THEORY OF OPERATION
screen. The amount of this signal added to the ramp is adjusted by the S potentiometer RV4. This allows
adjustment of linearity between the edges and the center of the screen.
Using the adjustments described above, it is possible to achieve a linear signal across the entire crt screen for any
crt. These adjustments should be done whenever a crt or Mother Board is replaced. The complete horizontal
deflection signal including correction is summed at U7 Pin 2 and goes through amplifier U7 and transistors Q3, Q4,
Q7 & Q8.
Unblanking
The unblanking (Z) signal indicates when to brighten the crt. This signal is created in the digital section. For the
raster display, short pulses cause the brightening of each dot needed to generate the characters to be displayed. For
the stroke portion, the signal is high during the entire horizontal sweep displaying the ECG waveform.
Audio Circuits
Two types of audio is produced by the monitor: a QRS beep and an alarm tone. The QRS beep is a short tone that is
generated each time a QRS complex is detected by the monitor. The alarm tone is produced when any of the alarms
are triggered. The alarm tone can be disabled by pressing the front panel
ON/OFF button.
ECG Audio
The audio signal originates in the digital circuitry. The ECG AUD signal is enabled at U51 by an output from the
processor's I/O port U51 Pin 11. This signal allows the audio frequency from U51 to be passed to the audio
amplifier. Two levels of ECG AUD, through resistor R90, go to the rear panel QRS VOLUME switch as AUDIO
HI and AUDIO LO, where the user can select a high, low, or off setting. The selected signal then goes to the audio
amplifier U13 and transistors Q19 and Q20, which drive the speaker.
Alert Audio
The ALRT AUDIO is enabled by the output from U36 Pin 18 in the digital circuit The ALERT AUD signal passes
through volume adjust potentiometer RV11 to the audio amplifier U13.
Model 101R/NR Service Manual 33
To Next Page
Loading...
Need help?
General
