Dell Latitude LM Reference and Troubleshooting Guide - Page 70

fault by moving the program to another computer and running it there.) • The computer halts in the middle of performing cal- culations or complex mathematical operations. Subtests The subtests that constitute the System Set Test Group and the computer functions they confirm follow: • CMOS Confidence Test Checks the nonvolatile RAM (NVRAM) for accessibility and reliability of data storage by performing a data pattern check and verifying the uniqueness of memory addresses. • DMA Controller Test Tests the direct memory access (DMA) controller and verifies the correct operation of its page and channel registers by writing patterns to the registers. • Real-Time Clock Test Confirms the functionality and accuracy of the computer's real-time clock (RTC). • System Speaker Test Checks the functionality of the speaker by generating eight tones. • Secondary Cache Test Confirms the functionality of the secondary (external) cache on the system board. • System Timers Test Checks the timers used by the microprocessor for event counting, frequency generation, and other functions. Only the functions that can be activated by software are tested. • Interrupt Controller Test Generates an interrupt on each interrupt request (IRQ) line to verify that devices using that line can communicate with the microprocessor and that the interrupt controller sends the correct memory addresses to the microprocessor. • Coprocessor Calculation Test Checks the use of different types of numbers and the math coprocessor's ability to calculate correctly. • Coprocessor Duty Cycle Test Tests the math coprocessor's ability to perform complex mathematical operations. • Coprocessor Error Exception Test Verifies the math coprocessor's ability to handle errors and to send IRQs to the microprocessor. • PC Card Controller Test Checks the functionality of the PC Card controller on the system board. • Thermal Control Test Checks the functionality of the thermal-monitoring and microprocessor speed-switching device on the system board. This test does not apply to the Dell Latitude LM. Video Test Group The subtests in the Video Test Group verify the proper operation of the video controller and the video control circuitry installed in the computer. These subtests check for the correct operation of the readable registers in the video circuitry and the controller. They write, read, and verify data patterns in the cursor registers of the controller. The Video Test Group also provides additional subtests to test the color features of the color display or an external color monitor. Why Run a Video Test? Many of the symptoms that would prompt you to run a subtest in the Video Test Group are obvious, because the display is the visual component of the computer. Before you run the Video Test Group or any of its subtests, you should make sure that the problem is not occurring in the software or caused by a hardware change. If the following symptoms still occur, run the appropriate test(s) as follows: • If your display or external monitor shows a partially formed or distorted image, run all of the subtests in the Video Test Group. • If the alignment of text or images is off, regardless of the program you are running, run the Text Mode 4-14 Dell Latitude LM Reference and Troubleshooting Guide