Using Comparison Method to Solve Electronic Repair Problems

Many times I solved lots of electronic repair problems by using the comparison method. So what is comparison method? Comparison method means that you compare two identical equipment circuits in terms of measuring resistance; signal and voltage test and see if there is any different in result. If you get different result meaning the circuit or components under test is at fault. Thus, with the right information you had gathered, the chances for you to repair the equipment is very high.

If a repair technician or engineer use this comparison method, it is usually means that they are facing difficulty in finding the original part number of certain electronic components (may be due to from a burnt circuit), no schematic diagram available, do not understand how a new circuit works, missing components (taken out by some irresponsible electronic repairers), want to solve electronic problem fast and etc.

I personally do not always use this method unless I had confirmed that all the electronic components in a certain circuit or area were tested good and still not be able to find the faulty parts. Let’s put this as an example, a Monitor came in with blue colour missing. This problem normally lies in the CRT blue colour circuit. It could be a bended blue signal pin at VGA connector, a broken signal wire in the VGA cable, dry joints in the blue circuit, defective components in blue circuit, faulty CRT socket or even a bad PC Tube. And also we assumed that the EEprom IC data is in good order (for your information, a corrupted EEprom data can cause missing colour too).

If I have tested all the components that are related to blue circuit and still could not find the fault, I have no choice other than to use the comparison method. Comparison method not only has helped me to locate the fault, it also speed up and save my troubleshooting time. Some faults were really beyond your understanding as an electronic repairer such as intermittent tiny hairline cracked in the circuit; inexperienced tech installed a transistor in the other way round, tiny solder bridge across components legs and etc.

With the caused I have just mentioned above, if without using the comparison method, you may get frustrated and many troubleshooting hours are lost and at the end of the day the equipment still can’t be repaired or worst if the customer want it back urgently. The pressure is on you and I hope with this article at least it will lighten up your burden. There are four types of comparison methods you can use to repair the electronic problems.

The first method is to use Ohmmeter (preferably analogue meter as I found it more accurate than the digital meter) to compare the resistance between the two identical circuit. Power have to be off and if the circuit you want to compare have some big capacitors, I guess you have to discharge it before you do any comparison as the extra voltage in the filter capacitor can cause a misleading information (different result with the board you are comparing) and you thought that you have found the faulty section. Set your analogue meter to X 1 Ohm and start comparing between point to point of each electronic component. Certain electronic circuit will only have response when you set your meter scale to higher range such as X 10 or even X 100. If the results you get have some differences then put your attention upon the circuit or component you are checking. Who knows you might have found the solution.

Second method is to compare voltage using a digital meter. I do not encourage using analogue meter as I found it not really precise as certain circuit even have a volt different the circuit may not functioning well. Be extra careful when doing the voltage comparison test as the power is “On”. Any slip from the test probe and touch on other components may cause a heavy spark (if you are comparing the supply line) or even the equipment will totally shut itself down. If you are not careful, you may end up create more problems than you can solve. Concentration and know what you are measuring (comparing) is the key of success in voltage testing.

Third, you can use an oscilloscope to compare the signal between the electronic equipment. You will be surprise that I found lots of electronic problems solution by comparing the signals. This method is exactly the same with the voltage comparison method except that you are now looking at signal and not on digital meter. Be extra careful too when comparing the board with oscilloscope as the equipment has to be “On”. Get some books on how to use oscilloscope as in the long run it really benefits you.

The fourth method is to use Analog Signature Analysis to compare the boards without power “ON”. I’m using Huntron tracker 2000 to do the job. This test equipment applies a current-limited AC sine wave across two points of an electronic component or circuit under test. The resulting current/voltage waveform is shown on a signature display using vertical deflection for current and horizontal deflection for voltage. This unique Tracker signature represents the overall health of the part being analyzed. By comparing the signatures of known good circuit boards to those of suspect boards, faulty nets and components can be quickly identified. You can get or bid for a used Huntron Tracker at Ebay dot com if you have lots of similar electronic boards for repair.

What if I could not locate or do not have the same equipment or model for comparison? If you have read my previous post I always mentioned about the emphasis on friendship among electronic repairer. You just can’t be a lone electronic repairer; you HAVE to mix around if you want to be successful in this repair line. I will call my electronic repair friends to check out if they have any same model of equipment and if they have, I will ask them to “lend” one for me and will return it back as soon as possible. Assuming I do not have or can’t get from my repair friends, I will tell my customers to hold on for few more days hope there will be a similar equipment send for repair. Many times after waiting just for couples of days, yes the same equipment came for repair sent by other customers.

If everything I have tried and still no way to solve the problem, I will just let the customer know. Usually they will accept my explanation and some of it would send to the supplier for repair of course with a higher charge.

Conclusion- In electronic repair one must have the flexibility on how to solve a problem. There are no certain ways to solve it as electronic problems are quite dynamic. You have to use the best method to encounter different problems in electronic. If possible invest in the test equipment that can really speed up your troubleshooting job.