6-4
JQE SPECIAL SVC 092611
• If the unit is operated at full power with maximum input voltage, check that the ambient
operating temperature surrounding the unit is within specified limits (see PAR 1.5).
• Verify that the pass-element transistors are tight to the heat sink and that silicone grease
was used between the transistor and heat sink. If problem recurs, replace thermoswitch
mounted on heat sink assembly.
4. If the power supply is basically functioning, but poor performance is evident, inspect the test
set-up to make certain the source of the trouble is not external.
5. Poor regulation in any of the regulating modes is usually traceable to incorrectly connected
loads or faulty measurement techniques. Perform measurements as described in Paragraph
6.4.2.
6. Oscillation of the output voltage or output current is often due to a load with a large inductive
component. Twisted load wires of sufficient diameter and held as short as practical, are often
the solution to the problem.
7. Kepco Application Engineers are available for consultation or direct help in difficult service or
application problems.
6.4
POWER SUPPLY MEASUREMENTS
Measurement of the significant parameters of a power supply is a requirement for incoming
inspection, periodic maintenance, or after component replacement. Since the measurements
require special techniques to ensure correct results, suggestions for their performance are given
below.
6.4.1
REQUIRED TEST EQUIPMENT.
1. Constant AC supply voltage with provisions for “stepping” the voltage over a specified
region (105-125V); a variable autotransformer is generally adequate, if it is rated to
deliver the input current of the unit under test.
2. Resistive load, variable, with ON/OFF and SHORTING SWITCH and capable of dissi-
pating the full output power of the unit under test.
3. DC voltage monitor, digital voltmeter, or power supply analyzer.
4. Precision Current sensing resistor, for current regulation measurements, four-terminal
device.
5. AC ripple monitor, sensitivity better than 1 mV. Ballantine Model 302C. or Hewlett Pack-
ard Model 400H.
6. Optional: Oscilloscope, vertical sensitivity better than 0.1 mV/cm.
