Mainboard Startup Diagnostics
Modern mainboards have a startup diagnostic, the so called "Power ON Self Test" (POST). This means they check themselves for the availability of the vital functions, the memory and some of the slot cards. In order to be able to run the diagnostics the following prerequisits have to be fullfilled:
- The power supply has o generate the correct voltages and set the POWER OK signal. This is not true if e.g. the power supply detected a shortage on one of the voltages (which could caused by the mainboard or one of the drives).
- The CPU has to be able to come out of the reset condition and has to be able to execute processor instructions.
- The BIOS chip has to be present on the mainboard and has to be readable for the CPU.
- The BIOS chip has to contain a valid program. This will be checked via a checksum.
- The CMOS has to be present and readable for the CPU.
- The CMOS has to contain valid data. This is checked via a checksum. In case of doubt the CMOS can be cleared by setting a jumper on the mainboard. It will be brought into a defined condition by this.
- The CPU has to be able to access the memory (RAM). This means that the memory controller, memory bus and memory modules have to be o.k.
- The first 64KB (KiloByte) of memory have to be o.k. to be able to store the POST data. In case of doubt the memory should be replaced by another module (e.g. swap the memory modules among each other).
- The I/O bus (I/O Controller) has to be o.k.
- The CPU has to be able to access the graphic adapter via the I/O bus to read and write data.
- The graphic adapter has to be present and has to be o.k. (video chip and video memory).
- The loudspeaker / beeper has to be connected correctly and has to be o.k.
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These functions have to be o.k. to execute the basic POST tests. E.g. if the memory or the graphic adapter is not present or not o.k. the system may output a beep code via the loudspeaker to notify of the defect. This is however not possible for all errors. Also the tests do not necssarily run in the above sequence. However, the good results of the tests are the prerequisites to run the higher tests as e.g. floppy disk and hard disk checks.
The cache memory controller usually will be only activated after a successful starup diagnostic. Therefore it is unlikely that cache problems will be detected by the startup diagnostics.
In the following section some beep codes are listed which are output by the mainboard checks in case of a detected error. This is, as it was already mentioned, if the system is not able to start up as far as to be able to output an error message via the graphic adapter. Also note that errors which generate a beep code can never be generated by operating systes or software.
AMI BIOS
| 1 beep
|
DRAM refresh failure |
| 2 beeps
|
Parity Circuit Failure |
| 3 beeps
|
Base 64K RAM failure |
| 4 beeps
|
System Timer Failure |
| 5 beeps
|
Processor Failure |
| 6 beeps
|
Keyboard Controller / Gate A20 Failure |
| 7 beeps
|
Virtual Mode Exception Error |
| 8 beeps
|
Display Memory Read/Write Failure |
| 9 beeps
|
ROM BIOS Checksum Failure |
| 10 beeps
|
CMOS Shutdown Register Read/Write Error |
At 1 beep, 2 beeps, or 3 beeps it is recommendable to remove the memory (RAM) and reseat it to take care of pssible contact problems. If this does not help the memory should be replaced by a module which is definitely o.k.
At 4 beeps, 5 beeps, 7 beeps, or 10 beeps most likely the mainboard is defective.
At 6 beeps most likely the keyboard or the keyboard controller is defective. Try another keyboard and if this doesn't help the keyboard cotroller or mainboard has to be replaced.
At 8 beeps most likely the graphic adapter is defective and has to be replaced. But first try to reseat it.
At 9 beeps the BIOS chip is defective. In most cases it can be preplaced. You can ask your mainboard manufacturer for a replacement.
Remark by Peter Götz: Often the problem is only a defective battery, or in older systems the
rechargable battery may be flat, if the PC was not used for some time.
Award BIOS
One long beep followed by 2 short beeps: shows that the graphic adapter is not seated correctly or is defective.
All other beeps: Most likely defective or mis-seated RAMs or defects no the mainboard.
Phoenix BIOS
| 1-1-3 |
CMOS write/read failure. |
| 1-1-4 |
BIOS ROM checksum error. |
| 1-2-1 |
System timer failure. (Programmable Interval Timer PIT) |
| 1-2-2 |
DMA (direct Memory Access) failure. |
| 1-2-3 |
DMA page register failure. |
| 1-3-? |
RAM failure. |
| 1-4-1 |
64K RAM address line failure. |
| 1-4-2 |
64K RAM parity error. |
| 2-?-? |
Any beep series starting with 2 beeps indicates a 64K RAM chip or data line error. |
| 3-1-1 |
Master DMA register test. |
| 3-1-2 |
Mslave DMA register failure. |
| 3-1-3 |
Master interrupt mask register failure. |
| 3-1-4 |
Slave interrupt mask register failure. |
| 3-2-4 |
Keyboard controller failure. |
| 3-3-4 |
Screen (video) memory failure. |
| 3-4-1 |
Screen initialization failure. |
| 3-4-2 |
Screen retrace failure. |
| 4-2-1 |
Timer tick interrupt test failure. |
| 4-2-2 |
Shutdown test failure. |
| 4-2-4 |
Unexpected interrupt in protected mode. |
| 4-3-1 |
RAM test failure above address 0FFFFh (64K +) |
| 4-3-3
|
Interval timer channel 2 test failure. |
| 4-3-4 |
Time of day clock failure. |
| 4-4-1
|
Serial port test failure. |
| 4-4-2 |
Parallel port test failure. |
| 4-4-3
|
Math Co-processor failure. |
The codes may differ strongly depending on the version of the BIOS. Therefore it is recommended to download the appopriate data sheets.
Still Problems?
ATTENTION! Before you unplug or replug slot cards or other components, you must always power down the PC and then unplug the power cord. In modern PCs the power supply will always supply the mainboard with a voltage. If you do not observe this, this may damage the mainboard or components. It also may endanger your life to touch the PC or it's components while the power cord is plugged in.
If you can not hear any beeps and the screen remains dark, check the following:
- Is the loudspeaker connected correctly?
- Is the screen connected correctly and switched on?
- The power supply should be checked. Connect the power LED to the appropriate pins on the mainboard (watch the polarity). If the LED is illuminated and the motors of the hard disk, etc. are running the power is usually o.k.
- Check the mainboard for loose or missing components. E.g. is the CPU seated correctly in the socket and the RAM modules placed correctly.
- Remove all I/O slot cards except the graphic adapterand check again if the system is starting. If this is the case plug back the cards one after the other to their original posistion. Check for every card if the system is able to start up. A defective card can drag the whole system down. If the system still does not run, either the mainboard or the RAM is defective.
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BIOS Information Pages
Phoenix BIOS codes - http://www.phoenix.com/pcuser/PDF-Files/bios-postcode.pdf as PDF files from Phoenix.
Phoenix BIOS codes - http://www.firmware.com/support/oldbios/1011.htm from Microfirmware.
FAQ pages for the Phoenix BIOS - http://www.phoenix.com/pcuser/BIOS/biosfaq2.htm
Manufacturer informations for the Award BIOS - http://www.phoenix.com/PlatSS/pcplatforms/desktop/awardbios.html and Phoenix BIOS
Manufacturer informations for the AMI BIOS - http://www.ami.com/amibios/
General BIOS information page - http://www.wimsbios.com from Wim.
Problems with Components?
If your computer system starts up, but something is still not working, you should consult these support pages. This si an excellent generalsupport page. (in English)
For problems which can be doubtless assigned to components, you should consult the support pages of the various manufaturers. Here you find handbooks, support, jumper settings, etc.:
Acer - http://global.acer.com/support/index.htm
Adaptec - http://www.adaptec.com/support
ALR - http://www.alr.com/service/service.htm
Apple - http://support.info.apple.com/manuals/manuals.qry
AST - http://www.ari-service.com/default.asp
AT&T/NCR - http://www.ncr.com/support
CalComp - http://www.calcomp.com/support.htm
Canon - http://www.ccsi.canon.com/care/index.html
C.ITOH/CIE - http://www.citoh.com/dnload.htm
Compaq - http://www.compaq.com/support
Comtrol - http://www.comtrol.com/techsup.htm
CTX - http://www.ctxcomputers.com/techsupport.html
Dataproducts - http://www.dpc.com/support/technote/tn_dir.html#B
DEC - http://ie.digital.com/channel/documentation/pcdoc
Dell - http://www.dell.com/support/index.htm
DTK Taiwan - http://www.dtk.com.tw/pc-sup/tech.html
Epson UK - http://www.epson.co.uk/support
Epson US - http://www.epson.com/support
Epson US FTP site - ftp://ftp.epson.com
Epson technical data - http://support.dell.com/oti/index.asp?cc=5
Everex - http://www.everex.com/support.html
Exabyte - http://www.exabyte.com/home/suppserv.html
Future Domain - http://www.adaptec.com/support/eol/index.html#hardware
Gateway 2000 - http://www.gw2k.com/frameset.asp?s=home&p=support
GCC Technologies - http://www.gcctech.com/ts/index.html
Hewlett Packard - http://www.hp.com/cposupport/eschome.html
IBM - http://domino.www.ibm.com/Support/wwsup30e.nsf/d81ba789eae09118802564ca00636d9a?OpenView
IBM FTP site - ftp://ftp.pc.ibm.com/pub/pccbbs
IBM PC Service manuals -http://www.pc.ibm.com/us/cdt/hmm.html
Intel - http://support.intel.com/sites/support/welcome.htm
Mannesman/Tally - http://sales.tally.com/tech/techserv.html
Micron - http://support.micronpc.com
Mitac - http://mitac.mic.com.tw/service/service_a.htm
NEC - http://support.neccsdeast.com
NCD - http://www.ncd.com/support/support.html
NCR/AT&T - http://www.ncr.com/support
Okidata - http://www.okidata.com/services/pub.html
Olivetti - http://www.ocwi.com/ihdesk/firstpag.htm
Printronix - http://www.printronix.com/html/ampc-sup/tech.html
Quantex - http://www.quantex.com/community/qmembers/support/aboutsup.asp
Samsung - http://samsungelectronics.com/nonjava/support/downloads/index.html
SATO USA - http://www.satoamerica.com/tech/pc-sup/tech.htm
Seikosha America - http://www.seikosha.com/printers.html
SGI - http://www.sgi.com/support/info.html
SONY - http://www.ita.sel.sony.com/support
Stallion Technologies - http://www.stallion.com/html/userdoc.html
Star Micronics - http://www.starmicronics.com/tech/index.cfm
Swan Technologies - http://support.neccsdeast.com/swan-zdsdirect/zds
Texas Instruments - http://www.genicom.com/techsupp/TI/TI-techspt.htm
Toshiba - http://www.toshiba.com/tais/csd/support
Trantor - http://www.adaptec.com/support/eol.html#hardware
Unisys - ftp://ftp.gcs.unisys.com/pub
Wangtek/WangDAT - http://www.tecmar.com/support/download/techdocs.html
Zenith Data Systems - http://support.neccsdeast.com/swan-zdsdirect/zds
ZEOS - http://www.micronpc.com/support/file_lib/zeosbbs/zeosbbs.html
Special Help for Display Problems can be found on these Pages (e.g. circuit diagrams):
Electronix - http://www.electronix.com/schematics
Anatek - http://www.anatekcorp.com
Problems with Software?
If you have problems with MicroSoft products, you can search http://support.microsoft.com/support/a.asp for support for special problems with certain products. This is a side entry to the MicroSoft support pages.
For "shutdown" problems with Windows 9x and ME you may find help on this page http://www.freespeech.org/Khephra/a/shutdown.htm.
