proceeding to the next step. The digital meter doesn’t have a zero adjustment and the full
scale is on the back of the meter, or on the A100 PCB R406 or R402.
5.3.2 VOLTAGE CHANNEL AND VOLTMETER CALIBRATION
1. Disconnect any load from output of the power supply.
2. Connect a digital voltmeter across output terminals.
3. Turn the Voltage control completely counterclockwise and Current control clockwise.
4. Apply input power and turn the circuit breaker on.
5. While monitoring the voltmeter that is across the output terminals, adjust R55 until the
power supply output voltage starts to increase in the normal polarity. Adjust R55 in the
opposite direction until the output voltage decreases to zero. Do not continue adjustment
past this point.
6. Rotate Voltage control fully clockwise. While monitoring the voltmeter that is across the
output terminals, adjust R3 until voltage across output terminals is equal to the
maximum rated output voltage of the power supply.
7. The front panel voltmeter should agree within 2%. If it does not, adjust the
potentiometer that is located on the front panel voltmeter (adjust R406 on A100 bd. if
unit is a 600w/ 1KW) and check its zero adjustment if voltmeter is analog, (digital meter
has no Zero Adjustment).
8. Turn circuit breaker off.
5.3.3 Current Channel and Ammeter Calibration
9. Connect a short across the output terminals of the power supply.
10. Connect a millivoltmeter across the current shunt sense terminals observing correct
polarity.
11. Turn the Voltage control clockwise and the Current control completely
counterclockwise.
12. Turn the circuit breaker on.
13. Adjust R47 (or R77 if unit is a 5KW ) until the voltage across shunt starts to increase.
Adjust R47 (or R77) in the opposite direction until the voltage across shunt decreases to
zero. Do not continue adjustment past this point.
14. Turn Current control completely clockwise. Adjust R5 until voltage across sense
terminals of the shunt is equal to the rated voltage of the shunt which in most cases is
100 mV. Some power supplies (usually high current units) are equipped with a 50 mV
shunt.
15. The front panel Ammeter should read the maximum output current of the power supply.
If not, adjust the potentiometer that is located on the front panel ammeter. If the unit is
a 600W/1KW adjust R402 which is located on the A100 Bd, the digital meter has no
Zero Adjustment.
16. Turn circuit breaker off.
17. Disconnect the AC input power.
83-473-000 Revision J
5 - 2 Calibration and Troubleshooting
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