Heathkit IO-4550 - Page 27

0
(— 5a FR VN eee
CALIBRATION
This section of the Manual is divided into two parts: “Initial
Calibration’’ and ‘Touch-Up Adjustments.”” The “‘Initial
Calibration’ must always be performed after the
Oscilloscope has been serviced or parts have been replaced.
Page 25
The ‘Touch-Up Adjustments’ must always be performed
after the “Initial Calibration” and any time you doubt the
accuracy of your calibrated Oscilloscope.
INITIAL CALIBRATION
The following equipment is needed to calibrate your
Oscilloscope:
VTVM — Accurate to within 1% at 15 volts DC and
able to measure 1700 VDC.
Heathkit Oscilloscope Calibrator — OR — A Square
Wave Generator capable of producing 1 kHz to 1 MHz
signals; with up to 5 volts output, rise time <5 nS, and
overshoot <1%.
A 1000 Hz Square Wave Voltage Calibrator (1 to 100
volt output) is also recommended, but not necessary;
accurate in amplitude to 1% at 1 volt; accurate in
frequency to 1%.
Controls and adjustments associated with Channel Y1 are
identified as Y1, CH1, or a “-1" following the circuit
component number, such as R119-1. Channel Y2 controls
and adjustments are identified as Y2, CH2, or a “-2”
following the circuit component number. Use a plastic
alignment tool to make the adjustments.
If you do not obtain the proper results, turn the
Oscilloscope off, refer to the “In Case of Difficulty” section
of the Manual, and correct any difficulties before you
proceed.
Turn off the Oscilloscope and disconnect the line cord plug
from the AC power source.
Loosen the knurled knob on each side of the chassis and
remove the top and bottom covers. Be careful not to touch
any of the circuitry when you move the Oscilloscope around
for various adjustments. Dangerous voltages are present. See
Figure 23 (in the “Illustration Booklet”).
VOLTAGE ADJUSTMENTS
Refer to Parts A and B of Figure 15 (in the “Illustration
Booklet’’) for the following steps.
1. | Adjust your voltmeter to measure —15 volts DC.
2. Connect the common voltmeter lead to the
Oscilloscope chassis.
3. Measure the voltage at test point 4 (TP4, on the low
voltage circuit board). Adjust control R309 (on the
low voltage circuit board) for a —15 volt meter
indication. (Interchange your meter leads_ if
necessary.)
4. Adjust your voltmeter to measure —2000 volts DC.
5. Measure the voltage at lug 1 of control R2. Adjust the
H! VOLT ADJ control (R419, on the high voltage
circuit board) for —1700 volts DC (+10 volts).