UPGRADING REPAIRING PCs

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174 Chapter 6—Serial Ports and Modems 1. Right-click the My Computer icon and select Properties. Or, you can open Control Panel and left-click the System icon twice. Then, click the Device Manager tab, Ports entry, and select a specific port (such as COM 1). 2. Click the Properties button and then click the Resources tab to display the current resource settings (IRQ, I/O) for that port. 3. Check the Conflicting Devices List to see whether the port is using resources that conflict with other devices. If the port is in conflict with other devices, click the Change Setting button and then select a configuration that does not cause resource conflicts. You might need to experiment with these settings until you find the right one. 4. If the resource settings cannot be changed, they most likely must be changed via the BIOS Setup. Shut down and restart the system, enter the BIOS setup, and change the port configurations there. In addition to the COM 1/COM 3 and COM 2/COM 4 IRQ conflicts noted earlier, some video adapters have an automatic address conflict with COM 4’s I/O port address (not IRQ). You can also use the Modems Diagnostic tab (discussed earlier in this chapter) to test a serial port, whether or not a modem is actually present. Advanced Diagnostics Using Loopback Testing One of the most useful types of diagnostic test is the loopback test, which can be used to ensure the correct function of the serial port and any attached cables. Loopback tests are basically internal (digital) or external (analog). You can run internal tests by unplugging any cables from the port and executing the test via a diagnostics program. The external loopback test is more effective. This test requires that a special loopback connector or wrap plug be attached to the port in question. When the test is run, the port is used to send data out to the loopback plug, which routes the data back into the port’s receive pins so that the port is transmitting and receiving at the same time. A loopback or wrap plug is nothing more than a cable that is doubled back on itself. Following is a list of the wiring necessary to construct your own loopback or wrap plugs. Check with the vendor of your testing software to determine which loopback plug design you need to use, or purchase pre-built ones from the vendor.
Loopback Plug Pinouts—Serial Ports • Standard IBM type 25-Pin Serial (Female DB25S) Loopback Connector (Wrap Plug). Connect the following pins: 1 to 7 2 to 3 4 to 5 to 8 6 to 11 to 20 to 22 15 to 17 to 23 18 to 25 • Norton Utilities (Symantec) 25-Pin Serial (Female DB25S) Loopback Connector (Wrap Plug). Connect the following pins: 2 to 3 4 to 5 6 to 8 to 20 to 22 • Standard IBM type 9-Pin Serial (Female DB9S) Loopback Connector (Wrap Plug). Connect the following pins: 1 to 7 to 8 2 to 3 4 to 6 to 9 • Norton Utilities (Symantec) 9-Pin Serial (Female DB9S) Loopback Connector (Wrap Plug). Connect the following pins: 2 to 3 7 to 8 1 to 4 to 6 to 9 Serial Port Configuration 175 To make these loopback plugs, you need a connector shell with the required pins installed. Then, you must wire wrap or solder wires, interconnecting the appropriate pins inside the connector shell as specified in the preceding list (see Figure 6.3). One advantage of using loopback connectors is that you can plug them into the ends of a cable that is included in the test. This can verify that both the cable and the port are working properly.
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UPGRADING AND REPAIRING PCs TECHNIC
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Associate Publisher Greg Wiegand Se
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Contents 1 General Technical Refere
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Contents vii IDE Hard Drive Identif
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Serial Port Configuration 172 Avoid
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Contents xi Sound Quality Standards
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About the Authors Scott Mueller is
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watch, photograph, and (occasionall
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Tell Us What You Think! As the read
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Chapter 1 General Technical Referen
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Understanding Bits, Nibbles, and By
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Note Glossary of Essential Terms 5
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Glossary of Essential Terms 7 Table
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Glossary of Essential Terms 9 Table
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Table 1.5 Hexadecimal/ASCII Convers
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Hexadecimal/ASCII Conversions 13 Ta
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Table 1.5 Hexadecimal/ASCII Convers
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Hexadecimal/ASCII Conversions 17 Ta
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20 Chapter 2—System Components an
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36 Caution Chapter 2—System Compo
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38 Table 2.15 Troubleshooting Power
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44 modules can be divided by 9, but
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50 Other Add-On Card Configuration
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Chapter 3 3 BIOS Configurations and
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Where BIOS Updates Come From 71 Tab
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How to Recover from a Failed BIOS U
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Note A complete list of PnP device
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Other BIOS Troubleshooting Tips 77
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Determining the Motherboard Manufac
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Determining the Motherboard Manufac
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Table 3.8 Common Keystrokes Used to
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Phoenix BIOS Beep Codes The followi
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Port 80h Beep Code Codes Error Mess
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BIOS Configuration Worksheet 89 BIO
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BIOS Configuration Worksheet 91 Sha
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4 SCSI and IDE Hard Drives and Opti
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Cable key prevents improperly plugg
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Breaking the 504MB (528-Million-Byt
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Table 4.3 Using LBA Mode Operating
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5. Use the #4 option—View Current
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Using LBA Mode 103 Table 4.6 Why ID
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Sources for BIOS Upgrades 105 Table
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Improving Hard Disk Speed 107 Figur
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Bus-Mastering Chipsets for IDE 109
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Table 4.13 Bus-Mastering Chipsets b
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Table 4.14 Other IDE Drive Installa
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standard single-ended SCSI devices
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SCSI Drive and Device Configuration
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SCSI Drive and Device Configuration
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Following these tips will help mini
Page 141 and 142: SCSI Configuration Troubleshooting
Page 143 and 144: Using FDISK 125 Using FDISK FDISK i
Page 145 and 146: Benefits of Hard Disk Partitioning
Page 147 and 148: How FDISK and the Operating System
Page 149 and 150: How FDISK and the Operating System
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Page 153 and 154: The command switches are explained
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Page 159: Troubleshooting Optical Drives 141
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Page 178 and 179: 160 Table 5.13 High-Performance Tap
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Page 186 and 187: 168 Table 6.2 25-Pin (PC, XT, and P
Page 188 and 189: 170 Table 6.4 Overview of UART Chip
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Page 208 and 209: 190 Chapter 7—Parallel Ports, Pri
Page 210 and 211: 192 Building a Parallel Loopback Pl
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