Service manual

Testing the Power Supply
4-19
4Testing the Power Supply
Use this procedure to check the voltages produced by the power supply. The cardiograph
must be connected to AC power to test all the power supply voltages. All the voltage
measurements are taken with respect to ground, unless indicated. Refer to Figure 4-2 for
voltage test point locations.
When the cardiograph is connected to AC power, there are dangerous voltages
present in the areas indicated in Figure 4-2 and on the Capacitor Assembly. Do
not touch any exposed metal while the cardiograph is open and AC power is
connected.
1. Open the top cover assembly as described in Chapter 5.
2. Without replacing the top cover, plug the keyboard cable into J201.
3. With the battery removed, plug the unit into AC power.
Be very careful to not short any signal to ground or to other pins. This will result in
cardiograph failure.
4. Verify AC LED is lit. If it is not lit, measure ACON between ground and the back-
plane pin 5 of J3. It should read approximately 5 Vdc. The presence of this voltage
confirms the proper operation of the primary transformer, fuses and ACON regulator
circuit.
5. Measure VSEC between the anode of CR1 (-VSEC) and the cathode of CR8
(+VSEC). It should read approximately 25 Vdc. The presence of this voltage con-
firms the proper operation of the mains transformer/primary power circuit and the
secondary rectifier filter.
6. Measure VBAT between ground and the point marked VBAT. It should read approx-
imately 6.7 (minimum) to 7.03 (maximum) Vdc @ 25° C. This voltage confirms the
proper operation of the battery charger.
The voltage range for environments with temperatures other than 25° C can be calculated
from the following equations:
Vmin = [2.220 - (T - 25)3.9×10
-3
]3.016, where T = temperature in °C
Vmax = [2.315 - (T - 25)3.9×10
-3
]3.024
7. Measure UNSW+5V between ground and the point marked UNSW+5V. It should
read 5 Vdc. Its presence confirms the proper operation of the unswitched 5 volt regu-
lator.
WARNING
CAUTION
NOTE