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checked by substituting a new component for it ( or one which has been checked
previously). However, be sure that circuit conditions are not such that a
replacement transistor might also be damaged. If substitute transistors are not
available, use a dynamic tester. Static-type testers are not recommended, since
they do not check operation under simulated operating conditions. An approved
anti-static suction-type desoldering tool must be used to remove soldered-in
transistors.
Integrated circuits can be checked with a voltmeter, test oscilloscope, or by
direct substitution. A good understanding of the theory of operation is essential to
troubleshooting circuits using IC's. Operating waveforms, logic levels, and other
operating information for the IC's are given in the theory of operation. Use care when
checking voltages and waveforms around the IC's so that adjacent leads are not shorted
together. A convenient means of clipping a test probe to the 14 pin in-line IC is with an
integrated circuit test clip. This device also doubles as an extraction tool.
5.2.9 DIODES : Do not use an ohmmeter that has a high internal current. High currents
may damage a diode. A diode may be checked for an open or shorted condition by
measuring the resistantce. With an ohmmeter scale having an internal source of
between 800mV and 1.5V, the resistance should be very high in one direction and
very low when the leads are reversed.
5.2.10 RESISTORS : Check the resistors with an ohmmeter. Resistor tolerances are
given in the Electrical Parts List. Resistors do not normally need to be replaced
unless the measured value varies widely from the specified value.
5.2.11 CAPACITORS : A leaky or shorted capacitor can be detected by checking
resistance with an ohmmeter on the voltage rating of the capacitor. The resistance
reading should be high after initial charge of the capacitor. An open capacitor can best
be detected with a capacito meter, or by checking whether it passes ac signals.
5.3 REPAIRS & MAINTENANCE :
5.3.1 Remove the mains cord from the source before removing top cover of the unit.
5.3.2 To open the cover, remove screws from Top & Bottom Covers. Disconnect
Grounding of both covers.
5.3.3 If there is no output, check the input supply Voltage and the Fuse continuity, etc.
Check both Fans are working
5.3.4 If the output is high and unregulated, check for open Voltage adjust potentiometer
or shorted mosfet, etc.
5.3.5 Similarly, if the current is unregulated, check for value change in the Shunt
Resistor. It may get open.
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