The PCB shown in Fig. 1 is part of a medical diagnostic imaging system. It is placed on a receiving test panel connected to the microprocessor based controller and power supply via a fiber optic cable and a 24V power connector, Fig. 1.
Figure 1: Block diagram of the overall system
The processor and power supply each consists of several PCBs and is regarded as systems. The fiber optic cable transfers data, and the 24V connector supplies power to the receiving test panel.
The board (DUT) is covered before testing. The processor is connected to the computer system via a serial cable and Ethernet connector. The power supply gets AC power and supplies 5V power to the CP via a power cable.
Firmware is developed based on testing requirements using a higher-level computer language like C, Perl, AutoITScript, or Java. The firmware sends commands from the computer to the controller and from there to the receiving test panel to check if certain specs on the board (DUT) are met or failed.
Figure 2: The board is tested as part of the whole system
First, critical voltages need to be verified on the board (DUT) before putting it on the receptor test panel. Then communication software is used to check if proper booting up of the board occurs. This ensures that system is working and all the cables and wires are hookups are accurate.
For this particular board, the test development team produced a particular type of software to check the imaging of the overall system. Tests are performed to make sure that the image looks acceptable.
Figure 3 – Example of good dark image
A board image can fail for various reasons. For example, those can be one or more bad critical voltages, defective component on a particular test channel, dysfunctional oscillation from crystal chip, among others. Thorough component level diagnostics must be done to determine the cause of the failure, which often can be a result of defective or wrong or disoriented IC, capacitor, voltage converter, filter, among others.
Figure 4 – Example of bad image related to power supply problem
If a good dark image is found during test, further tests are performed on the board. Each different test is developed to find out how the board will actually perform with the overall imaging system in an actual real life application.