Fresenius Medical Care 4008 E Technical Manual page 405

Alarm tone control and signal processing for both balancing chamber and stepper
motor trigger (circuit diagram 9/9)
Oscillator circuit:
The oscillator circuit consists of a binary counter IC 35, R53, R56, C35, C39, and Q2.
The output frequencies are active even with power failure, since U-Bat is fed to the 12-V supply
network via D18.
Power failure alarm:
In case of power failure, L level is applied to IC 31, pin 7. Since the output of IC 31, pin 5, becomes
highly resistive, approx. 9 V as well as the power failure frequency of 2048 Hz are applied to IC
31, pin 9, and are then directed to the output stage IC 45 (type TDA 7052) via IC 31, pin 20 and
pin 11.
Via the EN-PF-AT signal line, the power failure alarm tone is suppressed by means of H level at
IC 31, pin 7.
Balancing chamber dead time:
By means of the positive edge, the D-FF IC 17 is set (H level at pin 5) and the count-down unit IC
15 released at pin 9. The counter is decreased by 1 increment upon each positive clock pulse
edge. As soon as the counter reaches 0, pin 14 turns to L level, resetting the D-FF IC 17. By
means of L level at pin 9 of IC 15, the data of IC 16 is again called into the counter.
8-108
Fresenius Medical Care 4008 4/09.03 (TM)