Adjust Sweep Length,
CALIBRATION RECORD AND INDEX
Adjust Sweep Length R759, for 7.5 volt peak to peak
This Abridged Calibration Procedure is provided to aid in
sawtooth, at pin S of the Horizontal Display board.
checking the operation of the Type 491/R491. It may be used
Adjust Sweep Calibration and Sweep Gain. Page 6-17
as a calibration guide by the experienced calibrator, or as a
calibration record. Since the step number and titles used
Adjust Sweep Gain R813, for 10,5 division sweep
here correspond to those in the complete Calibration Proce-
length. Adjust Sweep Cal R787, for calibrated sweep.
dure, the following procedure serves as an index to locate a
Use 1 ms timing markers applied to pin H of Vertical
step in the complete Calibration Procedure. Characteristics
Amplifier board to calibrate sweep timing.
are those listed in the Characteristics section of the instruction
Check Sweep Timing Accuracy.
Check sweep timing accuracy (3%), for all posi-
Type 491, Serial No.
tions of the TIME/DIV selector.
Check VARIABLE Control Range.
VARIABLE control range 2.5:1.
1. Adjust the 10 Volt Supply.
Check SAW OUT Signal Amplitude.
If voltage is not within tolerance (1%]adjust R968
Check amplitude of sawtooth signal at SAW OUT
for 10 volts.
connector. Should measure between 70 and 90 mV.
2. Check the +10 Volt and +150 Volt Supplies. Page 6-9
Check unblinking waveform at pin K of Horizontal
3. Adjust the High Voltage Power Supply.
Display board. Should measure between 0.8 and 1.0
Measure high voltage between pin 14 of CRT and
volt, typically 0.9 V.
Adjust R1000 for 3670 volts.
Adjust RF Amplitude.
Adjust the RF Ampl R290, for -0.85 volt 0.1 V at
4. Adjust Intensity Range.
pin, P of square pin connector on the honeycomb
Remove F1008 and connect ammeter across the fuse
holder. Adjust R1032 for 750 mA. Be careful not to
exceed 800 mA.
Apply 200 MHz to the RF INPUT connector. Adjust
5. Check Power Supply Voltage Regulation. Page 6-10
Center Freq Range R251, for minimum IF signal shift
as the DISPERSION selector is switched through the
6. Adjust Trace Alignment.
Adjust R1035 to align trace with horizontal graticule
Adjust Sweep Center.
Apply a 200 MHz signal to the band B RF INPUT
connector. Adjust Sweep Center R203, to center the
7. Adjust Vertical Amplifier Gain.
200 MHz signal on the sweep.
With 0.5 volt signal applied to pin H of Vertical Amp.
board, adjust R873 for 5 division display.
Adjust MHz/Div Dispersion and Linearity. Page 6-20
Apply 10 MHz (.1 /s) and 10 ns markers to RF INPUT
8. Check Range of Vertical POSITION control. Page 6-13
from the Time-Mark Generator. Adjust DISPERSION
A 0.5 volt signal applied to pin H of the Vertical
CAL R208 and C358 for dispersion accuracy and
Amplifier should position out of the graticule area
when the Vertical Position control is in either extreme
Check Dispersion Accuracy of the MHz/ Page 6-22
DIV Ranges and the IF CENTER FREQ Controls.
9. Adjust Trigger Level Centering.
Check the dispersion accuracy for each MHz/div
Adjust LEVEL control for zero volts at pin C of Hori-
position of the DISPERSION selector as listed in Table
zontal Display board, then adjust Trig Level Center
R724, far stable sweep triggering with + and -
Adjust IF Amplifier Response and
SLOPE on an internal signal with an amplitude of
Adjust L144, T464, T454, C435, C425 for maximum
Check External Triggering.
response to an IF feedthrough signal with the GAIN
Check triggering with an externally applied signal
control fully clockwise. Adjust L444 for stable 70
with an amplitude ≥0.2 V and a frequency between
20 Hz and 100 kHz.
Set the DISPERSION to 50 kHz/div, RESOLUTION
fully clockwise, Connect a 10 probe from the
Check Line Triggering.
Apply the line signal from pin 17 of the power trans-
former through a 10 attenuator probe, to pin H on
Adjust C504, C508, C601, C604, C607 and C610 for
optimum display symmetry and maximum ampli-
the Vertical Amplifier board. Check operation of
tude with no more than 3 dB dip in the center. Set
LINE trigger on + and - SLOPE positions.