Anytime that I visit a client with a computer problem, I perform one VERY essential test. I would guess that the results from this test define upwards of 50% of the problems that a client is reporting.
Surprisingly, I have found a key issue to come in the form of a defective power supply. Sadly, many power supply testing units fail to monitor the -5 V.D.C. output from the power supply. This particular voltage requirement, based upon my research, is used primarily as an input voltage to the motherboard, and not to any cable-attached peripheral. Of course, if the client has various cards, be they video, cable T.V., NIC, or even audio, it is very likely that the problem being reported can be traced directly to a defective power supply.
I has been my finding, and therefor conclusion, that many problems that present themselves as a failure of a peripheral device (i.e.--CD or DVD drive, video, or even audio problems) are quickly cured by replacing a defective power supply. By no means do I want to convey the concept that a bad power supply is the sole cause of a problem. Frequently, the reason that a power supply has failed is the result of some peripheral that could be causing the the death of the power supply.
For those of us who have been in the business of computer hardware/software repair for many years, as in at least ten and preferably 20 years... we know that many computers that were highly marketed and sold to the general public contained grossly undersized power supplies. Without naming names, if you have had the experience I previously referred to, it was not uncommon to find power supplies that put out a mere 65 to 85 watts. I have observed also that certain brands of computers have grossly under-rated (as in inappropriate) power supplies in relation to the number of peripherals installed on a computer. In many cases, the issue is that the computer owner has added an additional peripheral (such as a DVD-RW drive) which, based on power supply failure, would indicate that the capabilities of said power supply were, at least some of the time, exceeded the capacity of a given power supply--resulting in that power supply dying, but only partially, on the spot. The secret seems to lie in testing that -5 V.D.C. connection.
For any technician worth her or his salt, testing a power supply should be THE VERY FIRST THING on their checklist when actually having a hands-on experience with said client's computer. I must admit that over my many years in this business, I used to get at least one call each week where the client was adamant about the fact their computer had failed, and needed repair. Of course, my first question was: "Oh, do you see that light on your computer screen?" "No???" Well, perhaps you should first hitting the "ON" button on your monitor. "O.K. Now has that fixed your problem?"
Look first for the obvious. Don't presume that some brand-new piece of malware has raped a client's computer. Hopefully, you will have, during the course of your initial conversation with said client, made sure that what some might consider as obvious facts to be taken into consideration.
Example: Me: "Oh, I noticed that you are calling me from your cell phone..."
Client: "Yes, I couldn't get through to you on the office phone."
Me: "How's the weather there?"
Client: "Oh, it is a perfectly sunny day."
Me: "Do me a favor, try turning on the lights in your office."
Client: "Um, nothing happens!"
Me: "Check with your neighbors and call me back. Ask them if their lights are working."
Customer (after a ten minute time-frame while we weren't connected) "Oh, yes, it appears that we have suffered from a power black-out in our office complex."
Me: "While, if you need to, please call me back about your computer problem after the power outage is resolved..."
It is, therefore, my opinion that MANY of the common problems that face us as computer guru's can be resolved by the application of a little common sense.
Common sense? I think that it should rule the waves, especially in our profession!!!
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