B&K 1794 instruction manual Repairs & Maintenance

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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.

5.2.9DIODES : 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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Contents BK Precision Limited Two Year Warranty Table of Contents Section General Information Description Output ON/OFF SwitchLimit Setting Remote Programming With External 5K PotSection Specifications Section Installation Input TAP Selection for 230V Operation Repackaging for ShipmentSection Operating Instructions Readjust the current limit in the remote sensing mode Reverse Current Loading Output CapacitanceReverse Voltage Loading Terms in this Manual Terms AS Marked on Equipment Operators Safety SummaryUSE the Proper Power Cord Do not Service Alone Servicing Safety SummaryFor Qualified Service Personnel only USE Care When Servicing with Power onServicing shall be done only by Qualified personnel Section Service Instruction GeneralTrouble Shooting Techniques Repairs & Maintenance Page REF. PCB no PIN no Parts Ordering & ReplacingPage Page Fuse Blows Fault Finding ProcedureFuse Blows Unregulated O/P Voltage Unregulated O/P VoltageNo Output Voltage No O/P VoltageNo DPM Indication No DPM IndicationDPM not Read Unit not Take Current Unit not Take CurrentUnit Directly Goes to CC Unit Directly Goes To CCNo Current Control No Current ControlPoor Line Regulation Poor Line RegulationPoor Load Regulation Poor Load RegulationCV, CC, LED not Glow External Programming Not OK External Programming not OKRemote Sense not OK 1KPF/100V, Disc Section Part List & SchematicsL1791-FP-CNT-0603 PCB Assy 2P2W SW Push ButtonSW1 Grey Colour CAP for Push Switch SW2 SW3 PS-PREG-1791-0503 PCB AsslyDPM/01 REV 01 X PS-AUX-DC-L1791-0503 PCB Assly PS-PWR-L1791-0703A PCB AsslyBack Trough Assly Front Panel AsslyMain Chassis Assly Front Panel Layout Back Panel Layout TOP View Bottom View of Model 1790 Front Panel Control PCB of 1790 Power Module PCB of 1790 PRE Regulator / AUX. P/S PCBs 1790 Service Information Precision CorpPrecision Corp