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 replace-
ment 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 trouble-
shooting 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 the 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 Resis
tor. It may get open.
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