Voltage Testing – Every Repair Technician and Engineer Should Master This Skill
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By solely understanding the best way to be taught digital schematic diagram and testing digital components weren’t enough to make us an excellent digital repairers. Many faults can’t be detected even if you know how to exactly check out and check all the digital components because of these faults solely will likely be detected by merely performing a voltage check out. Are you conscious that pretty a numbers of Monitor points I’ve to hold out a voltage check out to have the ability to discover the defective components? Certain, if with out voltage testing, I would end up can’t uncover the fault and the Monitor have to be return once more to purchasers. What must you return many Screens once more to the similar purchasers? In reality your small enterprise fame might be affected and worst in case your opponents (completely different digital repairers) be able to restore it. You’d undoubtedly lose out the consumers and could also be very troublesome to get once more his perception as soon as extra about your performance to revive Screens.
I do know plenty of digital repairers significantly newbie’s would not have the braveness to hold out the voltage check out significantly Laptop Screens and Television because of they’d been afraid of the extreme voltage and get electrocuted. Successfully, in the event you want to work on this line and choose to not discover out about voltage testing (as a result of afraid), then you definitely’re truly missing one factor that will present assist to to revive any instruments fast. In any case, voltage testing is not that as dangerous as you thought to be. With some steering from restore buddies and even you check out it by your self (smart) and security from isolation transformer, I don’t see each different causes you don’t want to do the voltage testing. Furthermore this in spite of everything it’s a must to know the safety pointers first on this digital servicing self-discipline.
The precise tough question now’s though you know how to hold out the voltage testing; this does not guarantee that you will undoubtedly being able to treatment the digital points! As to why it’s possible you’ll’t treatment the problems will depend upon many parts much like:
– How successfully you are in understanding the capabilities of digital circuit (assuming I’m talking on the Monitor circuit). Some Screens circuits will likely be very refined to understand it.
– How good you are in tracing the digital circuit (assuming you are tracing from the availability to the faulty components) because of many digital repairers will misplaced observe and will’t go extra to detect the fault.
– How educated you are in understanding each function of the digital half. As an example, if no signal flowing to the underside of a transistor, in spite of everything there might be no current flowing between the collector and the emitter. One different occasion, what do you rely on the output voltage will doubtless be if 100 volts is passing through between a ten ohm resistor and a ten okay ohms resistor?
– Usually to have the ability to treatment a difficulty we by chance create far more points as a consequence of that we would not have the potential to hold tight the meter’s probes inflicting it to the contact on completely different pins whereas measuring a components (says is an IC or a transistor). This is ready to set off your entire instruments to shutdown and even burnt the components. What variety of of you should have completed that sooner than?
– We must always moreover know what the fluctuate of the meter setting is to have the ability to check out the digital circuit exactly. As an example, would you check out the secondary output voltages when your meter is about to AC fluctuate? Or would you rely on a finding out when your meter’s purple probe touches on a cold ground?
From above, these are the problems that you should know in the event you want to be effectively able to hold out a voltage check out on any instruments. It isn’t that simple to absorb all of the issues that I’ve merely talked about above nonetheless in case you’ve the eagerness to do it (I suggest research all of the issues from finding out electronics books, visiting dialogue board, doing all your particular person smart check out and and so forth) then you definitely’re giving your self a chance to check one factor that may truly revenue to you.
On this week’s article I am going to current you methods by performing a voltage check out has helped me to unravel an unusual draw back in a Laptop Monitor.
Successfully, this monitor with the mannequin establish of MIMOS (that’s an OEM Monitor) obtained right here in with the criticism of can’t modify horizontal dimension (there’s fully no modifications when the horizontal dimension administration was pressed). The present width (dimension) was large and all sides of the present curved inward (pincushion out). In your information, the horizontal dimension and pincushion circuit had been located within the similar area and every circuits had been working collectively to have the ability to get hold of a necessity present. If one half in a circuit fails, it’d affect one different circuit as successfully! That’s the reason, when the horizontal dimension circuit have draw back, the pincushion circuitry was affected too (the present curved inward).
Often as soon as I see this sort of draw back, I would usually check and try all the components throughout the horizontal dimension and pincushion circuits’ area with my ESR, analog and digital meter. Most of the time, I could treatment the problem fast. The widespread faulty parts for horizontal dimension width draw back in a Monitor had been usually dry joints, shorted modulation diode and pincushion transistor and capacitor opens alongside the horizontal dimension coil’s line. Nonetheless someway I could not discover the faulty components on this Monitor because of your entire components that I’ve checked had been all examined okay!
Since I’ve checked all the components throughout the horizontal dimension and pincushion circuit area to be okay, now the one method to treatment it is through using voltage check out. Often, every time in the event you want to perform voltage testing, one ought to start from the availability first. Nonetheless in case you might be experience enough it’s possible you’ll on a regular basis skip some half and start tracing the circuit that you just simply suppose would fail. As there are many digital restore newbie’s on this ERG member website, I would current all of you the best way to trace from the availability first.
Now assume twice, what makes the present to show into small or large every time the horizontal dimension administration was pressed through the On Show Present (OSD)? There ought to be an indication sends out from someplace to the horizontal dimension circuit to have the ability to administration the present. Am I correct? The pincushion transistor has a base pin and if this voltage varies (as a result of horizontal dimension administration each set to minimal or most) the present will change too. You probably can choose to trace backward begins from the underside pin of the pincushion transistor or start from the availability. I am going to info you to trace from the availability because of as quickly as you know how to trace from the availability, you will be able to troubleshoot and restore completely different Monitor points too much like can’t administration the brightness, distinction, vertical and horizontal peak. You would possibly use this technique that I’m about to level out you in TV and completely different digital instruments as successfully.
First it’s a must to understand what is the function of digital to analog conversion (DAC) circuit. Since plenty of the trendy Screens are using digital signal (communication between the CPU and EEPROM and completely different circuits as successfully) there ought to be some circuit to remodel the digital signal to analog signal to have the ability to drive the pincushion transistor and others digital circuits too. Our common multimeter can’t measure digital signal, it could nicely solely be taught analog signal. Older Screens have the DAC IC located out website the CPU (such as a result of the TDA8444 IC utilized in NEC XV 14 Monitor) whereas for modern Screens the DAC IC is constructed into the CPU. I suppose you in the intervening time are understood why a digital circuit desires a DAC as part of it full circuit. In several phrases, the DAC is required to talk with the analog world!
On this faulty Monitor, I don’t see any DAC IC shut by the CPU so I assumed that the DAC was already constructed into the CPU. Now, that’s basically essentially the most tough half the place it’s essential to fastidiously modify the Monitor place and your self so that when the Monitor vitality is change “ON” it’s possible you’ll perform the voltage check out on all the pins on the CPU. Assuming you should have taken all of the obligatory safety and precautions now’s the time to vary on the Monitor and start to do voltage testing.
After to procure preserve of the Monitor, select the horizontal dimension administration through the OSD show display. You might even see when the “+” and “-” buttons was pressed on the doorway panel, the amount throughout the OSD present signifies the minimal and most price representing the size of the present being adjusted. Since it’s a faulty Monitor, although the amount throughout the OSD show display is altering (since you might be pressing the “+” and “-“) there is no such thing as a such factor as a affect on the present and the present stays large and curved. Nonetheless someway you possibly can measure the pins on the CPU to search out which considered one of many pins the voltage is altering when the adjustment button is press! Try one after the other of many CPU pins until you seen one which has affect when the horizontal dimension administration was pressed. The voltage is about 0 to 5 volts (will depend upon the design of Screens) and can go up or down momentarily when the horizontal dimension adjustment is altering. Congratulation! You in the intervening time are have determined the availability of the horizontal dimension circuit. One phrase of advice, a defective CPU or a corrupted EEPROM info might set off no signal on the horizontal dimension provide pin!
After you’ve acknowledged the pin then it is comparatively simple to hunt out out the fault. Start tracing from the pin and see on the place the voltage had missing as confirmed on this image. Surprisingly the voltage stays okay even till pin 5 (inverting enter) of the quad operational amplifier LM324 IC. Since that’s an OP-AMP IC, it requires two inputs (inverting and non-inverting enter) to provide an output at pin 7 nonetheless the voltage at pin 7 would not vary. And if this output won’t vary undoubtedly it could nicely’t administration the horizontal dimension. Pin 5 voltage of the LM324 IC varies and pin 7 don’t varies then doubtless the problem is each throughout the IC itself or components which is likely to be related to pin 6 (non-inverting enter). I seen a wire coming from excessive of the board and upon inspecting it; it was from B+ voltage (about 66 VDC) and passing through a resistor sooner than reaching pin 6 of the OP-AMP IC. Using my analog meter to measure all through the extreme ohms resistor (820k), I found it to be zero voltage. To have the ability to truly affirm is the resistor fault, I desoldered considered one of many lead and check with my ohmmeter. Guess what? The resistor has open circuit! Unbelievable and it was true! Altering with a model new resistor restored the present once more to common.
Conclusion- Take into consideration if I didn’t use the voltage testing methodology, I have no idea the best way prolonged that I am going to spend on troubleshooting this sort of draw back. And worst nonetheless, I may end up can’t treatment the problem and return the Monitor once more to my purchaser. With fastened finding out and observe in digital restore you should not have any draw back in tackling any digital faults eventually. Merely don’t hand over and proceed to check from the ERG member’s net web page. Thank You for being my member.
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Source by Jestine Yong
