Welch Allyn Atlas Service Manual page 102

5.4 Video Amplifier:
The CRT tube turns a dot on when video out is low (near 0V), and off when video out is high (+Vvid =
28V). The input to the video amplifier is a digital signal (3.3V logic level) from the uProcessor. An input
of 0V turns the dot off, an input of 3.3V turns the dot on. Transistor Q7 amplifies and inverts this signal.
Video out is driven low through D7, and driven high through emitter follower Q8. .
Video Amplifier
+5V
R51
19.6K
U4E
11
VideoIn
74HCT04
Recorder Electronics
6
6.1 Overview:
Atlas includes a thermal strip chart printer (optional on Model 200 and 210, standard on model 220). The
user can print either annotated waveform data or Patient trend information.
The printer specifications are:
Paper Size: 56 or 58mm
Printhead Width: 54mm
Resolution: Vertical: 8 dots/mm,
Horizontal: 12 dots/mm (300 dots/inch)
Chart Speed: 25mm/sec
The main CPU controls the printer. Data timing, clock signals, and strobe widths are all generated by the
FPGA on the CPU board. These signals are buffered on the recorder board (inverter U5), before
transmission to the printhead.
Appendix A
+Vvid
R36 R37
1.96K 1.96K
R48
100
10 u4-6 q7-g 2
(2 1/4 inches)
(2 1/8 inches)
(200 dots/inch)
(1 inch/second)
3
q8-b 2 Q8
1 2N3904
2 1 R41
681
D7 q8-e
1N4148
Q7
BS170
10/14/99
C19
.01uF
VideoOut