A+ (2006-07) / Lessons

Fault-Finding

Common Faults

Power Supply Problems

The PSU is connected to virtually every other component — if it fails, it can affect the whole system.  Typical symptoms include:

Checking a 'Dead' System

Visually inspect, checking for unseated cards, loose cables or foreign objects.

  1. Check that the power cable is plugged into a functioning mains outlet.
  2. Check the position of the on / off switch.
  3. Examine the power cord for good connection at the rear of the unit.
  4. Check the setting of the 110 / 230 switch setting on the outside of the power supply.  This should be 110V in the US and 230V in the UK.
  5. Check the mains voltage by plugging other mains equipment into the outlet.  Alternatively use an electrician's screwdriver or a multimeter.
  6. Use a multimeter to check motherboard & disk drive connector voltages.

If the PSU is not the cause, one of the other components must be overloading the supply.  Uninstall components one-at-a-time to identify the cause.

Remember: with the power button off, there may still be some levels of voltages applied to the system board.  Turn off all system power before removing parts!

Common fault: A short-circuit inside a hard drive can force the PSU into fail-safe 'off' mode.  Therefore, when testing a PSU be sure to unplug hard drive power connectors.

Common fault: A faulty motherboard can fail to signal an ATX supply to power-up, but a PSU MUST have some kind of an electrical load (e.g. the motherboard) when being tested.

Active lights and spinning fans mean that at least some portion of the PSU is functional.  There are two likely possibilities:

Check the supply by substitution with a known-working PSU.  By elimination, if the cause is not the PSU then something else must be overloading the PSU.

Common fault: the CPU fan spins once or twice and then stops.  The PSU is switching on and then overloading.  Usually indicates a faulty PSU, and should be checked by swapping-in a known-working PSU.

System Board Troubleshooting

Observe the boot up and operation.  What steps lead to the failure?  Note any error messages / beep codes.  Refer to the motherboard user manual to check for hardware configuration problems.  If possible, run software diagnostics.

Configuration Checks

If the battery fails, or has been changed, the contents of the CMOS will be lost.  After replacing the battery, it is always necessary to reconfigure the CMOS setup.  (If the motherboard has been recently removed, CMOS pins may have inadvertently been short-circuited by anti-static measures.  CMOS should always be checked after installing a system board.)

RAM

If software diagnostics are unavailable, use logical rotation (swapping) of the RAM modules to locate a defective RAM module.

The first is soft-memory errors are caused by infrequent and random glitches in the operation of applications and the system.  You can clear these events just by restarting the system.  Hard-memory errors are permanent physical failures.

Mixing RAM types / speeds can cause the system to lock up and give errors.

Processor

If the CPU is faulty the speaker may issue a slow, single beep, with no display or other I/O operation.  If the system consistently locks up after a few minutes, this is a good indication that some heat build-up problem is occurring.

Troubleshooting Video

If the screen flickers upon entering Windows, reboot and press F8 when the "Starting Windows" message appears, and select Safe Mode.  This should load Windows with the standard 640×480×16-color VGA driver, which nearly all monitors support.

Troubleshooting Monitors

The first step in isolating the monitor as the cause of the problem is to exchange it for a known good one.  If the replacement works, the problem must be located in the monitor.  Refer the monitor to qualified technicians.

Troubleshooting Floppy Disk Drives

Activity light stays on constantly — means the signal cable is reversed.

Check for foreign objects, e.g. a dust cover that may have fallen off a disk.

Troubleshooting Hard Disk Drives

If the configuration information is correct and you suspect a hard disk drive problem, the first task is to determine how extensive the problem is.

Check the signal cable for proper connection at both ends.  Exchange the signal cable(s) for a known good one.  Check the Master/Slave/CS jumper settings.  Exchange the HDD power connector with another one from the power supply, to make certain that it is not a source of problems.

Windows NT / 2000 / XP / Server 2003 boot failures

If the main partition is NTFS-formatted then it cannot be read using MS-DOS or Windows 9x boot floppies.  Instead, you should use a bootable CD such as Windows PE or Bart PE, or use the Windows 2000 / XP Recovery Console.  To correct the master boot record, use FIXMBR.

http://www.bootdisk.com/ contains handy hints on how to fix boot problems and how to create bootable CDs.

CD-ROM Drives

The steps for a CD-ROM drive are almost identical to those of an HDD.

In addition, check for simple user problems.  Is there a CD in the drive? Is the label side of the disk facing upward?  If there is a CD locked inside, insert a straightened paper clip into the tray-release access hole.

USB Port Checks

Check the CMOS to make sure that the USB function is enabled there.  If the USB function is enabled in BIOS, check in the Windows Control Panel > System > Device Manager to check that the USB controller appears there.  If a USB device does not install itself automatically, you may have conflicting drivers loaded for that device and you may need to remove them.

Fault-finding technique

Rule 1 — Visual inspection

Carry out a visual inspection looking for obvious signs of problems:

Poorly-seated connectors or expansion cards

Loose connectors (but some connectors are meant to be loose!)

Foreign objects — for example loose screws

Physical damage

Motherboard power connector incorrectly aligned

Rule 2 — Methodical testing

Operation of the PC can be broken down into three stages:

Power

The clearest sign of a power problem is when the power supply fan fails to spin.  If the fan is spinning then main power must be available.

If the CPU fan fails to spin then there may be a fault with the power supply's output.  Check the power connector voltages with a voltmeter.

Core system

A PC requires only three parts for basic operation: a CPU, motherboard and RAM.  We'll also need a graphics card so we can see whether the core system is working.

If the core system fails then we should resort to testing each part individually by swapping with similar parts in a known-working computer.

The BIOS can produce patterns of beeps on a speaker that identify common faults (such as no video card or memory error).  These are known as POST (Power On Self-Test) codes.

Extras

If the core system works, plug in extra components one at a time, testing each for full functionality before continuing.  It is recommended that you test the floppy drive first: this will give you access to disk utilities when testing hard drives.  It is then recommended that you test the hard disk drive.  If you can install a working operating system then this will allow you to test other devices such as CD-ROMs, sound cards and network cards properly.