Table Of Contents - Tektronix 491 Maintenance Manual

CALIBRATION RECORD AND INDEX
This Abridged Calibration Procedure is provided to aid in
checking the operation of the Type 491/R491.
as a calibration guide by the experienced calibrator, or as a
calibration record. Since the step number and titles used
here correspond to those in the complete Calibration Proce-
dure, the following procedure serves as an index to locate a
step in the complete Calibration Procedure. Characteristics
are those listed in the Characteristics section of the instruction
manual.
Type 491, Serial No.
C a l i b r a t i o n D a t e
Calibrator
1.
Adjust the -10 Volt Supply.
If voltage is not within tolerance (±1%]adjust R968
for -10 volts.
2.
Check the +10 Volt and +150 Volt Supplies. Page 6-9
3. Adjust the High Voltage Power Supply.
Measure high voltage between pin 14 of CRT and
chassis ground.
Adjust R1000 for 3670 volts.
4. Adjust Intensity Range.
Remove F1008 and connect ammeter across the fuse
holder. Adjust R1032 for 750 mA. Be careful not to
exceed 800 mA.
5. Check Power Supply Voltage Regulation. Page 6-10
Refer to Table 6-2.
6. Adjust Trace Alignment.
Adjust R1035 to align trace with horizontal graticule
line.
7.
Adjust Vertical Amplifier Gain.
With 0.5 volt signal applied to pin H of Vertical Amp.
board, adjust R873 for 5 division display.
8. Check Range of Vertical POSITION control. Page 6-13
A 0.5 volt signal applied to pin H of the Vertical
Amplifier should position out of the graticule area
when the Vertical Position control is in either extreme
position.
9. Adjust Trigger Level Centering.
Adjust LEVEL control for zero volts at pin C of Hori-
zontal Display board, then adjust Trig Level Center
R724, far stable sweep triggering with + and -
SLOPE on an internal signal with an amplitude of
0.2 divisions.
10. Check External Triggering.
Check triggering with an externally applied signal
with an amplitude ≥0.2 V and a frequency between
20 Hz and 100 kHz.
11. Check Line Triggering.
Apply the line signal from pin 17 of the power trans-
former through a 10× attenuator probe, to pin H on
the Vertical Amplifier board. Check operation of
LINE trigger on + and - SLOPE positions.
12.
It
may be used
13.
14.
15.
Page 6-8
16.
17.
Page 6-9
18.
Page 6-10
19.
Page 6-11
20.
Page 6-13
21.
22.
Page 6-14
23.
Page 6-15
Page 6-16
Adjust Sweep Length,
Adjust Sweep Length R759, for 7.5 volt peak to peak
sawtooth, at pin S of the Horizontal Display board.
Adjust Sweep Calibration and Sweep Gain. Page 6-17
Adjust Sweep Gain R813, for 10,5 division sweep
length. Adjust Sweep Cal R787, for calibrated sweep.
Use 1 ms timing markers applied to pin H of Vertical
Amplifier board to calibrate sweep timing.
Check Sweep Timing Accuracy.
Check sweep timing accuracy (±3%), for all posi-
tions of the TIME/DIV selector.
Check VARIABLE Control Range.
VARIABLE control range ³2.5:1.
Check SAW OUT Signal Amplitude.
Check amplitude of sawtooth signal at SAW OUT
connector. Should measure between 70 and 90 mV.
Check Unblinking Waveform.
Check unblinking waveform at pin K of Horizontal
Display board. Should measure between 0.8 and 1.0
volt, typically 0.9 V.
Adjust RF Amplitude.
Adjust the RF Ampl R290, for -0.85 volt ±0.1 V at
pin, P of square pin connector on the honeycomb
assembly.
Adjust Center Frequency Range.
Apply 200 MHz to the RF INPUT connector. Adjust
Center Freq Range R251, for minimum IF signal shift
as the DISPERSION selector is switched through the
MH/div range.
Adjust Sweep Center.
Apply a 200 MHz signal to the band B RF INPUT
connector. Adjust Sweep Center R203, to center the
200 MHz signal on the sweep.
Adjust MHz/Div Dispersion and Linearity. Page 6-20
Apply 10 MHz (.1 /µs) and 10 ns markers to RF INPUT
from the Time-Mark Generator. Adjust DISPERSION
CAL R208 and C358 for dispersion accuracy and
linearity,
Check Dispersion Accuracy of the MHz/ Page 6-22
DIV Ranges and the IF CENTER FREQ Controls.
Check the dispersion accuracy for each MHz/div
position of the DISPERSION selector as listed in Table
6-3.
Adjust IF Amplifier Response and
Resolution Bandwidth.
Adjust L144, T464, T454, C435, C425 for maximum
response to an IF feedthrough signal with the GAIN
control fully clockwise. Adjust L444 for stable 70
MHz oscillator operation.
Set the DISPERSION to 50 kHz/div, RESOLUTION
fully clockwise, Connect a 10× probe from the
test oscilloscope to pin B of the honeycomb assembly.
Adjust C504, C508, C601, C604, C607 and C610 for
optimum display symmetry and maximum ampli-
tude with no more than 3 dB dip in the center. Set
Page 6-17
Page 6-18
Page 6-18
Page 6-18
Page 6-19
Page 6-19
Page 6-19
Page 6-19
Page 6-23
6-5