Date Code 20000421 Maintenance and Testing 7-29
SEL-251, -2, -3 Instruction Manual
Power Supply Voltages Test
Purpose: Verify that correct output voltages are presented to Port 1, Port 2R, and the auxiliary
port. These voltages are required by external devices including a dc powered modem
or the SEL-DTA and SEL-RD units.
Method: 1. Execute the STATUS command and inspect the voltage readings for the +5 and
±15 volt supplies.
2. At the Auxiliary Port, use a voltmeter to read the +5 and "12 volt outputs. The
12 volt outputs are derived from the 15 volt supplies using three-terminal
regulators. The following pins are the read points:
Pin 5: Ground
Pin 9: Ground
Pin 1: +5 Vdc
Pin 4: +12 Vdc
Pin 6: -12 Vdc
Figure 7.5: Nine-Pin Connector Pin Number Convention
3. Compare the +5 volt readings from the status report and voltmeter. The voltage
difference should be less than 50 mV, and both readings should be within 0.15
volts of five volts.
The 12 volt supplies should be within 0.5 volts of their nominal values.
RELAY CALIBRATION
The SEL-251 Relay is factory calibrated. If you suspect that the relay is out of calibration,
please contact the factory.
TROUBLESHOOTING
Inspection Procedure
Complete the following procedure before disturbing the system. After you finish the inspection,
proceed to the Troubleshooting Table.
1. Measure and record control power voltage at terminals 44 and 45.
2. Check to see that the power is on, but do not turn system off if it is on.
3. Measure and record the voltage at all control inputs.
(female chassis connector, as viewed from outside panel)
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