Voltage Testing – Every Repair Technician and Engineer Should Master This Skill
By only realizing how to read through electronic schematic diagram and tests electronic elements were not enough to make us a great digital repairers. Many faults are unable to be detected even if you know how to properly check and check all the digital components for the reason that individuals faults only can be detected by basically carrying out a voltage test. Do you know that fairly a numbers of Observe complications I have to carry out a voltage take a look at in order to find the defective elements? Yes, if with out voltage screening, I could end up cannot discover the fault and the Observe have to be return again to clients. What if you return quite a few Displays back to the same shoppers? Of program your business enterprise track record would be impacted and worst if your competitors (other electronic repairers) be capable to restore it. You would unquestionably lose out the shoppers and is extremely challenging to get again his rely on yet again about your ability to maintenance Displays.
I do know lots of electronic repairers primarily newbie’s do not have the bravery to conduct the voltage check specifically Computer Displays and Tv mainly because they ended up frightened of the high voltage and get electrocuted. Properly, if you want to do the job in this line and decide on not to understand about voltage testing (simply because of scared), then you are certainly missing a little something that can enable you to mend any tools rapid. Immediately after all, voltage testing is not that as perilous as you considered to be. With some steerage from maintenance close friends or even you take a look at it on your individual (simple) and safety from isolation transformer, I do not see any other causes you do not want to do the voltage testing. Besides this of study course you should know the protection suggestions initial in this digital servicing field.
The authentic hard concern now is even however you know how to accomplish the voltage tests this does not assure that you will unquestionably getting able to clear up the digital issues! As to why you cannot solve the complications is dependent on quite a few factors these types of as:
– How properly you are in comprehending the features of digital circuit (assuming I’m talking on the Keep track of circuit). Some Screens circuits can be quite difficult to recognize it.
– How superior you are in tracing the digital circuit (assuming you are tracing from the source to the defective factors) mainly because several digital repairers will missing keep track of and won’t be able to go more to detect the fault.
– How professional you are in understanding every single function of the digital ingredient. For illustration, if no signal flowing to the base of a transistor, of training course there would be no recent flowing concerning the collector and the emitter. Yet another instance, what do you count on the output voltage will be if 100 volts is passing as a result of between a 10 ohm resistor and a 10 k ohms resistor?
– In some cases in get to fix a difficulty we accidentally make even additional issues thanks to that we do not have the ability to keep tight the meter’s probes leading to it to contact on other pins whilst measuring a factors (states is an IC or a transistor). This would bring about the complete equipment to shutdown or even burnt the components. How several of you have performed that just before?
– We ought to also know what the range of the meter placing is in buy to exam the electronic circuit accurately. For example, would you exam the secondary output voltages when your meter is set to AC vary? Or would you be expecting a looking through when your meter’s red probe touches on a cold ground?
From above, these are the things that you should know if you want to be properly capable to complete a voltage examination on any products. It is not that effortless to take in almost everything that I’ve just pointed out above but if you have the enthusiasm to do it (I imply study every thing from reading through electronics publications, going to discussion board, accomplishing your have sensible take a look at and etc) then you are supplying you a probability to study a little something that will truly reward to you.
In this week’s write-up I’m going to clearly show you how by undertaking a voltage take a look at has helped me to remedy an unconventional issue in a Laptop or computer Keep track of.
Effectively, this observe with the brand name title of MIMOS (this is an OEM Observe) arrived in with the criticism of are not able to regulate horizontal dimension (you can find entirely no modifications when the horizontal measurement manage was pressed). The screen width (dimensions) was massive and both of those sides of the screen curved inward (pincushion out). For your information, the horizontal measurement and pincushion circuit were being situated in the similar region and equally circuits were doing the job jointly in get to achieve a want display screen. If a single ingredient in a circuit fails, it would have an affect on yet another circuit as very well! Which is why, when the horizontal dimension circuit have challenge, the pincushion circuitry was afflicted far too (the exhibit curved inward).
Usually when I see this kind of problem, I would generally check out and examination all the elements in the horizontal size and pincushion circuits’ region with my ESR, analog and digital meter. Most of the time, I could address the problem rapidly. The common defective areas for horizontal dimensions width difficulty in a Check have been commonly dry joints, shorted modulation diode and pincushion transistor and capacitor opens along the horizontal size coil’s line. But by some means I could not locate the defective parts in this Keep track of simply because all of the parts that I have checked had been all analyzed ok!
Given that I have checked all the elements in the horizontal dimensions and pincushion circuit place to be all right, now the only way to remedy it is by using voltage examination. Commonly, when if you want to execute voltage testing, just one should start out from the resource 1st. Having said that if you are knowledge sufficient you can usually skip some part and begin tracing the circuit that you think would fail. As there are many electronic restore newbie’s in this ERG member web site, I would display all of you how to trace from the resource initial.
Now believe diligently, what would make the display screen to become tiny or big any time the horizontal measurement management was pressed by way of the On Monitor Display (OSD)? There need to be a signal sends out from somewhere to the horizontal dimension circuit in order to regulate the screen. Am I proper? The pincushion transistor has a foundation pin and if this voltage varies (due to the fact of the horizontal measurement handle both established to least or utmost) the display will adjust as well. You can select to trace backward starts off from the base pin of the pincushion transistor or start from the supply. I will tutorial you to trace from the source mainly because as soon as you know how to trace from the resource, you would be in a position to troubleshoot and fix other Keep track of challenges far too these kinds of as cannot management the brightness, distinction, vertical and horizontal height. You might use this process that I am about to display you in Tv and other digital equipment as properly.
Very first you will have to fully grasp what is the function of digital to analog conversion (DAC) circuit. Because most of the contemporary Screens are utilizing electronic signal (interaction concerning the CPU and EEPROM and other circuits as very well) there need to be some circuit to transform the electronic signal to analog sign in get to push the pincushion transistor and some others digital circuits as well. Our typical multimeter cannot measure electronic sign, it can only browse analog sign. More mature Displays have the DAC IC located out web-site the CPU (such as the TDA8444 IC applied in NEC XV 14 Keep track of) whilst for fashionable Monitors the DAC IC is developed into the CPU. I guess you are now recognized why a electronic circuit wants a DAC as aspect of it complete circuit. In other words and phrases, the DAC is necessary to connect with the analog planet!
In this faulty Monitor, I really don’t see any DAC IC close by the CPU so I presumed that the DAC was presently crafted into the CPU. Now, this is the most tough section the place you have to very carefully regulate the Keep track of placement and you so that when the Keep track of electric power is change “ON” you can accomplish the voltage examination on all the pins at the CPU. Assuming you have taken all the essential protection and precautions now is the time to switch on the Monitor and start to do voltage testing.
Soon after you acquired keep of the Watch, find the horizontal size manage through the OSD display. You could see when the “+” and “-” buttons was pressed at the entrance panel, the amount in the OSD display screen signifies the least and highest benefit symbolizing the sizing of the show remaining modified. Considering the fact that this is a faulty Check, while the amount in the OSD display is changing (since you are urgent the “+” and “-“) there is no influence on the exhibit and the screen stays massive and curved. But somehow you could measure the pins at the CPU to locate which a person of the pins the voltage is shifting when the adjustment button is press! Try just one by one particular of the CPU pins right until you saw one that has outcome when the horizontal sizing regulate was pressed. The voltage is about to 5 volts (depends on the style and design of Displays) and must go up or down momentarily when the horizontal measurement adjustment is shifting. Congratulation! You are now have decided the source of the horizontal size circuit. A single word of information, a defective CPU or a corrupted EEPROM data could lead to no sign at the horizontal sizing source pin!
The moment you have regarded the pin then it is reasonably uncomplicated to discover out the fault. Start out tracing from the pin and see at wherever the voltage had lacking as proven in this picture. Remarkably the voltage remains ok even until pin 5 (inverting input) of the quad operational amplifier LM324 IC. Considering that this is an OP-AMP IC, it demands two inputs (inverting and non-inverting enter) to produce an output at pin 7 but the voltage at pin 7 would not fluctuate. And if this output will never vary surely it can not handle the horizontal measurement. Pin 5 voltage of the LM324 IC differs and pin 7 do not varies then most most likely the problem is possibly in the IC itself or elements that are similar to pin 6 (non-inverting enter). I saw a wire coming from major of the board and upon inspecting it it was from B+ voltage (about 66 VDC) and passing by way of a resistor ahead of achieving pin 6 of the OP-AMP IC. Employing my analog meter to evaluate across the substantial ohms resistor (820k), I discovered it to be zero voltage. In purchase to definitely affirm is the resistor fault, I desoldered a single of the direct and test with my ohmmeter. Guess what? The resistor has open up circuit! Unbelievable and it was accurate! Changing with a new resistor restored the exhibit again to ordinary.
Conclusion- Imagine if I did not use the voltage screening approach, I don’t know how extensive that I’m likely to invest on troubleshooting this kind of difficulty. And worst nevertheless, I might conclusion up are unable to remedy the challenge and return the Keep track of back again to my consumer. With frequent discovering and apply in electronic repair you will have no difficulty in tackling any electronic faults in the long run. Just will not give up and continue to master from the ERG member’s webpage. Thank You for becoming my member.
