Question 5) CompTIA’s A+ Core Hardware Exam

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SubObjective: Recognize common problems associated with each module and their symptoms, and identify steps to isolate and troubleshoot the problems. Given a problem situation, interpret the symptoms and infer the most likely cause.
Single Answer Multiple Choice

 

You are having trouble establishing a connection to the Internet. You suspect the external 56-Kbps modem connected to your Windows 98 workstation is failing. What is the best way to determine whether the modem’s transmission and receiving hardware is working properly?

 

A. Attach a loopback connector to the serial port.
B. Use TRACERT to determine where the connection is failing.
C. Test the modem by performing analog and digital loopback tests.
D. Use a multimeter to determine whether any signals are being transmitted or received.

 

Answer:
C. Test the modem by performing analog and digital loopback tests.

 

Tutorial:
Modems transmit and receive data through a serial port. The most thorough way to test any serial port is to perform a loopback test.

 

To test the modem hardware itself, you need to perform analog and digital loopback tests on the modem.

 

In a modem analog loopback, keyboard data is sent to the modem where it is modulated into analog format, sent in a loop back to the receiver portion of the modem, demodulated into digital format, and returned for verification to the monitor screen.

 

In a modem digital loopback, the computer sends digital data to the modem, and the modem immediately returns the data to the monitor screen to verify functionality. The serial port and cable are also verified in the process.

 

The loopback test is a very effective way to ensure that a suspect serial or parallel port is functioning properly. However, this test will not insure that the modem is functioning properly.

 

There are two types of serial port loopback tests: internal and external. The internal loopback diagnostic makes sure the digital signals are being produced correctly. You should unplug any cables from the port before running this type of diagnostic. The external loopback diagnostic tests whether the port is transmitting and receiving analog signals correctly. It is generally more effective than the internal.

 

The external diagnostic requires you to connect a wrap plug to the port you want to test. The wrap plug is a device that connects the port’s send pins to its receive pins. When the test is run, the wrap plug routes the send data back to the port’s receive pins so that the port is transmitting and receiving data at the same time. If you plug a loopback connector into the end of the cable, the diagnostic can test both the port and the data cable.

 

Tracert is used to determine the route taken by data packets from one computer to another.

 

A multimeter is used to measure voltage and might provide useful information in this case, but this would not be the best way to test the modem.

 

Reference:
1. A+ Training Guide – Symptoms and Troubleshooting
– Troubleshooting Modems

 

These questions are derived from the Self Test Software Practice Test for CompTIA Exam #220-301: A+ 2003 Core Hardware.

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