Electronic repair facility uses computerised digital scanner for cost effective fault finding
June 2000
Maintenance, Test & Measurement, Calibration
Electrotest
The fault locator provides a fast and efficient means of testing electronic components, either in isolation or in circuit. Electrotest is able to locate faults in circuits by utilising the following methods:
1. Good board/bad board comparison - a working and faulty circuit are compared by scanning the exact point or chip on each PCB to each other. Should there be a deviation between the two scans, the technician is alerted and the suspect component is changed.
2. Good board "learning" - a working PCB is scanned or "learned" and saved to disk. When the PCB is returned to our workshops for repair, the saved scan is used to compare against the faulty PCB.
3. In circuit test - component functionality is tested with the component in circuit. This method is efficient and reduces the risk of damaging components, tracks and pads when removing it from the board to be tested in a remote digital tester.
The system Electrotest's workshops utilise, combines two powerful fault-finding techniques - analog signature analysis and in circuit testing. These two methods are expanded on below.
Analog signature analysis
Using the analog signature analysis method, safe, low power drive voltages are applied to components to produce an "impedance signature" on the PC screen. All testing is done with power disconnected from the circuit so there is no risk to the user and components under test cannot be damaged.
Good device signature can be rapidly digitised, viewed and stored in the hard disk of the host computer and printed out as hard copy. The locator can automatically compare signatures of suspect devices with the reference signatures stored on disk and print out test results and good and bad signatures for comparison.
In circuit testing
Using in circuit testing (ICT) the scanner compares the logical function of a device under test with a model of the corresponding device in its component database. The scanner is able to "learn" the operation of a device in circuit and use that configuration as a reference. Logical high and low "guard" voltages are provided on the unit front panel to enable isolation of bus-connected devices.
The ICT software is able to detect and display connected pins and to display a logic-timing diagram showing the status of the pins during testing.
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