Troubleshooting Troubleshooting Equipment Containing Equipment Containing

Integrated CircuitsIntegrated Circuits

Jimmie FoutsHouston County Career Academy

Key to Troubleshooting!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 LiteratureEquipment 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!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!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 DiagramObtain 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 OperationVerify 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 NoticeImportant 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 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 SocketsIC 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’sReplacing 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 UsedWhen 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 ReplacementIC 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 IdentificationIC 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