signal is the 200th harmonic of
the internal reference oscillator frequency, the range is also
related to the 200th harmonic, therefore, 1 kHz X 200 = 200
kHz and 1.3 kHz X 200 = 260 kHz. W ith 100 kHz/cm disper­
sion the VARIABLE INT REF FREQ control should shift the
marker signal from 2 cm to a maximum of 2.6 cm.
If this performance requirement is not met, perform step
i.
i. ADJUST— L800 (Fig. 5-15) until the oscillator frequency
shift, over the range of the INT REF FREQ control, is 1.2 kHz
(2.4 cm).
j. CHECK— The accuracy of the internal 1 MHz reference
frequency as follows:
(1) A pply the 1 MHz markers from the Type 1L40 to
Channel 1 Input of a Dual-Trace Am plifier Plug-In Unit (Type
1A1) and 1 /<s markers from the Time-Mark Generator (Type
184) through a 10X attenuator and a
50 V. termination to
Channel 2 Input of the Dual Trace Amplifier.
(2) Adjust the deflection sensitivity for both channels of
the Dual-Trace Am plifier to equalize the deflection ampli­
tude, then set the Mode switch to Add.
(3) Set the test oscilloscope Time/Cm to 1 ms and adjust
the triggering controls for a triggered display.
(4) Turn the Type 1L40 INT REF FREQ control to the
initial on position (ccw) and check the beat frequency dis­
play for no more than 10 cycles in 10 cm (reference fre­
quency 1 MHz
±
1 kHz).
k. Check the electrical center of the CRT by connecting a
jumper between pins 1 and 3 of P-11 (interconnecting plug).
If the electrical center is more than 1 centimeter from the
graticule center, the vertical output amplifiers of the oscillo­
scope should be checked and repaired.
l
. Position the trace 3 cm below the electrical center with
the POS control.
m. Turn the FINE RF CENTER FREQ control fully counter­
clockwise. Depress the LOCK CHECK button and adjust the
Gate Bal, R840, to position the trace at or slightly below the
reference level established in step 1.
n. W ith the LOCK CHECK button depressed, rotate the
FINE RF CENTER FREQ control clockwise to position the trace
to the graticule center. Release the LOCK CHECK button.
NOTE
If the INT REF FREQ is turned O N , the d is p la y may
jump from one lock mode to the next as the FINE
RF CENTER FREQ co n tro l is ro ta te d clockwise.
NOTES
5-15