Troubleshooting Equipment Containing Integrated Circuits Jimmie Fouts Houston County Career Academy

Key to Troubleshooting! Troubleshooting equipment with integrated circuits is essentially the same as any other equipment The key is to have a good overall block diagram of the equipment Failure symptoms can often be localized by reviewing the functions of stages within the equipment

Equipment Service Literature Most equipment manufacturers provide servicing literature to assist in troubleshooting their equipment Refer to the steps contained in this literature for test procedures

Check for Power Supply Operation! Integrated circuits are generally very reliable One of the most common faults in equipments containing IC’s is the dc power supply If no dc power exists, check the ac supply to the power supply

Use Block Diagram! Equipment block diagrams often contain test point information The block diagrams also often contain input and output waveforms between stages Using the DMM to measure voltage and oscilloscope to view waveforms, attempt to isolate the failure to a specific stage

Obtain the IC Pin Diagram Once a stage is identified, the isolation of the defective integrated circuit is often a relatively easy operation! Obtain the IC pin diagram from the service literature or from the IC manufacturer Specification Sheets The pin diagram will identify what to expect on the pins of the IC

Verify IC Operation Once the stage has been identified, IC’s within the stage can be tested This operation is generally accomplished by checking voltages and waveforms on the pins of the IC If inputs are correct and outputs are measured as incorrect, the logical conclusion is that the IC has failed

Important Notice Always check for proper supply voltages first! Improper supply voltages will affect IC operation in most cases Be aware that circuit operation of the stage following the IC may affect the output of the IC under test ◦For example: If the following stage presents a short circuit to the IC under test, the current IC will show no output

Other Observable Conditions Before replacing IC’s, look for signs of overheating ◦Discolored components or top of IC ◦Burned or charred components ◦Discolored circuit board Look for signs of poor solder joints ◦Poor solder joints are indicated by cracks or discoloration of the solder joint

IC Sockets Don’t overlook problems with the IC socket holding the IC in the circuit Often IC sockets are used to allow for the easy removal and replacement of defective IC’s Overtime smoke, dust, dirt, and corrosion of the socket contacts can lead to equipment failure Poor contact with IC leads can result in failure!

Replacing IC’s When replacing IC’s: ◦If used, clean the IC socket with appropriate solvent, vacuum, or air as appropriate ◦Ensure the use of the correct IC ◦Ensure the correct placement of IC pins into the circuit ◦Verify power supply voltage at the IC pins before assuming that equipment operation is normal ◦Verify proper operation of any fans or cooling units in the equipment

When No IC Socket is Used IC replacement is generally more difficult when no socket has been used. Use appropriate desoldering equipment! Surface mount IC’s often require the use of hot air rather than a soldering iron/suction often used for thru-hole mounting Avoid the use of excessive heat which can damage the circuit board and other components Use proper tools!

IC Replacement Ensure power is OFF before removing or replacing integrated circuits Ensure proper alignment of the pins to the mount Avoid handling the IC using the pins ◦IC’s are often sensitive to high static charge ◦Discharge hands by touching the equipment ◦Handle IC’s by their case and only when necessary

IC Identification Every manufacturer uses unique part numbers to identify IC’s Number systems may include numbers, prefixes, logos, and suffixes. Substitution guides, vendor catalogs, and IC data books can help in IC identification An example: LF356CN/A+ ◦LF = linear family (BIFET) ◦356 = part number ◦C = temperature range for commercial use ◦N = Package type – dual in-line epoxy ◦A+ = high reliability revision