B&K 1794 instruction manual Repairs & Maintenance

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.

5.2.9DIODES : 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.

5.2.11CAPACITORS : 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.

5.3REPAIRS & MAINTENANCE :

5.3.1Remove the mains cord from the source before removing top cover of the unit.

5.3.2To open the cover, remove screws from Top & Bottom Covers. Disconnect Grounding of both covers.

5.3.3If there is no output, check the input supply Voltage and the Fuse continuity, etc. Check both Fans are working

5.3.4If the output is high and unregulated, check for open Voltage adjust potentiometer or shorted mosfet, etc.

5.3.5Similarly, if the current is unregulated, check for value change in the Shunt Resistor. It may get open.

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