CompTIA®A+ Exam Notes : Troubleshoot common problems related to motherboards, RAM, CPU,And Others


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4. Hardware and Network Troubleshooting

4.1 Troubleshoot common problems related to motherboards, RAM, CPU and power with appropriate tools

1. On a personal computer, the general errors and the corresponding failures are shown below: 100-199 : System board failures 200-299 : Memory failures 300-399 : Key board failures 400-499 : Monochrome video problems 500-599 : Color video problems 600-699 : Floppy disk errors 1700-1799: Hard disk problems.

2. Some of the frequently encountered error codes and their corresponding error messages on a PC are given below.

Error Code Error Message
161 CMOS battery failure: Replace the CMOS battery
164 Memory size error : If the error occurs after memory upgrade, run SETUP program. 
201 Memory test failed : RAM chips failed, one or more may need to be replace. 
301 Keyboard error: You may have to check the key board 

3. A toner probe is an electronic test instrument to help trace wires. One part (the tone generator) induces a tone on a pair of wires, and with the other you part (the tone probe) you can detect the tone at the other end to trace where the wires go. You can trace wires through walls using a tone probe, and determine which pair is carrying the signal you induced at the other end.

toner probe

4. A cable tester is used to verify that all of the intended connections exist and that there are no unintended connections in the cable being tested. When an intended connection is missing it is said to be "open". When an unintended connection exists it is said to be a "short" (as in short circuit). If a connection "goes to the wrong place" it is said to be "miswired" (the connection has two faults: it is open to the correct contact and shorted to an incorrect contact).

cable tester

5. The main difference between a cable tester and a toner probe is that in the former, you have access to the both ends of the cable at the same time, and you normally to Open or Short testing (to determine right pins are connected), and in the latter, you dont have simultaneous physical access to both ends of the cable. An AT computer will have two interrupt controllers. The second interrupt controller needs to deliver the interrupts through the primary interrupt controller. IRQ2 had been identified for this purpose on the primary and IRQ9 on the secondary interrupt controllers. In other words, IRQ2 and IRQ9 are cascaded.

6. AT style systems use two power connectors, P8 and P9 to connect to the motherboard. ATX systems use only one P1 connector to connect to the motherboard.

7. If you are getting a keyboard error, you need to do one of the following things: a. Check if the keyboard needs to be cleaned b. Check if the keyboard cable has become loose c. Check if one or more of the keys are stuck d. If required, replace the keyboard.

8. The battery is supposed to provide backup in the event of any power failure, typically up to 2 hours or more.

9. The best ways to find whether a new hardware is supported by your Windows OS is to check the manufacturer's documentation first, and then the Hardware Compatibility List (HCL).

10. The inverter board is responsible for converting low voltage DC power to high voltage AC, necessary to light up the back-light bulb. If the inverter board is bad, the LCD screen (back-light bulb) will not light up when you turn on the laptop, but you still should be able to see a very dim image on the screen.

11. The most likely cause for excessive paging is insufficient Memory. Increase the physical Memory on your computer.

12. Date and Time Not Set is the most common error that occurs when the BIOS battery is drained. You need to replace the CMOS battery.

13. The most likely cause for sporadic movement of mouse is dirt. If dirt has entered the mouse, clean the dirt with IPA, or cotton wetted in soap water.

14. The most likely problem is conflicting IRQs. Since the mouse is working until the modem is used, the IRQ/IO address of modem may be conflicting with that of the mouse.

15. The motherboard displayed has the following expansion slots:

  • PCI slots : 5 (distinguished by white color, usually the number of PCI slots available on a motherboard varies from 3 to 6)
  • ISA slots: 2 (distinguished by black color, longer than PCI slots, placed next to PCI slots.)
  • AGP slot: 1 ( The single slot, next to 5 white PCI slots is AGP slot in brown color. Note that there will be only one AGP slot)

16. To obtain BIOS string ID: a. Power off the system b. Either unplug your keyboard or hold down one of the keys on the keyboard c. Power-on the system and you should get a keyboard error d. The string in the lower left hand corner of your computer screen represents the BIOS String ID.

17. It is also possible to read the BIOS information by going to the BIOS set-up of the PC by pressing appropriate key (usually Del key) during boot up.

18. Various POST (Power On Self Test) error codes and their description is as below:x is any single digit integer.

  • Code 01: Undetermined problem
  • Code 02: Power Supply error
  • Code 1xx: System board errors
  • Code 2xx: Memory (RAM) errors
  • Code 3xx: Keyboard errors
  • Code 6xx: Diskette Drive errors

19. The following are true about backup:

  • Full backup: Here all files that have been chosen for backup are backed up, irrespective of whether the archive bit is set or not set. Archive bit is set (ON) after backup.
  • Incremental backup: Here only the files that have been created or have changed since the previous full or incremental backup will be backed up. The archive bit is set after a file is backed up.
  • Incremental backup will backup files that have changed since previous full or incremental backup. d. Differential backup: Here, the files that have changed or created since the last full backup will be backed up. Note that, unlike Incremental backup, the archive bit is not set on a differential backup. The result of this is that the next differential backup will include files that were backed up during earlier Differential backups.

20. UPS usually contains a filter to smooth the noise, and this filter is called noise filter.

21. x86 (32-bit) operating systems have a memory limit of 4GB. If you intend to use greater than 4GB of memory, you need to upgrade to x64 bit operating system.

22. Startup Repair can prevent a time-consuming reinstallation by diagnosing and repairing problems that prevent Windows from starting. Startup Repair is designed to start automatically if Windows detects a startup problem. The Startup Repair tool in Windows 7 can help fix problems that prevent Windows from starting up.

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