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By Conrad Persson; Persson is editor of ES&T. Many electronics servicing professionals still see computers as arcane machines operated by highly trained specialists and as inaccessible to ordinary mortals. At one time, that may have been true, but it is not true any longer. In fact, as this special report will demonstrate, many of today's small computers have entered the realm of "consumer electronics products" and are candidates for repair by consumer electronics servicing facilities. The situation today can be compared to the situation with the automobile as it evolved from the early days to today. In those early days, the automobile was owned by a few well-to-do people, who employed chauffeurs to drive them and who may have found it hard to find a mechanic to keep the cars in operation. The operation of those machines was beyond the average individual. Only a few skilled mechanics and a few brave do-it-yourselfers were servicing them. Not long ago, computers were in the same category. The promise was great, but if you bought one, who would pro gram it, who would fix it? They were pretty expensive, and the software, if it was available, was even more expensive. Besides, with dozens of manufacturers, there was no standardization. That situation has changed. In the business computer field, IBM and the clones it has inspired have become a de facto standard. IBM is also the choice of many owners of home personal computers. Apple and the MacIntosh more or less have become the computer of choice in schools and are also a popular choice in homes, especially with people who are involved with graphics. There are a few others, notably the Commodore, Amiga and Atari, but when a servicing technician is called in to service a computer, he will most likely be facing an IBM, clone or Apple product. The prices of computers have come down dramatically over the past few years. Although it may still require considerable thought on the part of many consumers before they buy one, prices are now low enough that most middle income families can afford to buy a powerful personal computer. And they are buying them. In fact, as I was in the process of writing this introduction, my copy of U.S. News and World Report arrived. This week's issue contains an 11-page special report on "The Wired Household:' The information presented in the issue indicates that there are computers in many U.S. homes: 22% of all households in this country have computers. A lot of good software programs for both office and home are available off the-shelf, and more is being added every day. One of the most popular types of software is the word processor. This type of program is useful for basic functions, such as letter writing and preparing school papers. Then there are the financial programs. Some of these can help you keep track of your checkbook, print checks, keep track of whether expenses are taxable, simplify preparing your federal income tax return, and keep track of your stock portfolio. There are simple database programs that allow the user to keep track of mailing lists, record albums, books, home inventory. There are communications programs that allow you to bank at home, order your own airline tickets, buy and sell stocks, and look up almost anything any time of night or day from one of the on-line databases. This list does not even begin to scratch the surface. There are scores of off-the-shelf educational, recreational, desktop publishing programs and much more. In short, the computer has become a tool that is accessible to anyone with between $1,000 and $3,000 to spare. With the increasing availability of useful, low cost programs, the computer has joined the ranks of the TV, the microwave and the boom box as consumer products. One thing separates the computer from many of the other consumer products: It is expensive enough to be thought of as a serviceable product, not just a throwaway. Something else to keep in mind is that many of these computers are in the hands of people who have not figured out how to set the clocks on their VCRs or program them to record a program at a later date. Besides the servicing opportunities provided by the potential for electronic or mechanical failure in these units are the servicing opportunities presented by relatively unsophisticated people operating a sophisticated product, and needing help to do so. That being the case, if you have not at least looked into the possibility of servicing this class of products, you might be missing a good bet. The tools of the trade With computers, as with any other of today's consumer electronics products, a servicing technician can dip his toe in to test the water or plunge in with both feet. It all depends on the way an individual goes about things. You can go out and buy all of the sophisticated test equipment needed to troubleshoot and start out repairing down to the component level, or you can start out using little more than the tools and test equipment you already have and gradually add new items as you need them. You can go into it with the determination to solve every knotty problem yourself, or you can fix the ones that are easily with in your capability and refer the tough ones to the depots while you increase your computer-servicing knowledge. There are two relatively inexpensive pieces of computer-servicing equipment you might want to acquire to go on the bench or in the toolbox along with the DMM and scope: the breakout box and the logic probe. If you have ever taken a look at the connector that goes be tween the computer and the printer, you will see that there are a lot of wires. Al though it looks complex, anyone who can handle a TV wiring harness should have no problem here. The only problem is that computers often are not like TVs. In a given TV, unless the manufacturer messed up, the wires in a harness should go from point to point exactly as it shows on the schematic. With a computer connecting cable, the individual wires may not terminate properly, depending on the kind of printer used. If a cable has wires that connect to the wrong points at one or both ends, obviously your computer and printer will not communicate properly. The printer may fail to print at all, or it many output some strange stuff. The problem is determining which wires end up where. That's where the breakout box comes in. In operation, the breakout box is connected to both sides of the interface. For example, if the problem is with a printer interface, one side would be connected to the computer and the other side to the printer. Connected in this manner, all communications lines would flow through the breakout box. LEDs on the box then show whether positive or negative logic signal voltage is present on each pin on each side of the box. Switches and jumpers allow the servicing technician to reroute misrouted connections to restore the system to proper operation. The logic probe. The logic probe is a simple, inexpensive device that can help track down problems in a computer that is malfunctioning. In its simplest form, it consists of a self-contained probe that contains logic circuitry and LED indicators and can indicate whether a logic signal is present at a given point in the circuit. A sophisticated probe will have indicators to show whether the test point i high or low or is exhibiting pulses. Some will even have a memory or pulse stretcher, which will show the presence of a single-shot pulse of such a short du ration that it lights the indicator too briefly to be recorded by the human eye or doesn't light it at all. To use the logic probe, you would troubleshoot the computer problem down to a circuit board, then probe suspect components. Using repair depots If you are contemplating going into computer servicing, there is plenty of help out there -- for a price. If you take in a computer for servicing and find that you are in over your head, you can ship the unit, a circuit board or a disk drive to a depot, which will complete the repair. If you are thinking about starting in computer servicing, contact one or several servicing depots to determine their terms, conditions and reliability. If you are on the verge of making a decision to service computers, establish some kind of agreement beforehand so you will know how you'll handle depot servicing requirements. Table 1 is a list of computer repair depots that you might contact. If you do send anything to a depot that will be returned rather than exchanged, always make sure to note the positions of any switches or jumpers, such as DIP switches, before you send the unit off. The depot may have to change their positions to complete the repair, and there is no guarantee they will be reset to the original positions. This could cause a lot of head-scratching if the unit does not operate properly when it is returned. The rest of the report The other articles in this report are designed to bring you important information on the current computer and computer-repair situation. The article "Servicing Zenith Microcomputers, Part VI" is a continuation of the Zenith personal-computer series by John Ross. This part contains some tips on under standing and troubleshooting the memory section of this popular computer. The article "Tele-servicing: A Team Approach to Field Service" introduces a new computer/software/oscilloscope combination that essentially makes the probes of an oscilloscope as long as the telephone lines. Table 1--Servicing depots CAM America Computer Parts 562 Lincoln Blvd. Middlesex, NJ 08846 201-560-8584 Datatech Depot 2524 E. Fender Ave. Fullerton, CA 92631 714-680-0383 Distributed Technologies 19823 58th Place S. Kent, WA 98032 206-395-7800 DMA 611 Development Blvd Amery, WI 54001 715-268-8106 Impact Printhead Services 8701 Cross Park, Suite 101 Austin, TX 78754 512-832-9151 PTS PO. Box 272 Bloomington, IN 47402 800-333-PTS-1 Repair Pro/D.S. Walker 11210 Steeplecrest, Suite 300 Houston, TX 77065 713-890-2257 Victor Computer Services 8125 Westglen Drive Houston, TX 77063 713-789-1888 Also see: Tele-servicing: A team approach to field service |
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