i. Adjust the Brightness and Focus. Refer to Appendix E, Monitor Board Power
Supply Schematic, sections A-23 and B-24.
(1) Start with a brightness setting by adjusting R85, which gives an acceptable
trace reading with the light filter in position. Next, turn R80 (one-turn control) focus adjust
to the best trace definition possible, both vertical and horizontal, since this CRT doesn't
need astigmatism adjustment.
(2) If the trace is getting too bright once you correct focus, reduce the
brightness by turning R85 to a more suitable value. If these adjustments are not turning
out satisfactorily, check the fixed dc voltage on pins 2 and 6 of the CRT (+360v
approximately) and also the high voltage on the second anode of the CRT.
(3) Since this electrode is taking only about 5.0 microamperes under normal
brightness condition, any additional load by the voltmeter probe has to be kept as low as
possible. In practice, we found that a 1000 meg ohm (meg) probe introduces a minus error
of about 6 percent without disturbing the filtering. So a reading of 4.9 kilovolt (kv) with the
probe means that the true anode voltage is close to 5.1kv.
Discharging the high voltage through short-circuit may cause permanent
damage to the caper military occupational specialty (CMOS) circuits. Use a
1meg, 1w resistor to discharge the high voltage.
Do not operate the CRT below 4.0kv or above 6.5kv.
CALIBRATE THE GROUNDED ANALOG AMPLIFIER
In this section, it is assumed that the power supply assembly and the preamplifiers
(patent cable and paddle) are already completely adjusted. Perform the following
procedures to calibrate the grounded analog amplifier.
a. Calibrate the Monitor. Refer to Appendix A, Monitor Board Pre-Amp
Schematic, section C-4.
(1) Adjust the dc offset control, R33, so as to present 0v to 0.02v positive at
pin 9 of the voltage to frequency converter. This voltage should never read negative.
(2) This calibration should be done with no input signal or all patient leads
b. Calibrate the FM Detector. Refer to Appendix B, Monitor Board Analog
Schematic, section C-6.
(1) With lead 1 position RA, LA, and LL shorted together, connect the
voltmeter to pin 7 of U101 and adjust R102 (four-turn control) to the lowest possible dc
offset voltage as shown by the digital voltmeter.