Computer Hardware Trouble Shooting or

The computer won’t work!!! – Now what am I going to do?

Basic steps for diagnosing computer problems:

1. Look and listen – the computer will give you some hints about what is wrong with it – usually in lights, sounds or messages on the monitor screen

Example: Turn on the computer a) Are there any case lights? – possible power supply problem (did you plug it in?) b) Is there any sounds coming from the case (case fans whirring, etc.) – if not – possible

power supply problem c) Are there case lights and a fan turning, but no beeping – usually a bad CPU that needs

replacing. d) Is the computer beeping? If it is – then it’s trying to tell you what’s wrong e) Is there a message on the monitor screen? This means that the CPU, RAM and video

card are working – a possible problem with the hard drive (HDD Controller error – a change in hard disk parameters) or the floppy drive.

f) Consult the flowchart ( PC repair poster.pdf) 2. Common BIOS beep codes (case lights and fan movement present):

a) No beep – possibly a bad CPU or RAM short b) 1 beep – GOOD – everything is working c) 1 long constant beep – RAM error – make sure it is seated well d) 1 long – 3 short – Video card error – make sure it is seated, or replace the defective card. e) 2 short – usually means a change in the system BIOS

When a computer starts, it goes through the following sequence during power-up Power supply, CPU, RAM, Video, floppy drive, hard disk. We need to know this to test the machine if there is power, but no beeping. Take out all parts and add to get beeps. Example – power supply + CPU should give a RAM error – if not we have a dead CPU. If we get a RAM error then add RAM – should get a video error – no? = RAM short. If there is video, then there likely is a short in one of the peripheral cards (sound, network, etc – insert one at a time to see the problem) or the HDD cable might be on backwards (will short some motherboards) More BIOS beep codes are listed on the following pages for usual makes of computers.

BIOS Beep Codes

What is a BIOS Beep Code? When you power on a computer the BIOS immediately takes control of the computer and performs the P.O.S.T (Power On Self Test). At the end of the POST the computer will play an audible 'BEEP' through either the PC's internal speaker of through speakers attached to the sound card (if you have a built-in sound chip). If the POST completed successfully without detecting any problems with then system will play a single short beep to let you know the test is complete and the computer will continue to start up and load the operating system.

If during the POST the BIOS detects a problem it will normally display a visual error message on the monitor explaining what the problem is. However, if a problem is detected before the BIOS initializes the video card, or a video card is not present or not detected then the BIOS will play several 'BEEPS' through the speaker to let you know there is a problem. Depending on the type of the BIOS you have the BIOS may play beeps in a specific pattern to indicate what the problem is, or play the same beep a number of times indicating the problem. It is very important that you pay close attention to the number and/or pattern of the beeps your computer plays on startup.

Below is a table of the most common AMI, Phoenix, Award, Compaq Dell and IBM BIOS beep codes. AMI (American Megatrends International) BIOS Beep Codes. AMI BIOS uses beeps of the same length and pitch. The error is displayed as a number of beeps. For example, 4 beeps indicated a timer failure. BEEP CODE MEANING POSSIBLE CAUSE 1 Beep (No video) Memory refresh failure Bad memory 2 Beeps Memory parity error Bad memory 3 Beeps Base 64K mem failure Bad memory 4 Beeps Timer not operational Bad motherboard 5 Beeps Processor error Bad processor 6 Beeps 8042 Gate A20 failure Bad CPU or Motherboard 7 Beeps Processor exception Bad processor 8 Beeps Video memory error Bad video card or memory 9 Beeps ROM checksum error Bad BIOS 10 Beeps CMOS checksum error Bad motherboard 11 Beeps Cache memory bad Bad CPU or motherboard Award BIOS Beep Codes Award BIOS uses beeps of varying duration. A long beep will typically last for 2 seconds while a short beep will last only 1 second. Award BIOS also uses beeps of different frequency to indicate critical errors. If an Award BIOS detects that the CPU is overheating it may play a high pitched repeating beep while the computer is running. BEEP CODE MEANING POSSIBLE CAUSE 1 Long, 2 Short Video adapter failure Bad video adapter Repeating (Endless loop) Memory error Bad memory or bad connection 1 Long, 3 Short Video adapter failure Bad video adapter or memory High freq. beeps (while running) CPU is overheating CPU fan failure Repeating High, Low beeps CPU failure Bad processor

Phoenix BIOS Beep Codes Phoenix BIOS uses beep code patterns to indicate problems. In the table below the '-' indicates a brief pause between beeps. Example: 1 - 1 - 2 would sound like BEEP <pause> BEEP <pause> BEEP BEEP BEEP CODE MEANING POSSIBLE CAUSE 1 - 1 - 2 CPU / motherboard failure Bad CPU / motherboard 1 - 1 - 3 CMOS read/write failure Bad motherboard 1 - 1 - 4 BIOS ROM failure Bad BIOS chip 1 - 2 - 1 Timer failure Bad motherboard 1 - 2 - 2 DMA failure Bad motherboard 1 - 2 - 3 DMA failure Bad motherboard 1 - 3 - 1 Memory refresh failure Bad memory 1 - 3 - 2 64K memory failure Bad memory 1 - 3 - 3 64K memory failure Bad memory 1 - 3 - 4 64K memory failure Bad memory 1 - 4 - 1 Address line failure Bad memory 1 - 4 - 2 Parity error Bad memory 1 - 4 - 3 Timer failure Bad motherboard 1 - 4 - 4 NMI port failure Bad motherboard 2 - 1 - 1 64K memory failure Bad memory 2 - 1 - 2 64K memory failure Bad memory 2 - 1 - 3 64K memory failure Bad memory 2 - 1 - 4 64K memory failure Bad memory 2 - 2 - 1 64K memory failure Bad memory 2 - 2 - 2 64K memory failure Bad memory 2 - 2 - 3 64K memory failure Bad memory 2 - 2 - 4 64K memory failure Bad memory 2 - 3 - 1 64K memory failure Bad memory 2 - 3 - 2 64K memory failure Bad memory 2 - 3 - 3 64K memory failure Bad memory 2 - 3 - 4 64K memory failure Bad memory 2 - 4 - 1 64K memory failure Bad memory 2 - 4 - 2 64K memory failure Bad memory 2 - 4 - 4 64K memory failure Bad memory 2 - 4 - 4 64K memory failure Bad memory 3 - 1 - 1 Slave DMA failure Bad motherboard 3 - 1 - 2 Master DMA failure Bad motherboard 3 - 1 - 3 Interrupt controller failure Bad motherboard 3 - 1 -4 Slave IC failure Bad motherboard 3 - 2 -2 Interrupt Controller failure Bad motherboard 3 - 2 - 3 <RESERVED> 3 - 2 - 4 Keyboard control failure Bad motherboard 3 - 3 - 1 CMOS batter failure Bad CMOS battery 3 - 3 - 2 CMOS configuration error Incorrect setting 3 - 3 - 3 <RESERVED> 3 - 3 - 4 Video memory failure Bad video card or memory 3 - 4 - 1 Video init failure Bad video card or memory 4 - 2 - 1 Timer failure Bad motherboard 4 - 2 - 2 CMOS shutdown failure Bad motherboard 4 - 2 - 3 Gate A20 failure Bad motherboard 4 - 2 - 4 Unexpected interrupt Bad processor 4 - 3 - 1 RAM test failure Bad memory 4 - 3 - 3 Timer failure Bad motherboard 4 - 3 - 4 RTC failure Bad motherboard 4 - 4 - 1 Serial port failure Bad motherboard 4 - 4 - 2 Parallel port failure Bad motherboard 4 - 4 - 3 Coprocessor failure Bad motherboard or CPU. 9 - 2 - 1 Video adapter incompatibility Use a different brand of video card

Compaq BIOS Beep Codes: - difficult since most models have different beep codes

Beeps Error Message Description 1 short No error System is booting properly 1 long, 1 short BIOS ROM checksum error The contents of the BIOS ROM to not match the expected

contents. If possible, reload the BIOS from the PAQ 2 short General error Unknown 1 long, 2 short Video error Check the video adapter and ensure it's seated properly. If

possible, replace the video adapter 7 beeps (1 long, 1s, 1l, 1 short, pause, 1 long, 1 short, 1 short

AGP video The AGP video card is faulty. Reseat the card or replace it outright. This beep pertains to Compaq Deskpro systems

1 long neverending beep

Memory error. Bad RAM. Replace and test

1 short, 2 long Bad RAM Reseat RAM then retest; replace RAM if failure continues

Dell BIOS Beep Codes:

Beep Codes Possible Causes Corrective Action 1 - 2 No video card detected Reseat the video card 1 - 2 - 2 - 3 BIOS ROM checksum error 1 - 3 - 1 - 1 DRAM refresh error Reseat the memory modules 1 - 3 - 1 - 3 8742 Keyboard Controller error Reseat the keyboard connector 1 - 3 - 3 - 1 Memory defective or not present Reseat the memory modules 1 - 3 - 4 - 1 RAM failure on line xxx Reseat the memory modules

1 - 3 - 4 - 3 RAM failure on data bits xxx of low byte on memory bus Reseat the memory modules

1 - 4 - 1 - 1 RAM failure on data bits xxx of high byte on memory bus Reseat the memory modules

IBM BIOS beep codes

Below are IBM BIOS Beep codes that can occur. However, because of the wide variety of models shipping with this BIOS, the beep codes may vary.

Beep Code Description No Beeps No Power, Loose Card, or Short. 1 Short Beep Normal POST, computer is ok. 2 Short Beep POST error, review screen for error code. Continuous Beep No Power, Loose Card, or Short. Repeating Short Beep No Power, Loose Card, or Short. One Long and one Short Beep Motherboard issue. One Long and Two Short Beeps Video (Mono/CGA Display Circuitry) issue. One Long and Three Short Beeps. Video (EGA) Display Circuitry. Three Long Beeps Keyboard / Keyboard card error. One Beep, Blank or Incorrect Display Video Display Circuitry.

CPU Installation: If you have a defective CPU, replacement is easy if you have another identical CPU. Make sure that you are grounded and insert it (make sure you don’t bend any pins). There is only one way that a CPU can fit on the motherboard. If you don’t have the identical speed CPU, you can insert another as long as it has the same number of pins and an identical BUS (data transfer – usually 66 Mhz, 100 Mhs, 133 Mhz, 200 Mhz) speed to match the motherboard. There is usually a chart on the motherboard with jumper settings for the various BUS speeds and multipliers (1X, 1.5X, 2X, 2.5X, 3X, …, 15X) Let’s say you have a 450 Mhz Pentium 3 that needs a new CPU. Problem is – you have an extra 600 Mhz CPU to use. A 450 Mhz CPU has a BUS speed of 100 Mhz. (450 = 100 mhz X 4.5) You would see the jumpers set for this in the chart on the motherboard (100 Mhz BUS and a 4.5 multiplier). To set the system to use the 600 Mhz CPU, you would have to re-set the jumpers to the same 100 Mhz BUS, but the multiplier would be 6. Start the machine and you’ll see the new CPU setting in the first screens that computer shows you at start-up In older machines (Pentium 1 and Pentium 2), the BUS and multiplier combinations were already made for you in the chart. You just had to find the correct one – BUT – you have to make sure that PCI speed was set to 33 Mhz or else your video card, modem, soundcard or network card might work incorrectly. Over-clocking a Computer: Most CPUs have an overhead of speed. A 500 Mhz CPU might have been a 600 Mhz that didn’t test well in the factory and was “down graded” and marked as such. Many Pentium 2 motherboards have various different BUS speeds that can be used with CPUs to get more speed from the system. (see chart)

BUS (Mhz) Multiplier V-Core (Volts) 66 2X 1.65 (newer) 75 2.5X 1.7 85 3X 1.75 93 3.5X 1.8 (older P2) 100 4X 1.85 105 4.5X 1.9 110 5X 1.95 115 5.5X 2.0 120 6X 133 6.5X 7X 7.5X etc

Example – 300 Mhz (100 Mhz X 3) machine Try 105 Mhz X 3 = 315 Mhz and restart the machine. If the computer POSTs and runs the operating system - all is well. Keep using combinations of BUS and multiplier to get more speed (like 93 X 4 = 325.5, 110 X 3 =330, 85 X 4 = 340 etc) until the machine won’t work and then set it back to the last known working configuration. Now – add a bit more V-Core voltage (ie 1.8 volts to 1.85) and restart the machine to make sure it works. Start going up further until the machine stops again. Repeat as above, but set V-Core from 1.85 volts to 1.9 volts. Try again. Once you get as high as possible, run the machine for a while to make sure that it is stable. Over-clocking will cause more heat so good CPU cooling is needed. We have taken a 300 Mhz Celeron (model 300A with a 66 Mhz BUS) and over-clocked it to 540 Mhz. My students like to use this as a competition to see how fast they can make a machine operate. A good benchmark software is SysSoft Sandra. If a CPU doesn’t over-clock well, it may not have the speed overhead (a 300 was a 300).