Symptom 1. The system is completely dead but the power LED is lit. If the system does not run any POST diagnostics, nor does it boot to run any third-party diagnostics, first use a multimeter to check the power supply outputs very carefully. Even though the power LED is lit, one or more of the outputs might be low, or absent. Excessively low outputs can easily result in logic errors that can freeze or lock up the system. If this condition began after adding an upgrade then the power supply may be overloaded-try removing the upgrade. If system operation returns then consider upgrading the power supply. If an output is low or absent and there has been no upgrade, try replacing the power supply. Next, strip the system of its peripherals and expansion boards, then try the system again. If operation returns, then one of the expansion devices is interrupting the system operation. Re-install one device at a time and check the system, the last device to be installed when the system fails is the culprit. Replace the defective device. If the failure persists, then replace the CPU. Remember to shut down and unplug the PC before removing the CPU and, also observe all standard anti-static procedures when handling the CPU. Be very careful not to bend any of the pins, as you may want to re-install the CPU later. Use care when installing the new CPU as bent pins will almost always ruin the IC. If a new CPU fails to correct the problem, then replace the motherboard outright.
If a CPU fault is indicated during the POST (initial BOOT) Check each output from the system power supply. If one or more outputs is low or absent, then there may be a problem with the power supply. Try a new supply. If all outputs measure properly then try a new CPU. If a new CPU fails to correct the problem then replace the motherboard outright. Symptom 3. The system boots with no problem, but crashes or freezes when certain applications are run. Try a diagnostic software program such as AMIDAIG from AMI or The troubleshooter by ALLMicro. Run repetitive tests on the CPU. Although the CPU might work in real-mode, diagnostics can detect errors running protected-mode instructions and perform through register checking. When an error code is returned suggesting a CPU fault, try another CPU. If a CPU fault is not detected, expand the diagnostic to test other portions of the motherboard. If the entire system checks properly then you probably have a corrupt file in your application. HEAT PROBLEMS Symptom 1. The system boots with no problem but crashes or freezes after several minutes of operation (regardless of the application being run) Also you will probably note that no diagnostic indicates a CPU problem. If you shut the system off and wait a few minutes, the system will boot fine and then run for several more minutes before stopping again-this is typical of thermal failure. When the system halts, check the CPU for heat (use extreme caution when checking for heat, you can easily be burned) If the CPU is not fitted with a heatsink, make sure the system cooling fan is working and that there is an unobstructed path over the CPU. If not consider applying a heatsink with a generous amount of thermal compound. If the CPU is fitted with a heatsink and abnormal heat is detected then make sure there is an ample layer of thermal (heatsink) compound between the CPU case and the heatsink base. In many cases the compound is omitted. This ruins the transfer of heat and allows the CPU to run much hotter. If you find there is no thermal compound, allow the CPU to cool, then add thermal compound between the CPU case and heatsink. Also if this start-freeze-stop-start behavior occurs after you have recently installed a new motherboard or CPU, and heat is not the problem then make sure that the system clock jumpers have been correctly enabled. An incorrect clock jumper setting will cause similar intermittent behavior. |
