Troubleshooting a problem with a computer is somewhat of an science because there are so many possible causes for some problems and it is necessary to eliminate them one by one. Trouleshooting a problem with a computer is also somewhat of an art in that you can dramatically speed the resolution process when you know what the most likely causes of a particular problem are and test for those first.

Deciding exactly where to start depends on just what the problem is that you are trying to troubleshoot. I can't therefore tell you precisely what to do to correct your particular problem. Instead I am going to use an actual problem that I recently had to resolve and go through the steps that I took to resolve the problem and hopefully that will give you some ideas on how to tackle your own computer problems.

There are three different types of computer problem that you might face.

Don't worry if you don't quite understand the difference between these three, the example I am about to present actually had three separate problems, one of each type, so as I describe the process I went through in resolving the problem you will see examples of each type of problem and how you might try to resolve it.

The particular problem that I am going to discuss is one where a computer connected to a printer via a serial cable refused to print. Now this is a rather unusual combination and I don't expect any of you to be confronted by this precise problem but the steps that I followed should still be of interest.

What has changed?

That is the first question that you should ask when confronted with something that used to work but doesn't any longer. (If it has never worked then you probably don't have it set up right in the first place).

In my case what had changed was that the motherboard had recently been replaced which in effect meant that I had an entirely new hardware configuration that had never worked to print to this printer.

Check for trivial errors first

Before I replaced the motherboard the computer had been set up with a serial cable from the COM2 port to the printer. The obvious place to start therefore is to check that the cable is plugged in properly (it was) and that it runs from the correct port on the computer to the correct port on the printer.

I discovered that I had plugged the cable into the wrong port on the computer. It was plugged into COM1 instead of COM2.

Two possible fixes presented themselves. I could either transfer the cable to the correct port (COM2) or reconfigure the computer to expect the cable on COM1.

The first of these is the easier solution so I tried that first and shifted the cable. Unfortunately this didn't fix the problem (there was still no response from the printer) so I tried the second solution and reconfigured the printer driver to change to COM1. Printing a test page from the properties dialog worked but unfortunately this didn't really fix the problem - the printer reported "ERROR 22" which is a configuration error when I tried printing from a program.

Check Software Configuration

The intriguing question now was not only why the computer wouldn't print but also why the different responses from the COM1 and COM2 ports. What was different between the way that they were set up?

The most obvious possibilities were that either the COM2 port was disabled in the BIOS or that the internal cable connecting the COM2 port to the motherboard was plugged in backwards.

The first of these could be checked without having to dismantle the computer so I rebooted the computer, pressed DEL at the appropriate time so as to get into the BIOS and then hunted through the various settings looking for the COM2 configuration. When I finally found the option it appeared to be set up correctly so that wasn't the solution.

Okay, since COM2 was configured correctly in the BIOS, the problem appears more likely to be hardware so let's leave it for the moment and see if we can get the printer working on COM1.

It had been several years since I had previously configured a serial connection to this printer so it took me a while to remember that there are a number of different protocols that can be used for serial communication and that these need to be configured the same on both the computer and the priinter.

I went into the printer properties and located the advanced settings for the serial communication setup. I made a note of these settings and then worked out the appropriate combination of buttons on the printer (a HP Laserjet 4) to bring up the same information there.

The cause of the configuration problem became obvious. The computer was set to use hardware communication control while the printer was expecting software communication control. Changing the printer to use hardware control (XON/XOFF) fixed the problem and the computer could now print successfully to COM1.

Check the Hardware

COM2 still refused to work. Since I preferred to put the connection to the printer on COM2 (since it saves an adaptor cable) I thought it would be a good idea to get COM2 working properly as well. This would be particularly useful if at some future time I want to attach another serial device to the computer.

To check the hardware you must first power down the computer and then unplug the power cable from the back of the computer.

I next opened the case and looked at the cable running from the motherboard to the COM2 port on the back of the computer. The connector at the computer end was actually keyed in this instance so that it couldn't be inserted the wrong way around so that couldn't be the problem.

In troubleshooting hardware problems it is always useful to have spare hardware that can be swapped for the hardware that you think may have a problem since if using a different piece of hardware gives the same problem then you can be fairly sure that the problem lies elsewhere.

I hunted through my collection of computer spares and managed to locate another cable. I unplugged the original cable from the motherboard and plugged in the spare in its place. I then reassebled the computer and turned it on. Once it had booted up I tried again to print to the printer on COM2.

The printer now functioned properly.


A methodical approach to solving this problem by testing out the more trivial, simpler, and more likely solutions first indicated that there were in fact not one or two but three separate problems stopping the computer from being able to print.

Firstly the printer cable was plugged into the wrong port on the back of the computer (a trivial mistake and easily rectified). Secondly the communications protocols used by the computer and printer did not match (a software configuration error). Thirdly, the cable used to connect the COM2 output from the motherboard th the back of the case (which came out of my spares box since one was not supplied with the new motherboard) had in fact failed in some way (a hardware failure).

I recommend that you approach troubleshooting any problems that you have with your computer using ths step by step approach.

Whatever has most recently changed is most likely related to the problem and so will help you to identify the most likely causes of the problem. Testing for the simplest, trivial causes first will get things fixed fastest if that turns out to be the problem while not adding significantly to the time taken to solve the problem if it does not. Software errors are easier to check for and much more likely to occur than hardware errors and so where the problem could be either, check the software first.

Almost all of the problems that you have with your computer will have a single cause, this one was very unusual in that I had to fix three separate problems before I could get things working properly (but then changing a motherboard is a rather drastic change to the configuration and so having multiple problems is more likely than when you make other smaller changes to your system).

I hope that the above gives you some ideas on how best to approach resolving the problems that you have with your computer system.


This article written by Stephen Chapman, Felgall Pty Ltd.

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