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COMPUTER BITS By JENNIFER BONNITCHA What to do when your computer goes bung; Pt.5 Why are motherboards called "motherboards"? It is because they have all those sockets into which "daughter boards" are plugged in, much like baby pigs suckling from the sow. But motherboards don't always lavish care and sustenance; they can be a source of trouble too. Since the motherboard is a large fibreglass sheet with connectors for the various plug-in cards, it is subject to stress and strain. As you add more cards, it tends to twist and flex, particularly in the less-well manufactured clones. On some cheap motherboards, inserting cards roughly can cause it to crack. That is the beginning of the end since the split becomes progressively worse until finally it breaks. Less obvious to detect is a nonfunctioning motherboard. Since nothing works, how can you eliminate suspect devices? If you think the motherboard could be at fault, check the following: • the power is actually switched on; • the power point works anyway; • all connectors are OK; • loose screws, etc on the motherboard, which could cause short circuiting; • correct system board settings as appropriate. After all that, you may need to call on your friendly technician for further help. Obviously, the amount of time you spend tinkering depends on your own capabilities. You should find the following voltages at the motherboard power connector [top left hand corner of photo): VOLTAGE PINS +4 .8 to 5 .2 +4.5 to 5.4 + 1 1.5 to 12.6 +10 .8 to 12 .9 P8-5 ; P9-3; P9-1; P8-4; P9-4 P8-6 P8-3 P9-2 What time is it? The internal rechargeable battery maintains the computer's real time clock. Just like the watch on your wrist, when the battery runs flat, the date and time are out. Replace the battery and all should be well. Occasionally, you may need to run your computer's diagnostic or setup procedure, even after using the DOS commands DATE and TIME. Typically, this will reset the real time, rather than the system time and so will remain in effect even when the computer is turned off. Common programs include TIMER, SETDATE, SETTIME and so on. Check your DOS manual for further information. A window to the world Monitors and video cards were discussed at some length in earlier articles but what do you do when they play up? There are a few things you can do to check the operation of your monitor: • Is the monitor actually turned on? Don't assume that since it usually comes on when the computer does, that it is broken in some way. Users not familiar with your computer's operation may have assumed that the monitor needs to be turned off separately to the system unit. Check. • For those monitors with integrated power cables, check tha.t the cable is securely attached to both the monitor and system unit. If it is, and the monitor power switch is on, try using a separate power cable, since there could be a problem with the outlet from the system unit. • Check the brightness and contrast controls if nothing appears on the screen. Someone may have turned them right down and forgotten about them, so that the monitor appears dead. Again, different users may have adjusted them to suit a particular program and the settings may be inappropriate for the program you wish to run. • Check that the monitor cable is securely attached to the system unit. Several cards can have lookalike sockets. Check that the monitor is connected correctly. • If possible, check the suspect monitor on another computer and a different monitor on your computer. The key to success is elimination. • If the monitor comes on but the program you want to run seems to do nothing, check the installation procedure. You need to make sure the program knows exactly what SEPTEMBER1990 93 Table 1: System Board Errors Table 4: Hard Disc Drives 101 1 02 1 03 1 04 1 05 Problems with the hard disc return the 1 7xx series of codes: System Board Error; Interrupt failure System Board Error; Timer failure System Board Error; Timer interrupt failure System Board Error; Protected mode failure System Board Error; Last 8042 command not accepted 1 06 System Board Error; Converting logic test 1 07 System Board Error; Hot Non Maskable Interrupt test 1 08 System Board Error; Memory select error 1 09 System Board Error; Memory select error 1 21 Unexpected hardware interrupts occurred 161 System Options Not Set - (Run SETUP); Dead battery 162 System Options Not Set - (Run SETUP); CMOS checksum/configuration error 163 Time & Date Not Set - (Run SETUP); Clock not updating 164 Memory Size Error - (Run SETUP); CMOS setting does not match memory Table 2: Keyboard Errors 301 Keyboard did not respond to software reset or a stuck key failure was detected. For stuck keys the key scan code displays in hexadecimal. 302 System Unit Keylock is locked 303 Keyboard or System Unit Error 304 Keyboard or. System Unit Error; Keyboard clock high The most likely reason for the code 301 to be on the screen during the POST routine is that your keyboard connector plug has worked its way out of the socket. Push it in and everything should be OK although it may be necessary to re-boot. Table 3: Video Adapator Follow your nose and try the switch settings, audio response etc. Video adapters can return 4xx, 5xx, 24xx and 39xx codes: 4xx Monochrome Display Adapter (MDA) errors 401 Monochrome memory test, horizontal sync frequency test, or video test failure 408 User indicated display attributes failure 416 User indicated character set failure 424 User indicated 80 x 25 mode failure 432 Parallel port test failure; monochrome display adapter 5xx Colour Graphics Adapter (CGA) errors 501 CGA memory test, horizontal sync frequency test, or video test failure 508 User indicated display attributes failure 51 6 User indicated character set failure 524 User indicated 80 x 25 mode failure 532 User indicated 40 x 25 mode failure 540 Oser indicated 320 x 200 graphics mode failure 548 User indicated 640 x 200 graphics mode failure 24xx Enhanced Graphics Adapter (EGA) errors 39xx Professional graphics controller errors 94 SILICON CHIP 1701 1702 1703 1704 1780 1 7 81 1 7 82 1 790 1791 Fixed Fixed Fixed Fixed Fixed Fixed Fixed Fixed Fixed disk disk disk disk disk disk disk disk disk POST error adapter error drive error adapter or drive error O failure 1 failure controller error O error 1 error Table 5: Floppy Disc Drives If the drive receives power separately from the computer (ie, it is an external drive), check that it is plugged into the power outlet and is turned on. Check the drive is configured correctly and for correct rotational speed. Check the voltages at the, power connector. Pin 4 should be at +5V (±0.2V) with respect to pin 2 while pin 1 sould be at + 1 2V (±0.6V) with respect to pin 3. 6xx Floppy drive/adapter errors 601 Floppy drive/adapter Power On Self Test Failure 602 Drive test failure; disk boot record is not valid 606 Disk change line function failure; drive error 607 Disk is write protected; drive error 608 Bad command; drive error 61 O Disk initialisation failure; track O bad 611 Time-out; drive error 61 2 Bad Controller chip 613 Bad Direct Memory Access; drive error 614 Bad Direct Memory Access; boundary overrun 61 5 Bad index timing; drive error 61 6 Drive speed error 621 Bad seek; drive error 622 Bad Cyclic Redundancy Check; drive error 623 Record not found; drive error 624 Bad address mark; drive error 625 Bad Controller chip; seek error 626 Disk data c6mpare error 73xx 3.5" external diskette drive errors 7306 Disk change line function failure; drive error 7307 Disk is write protected; drive error 7308 Bad command; drive error 731 O Disk initialisation failure; track O bad 7 311 Time-out; drive error 7 31 2 Bad Controller chip 7313 Bad Direct Memory Access; .drive error 7314 Bad Direct Memory Access; boundary overrun 7315 Bad index timing; drive error 7 31 6 Drive speed error 7 321 Bad seek; drive error 7322 Bad Cyclic Redundancy Check; drive error 7323 Record not found; drive error 7324 Bad address mark; drive error 7325 Bad Controller chip; seek error 7326 Disk data compare error Problems with your motherboard are not nice but it pays to check the obvious before calling in a technician. In particular, check that all external components (keyboard, monitor, disc drives, power supply & adapter cards) are plugged in and working correctly. kind of monitor and graphics board you are using. The same goes for the video adapter. If you think you may have a problem with the video board verify the switch settings on th~ motherboard and video card. Turn on the power and listen for the audio response produced by the POST (Power On Self Test). Most computer manufacturers use one beep to indicate success and two beeps for failure - although you should familiarise yourself with your own computer's POST characteristics. Try running the diagnostics to test the adapter. Note that adapters which are · not supported by the diagnostics will generally fail the tests even though they may in fact be good. But it wasn't working when I called you ... Intermittent problems are the most difficult to deal with and often there is only a report from a worried user who cannot describe the problem accurately. Interpreting a user's description then guessing why the problem occurred inevitably leads to frustration on all sides. Try getting the user to write down exactly what happened and, as far as possible, what was done in response. Try to re-create the problem yourself. Once you see the problem, try running appropriate diagnostic software. Most of the reputable manufacturers supply good to very good advanced diagnostics software with their computers. It is not there just because the programmer liked to test out the colour palette. Many diagnostics routines can be set to run many times over, thus continually testing the suspect equipment. Try alternately heating and cooling. Heat from a hair dryer can help find a problem, though do be very careful not to overdo it and cause damage to other components. Experience [sometimes bitter), practice and good old commonsense will tell you when enough is enough. Cooling can often have the opposite effect. Sometimes spraying the suspect component with a freezer spray will help isolate heatrelated failures . The time of day can also create problems due to the routine nature of machine operation, airconditioning temperature, humidity, and power requirements (both from within the building and from other buildings drawing power from the same line). Check the location of power and telephone cables in relation to your computer and so on. External influences can have a quite significant effect on your computer system. For those willing to proceed further with troubleshooting, rather than call in the cavalry [read: service technician), the following are some voltage measurements for various components, together with some [though by no means all) of the more common system messages gleaned from IBM technical and maintenance manuals. Naturally, you should consult your own manufacturer's manuals for information specific to your computer. Power supply The power supply voltage between pins 1 and 5 [ground) should be 4.5 to.. 5.4 volts DC on the system board connectors. If not within this range, the power supply is bad. Remember that if you want to test the power supply, it must be installed in the system and the system must be running. This is because it is a "switching" power supply and thus must always have a proper load to function correctly. If you take the power supply out of the system unit and plug it in, it will not operate. You need to have it plugged into the motherboard and attached to at least one disc drive. Keyboard troubles Keyboards typically return a 3xx error code. If you get one, turn off the computer, disconnect the keyboard and check the following voltages at the system board keyboard connector: Getting zapped Beware of static electricity and other external environmental influences. Static in particular can cause what appears to be an intermittent problem. Does the filing cabinet regularly "zap" you when you pass? Synthetic carpets can be a real problem in this regard. PIN 1 2 3 4 5 VOLTAGE +2 .0 to +5.5 +4.8 to +5 .5 +2 .0 to +5 .5 GROUND +2.0 to +5 .5 SEPTEMBER 1990 95