22/05/2024

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Voltage Tests – Every single Mend Technician and Engineer Must Grasp This Skill

Voltage Tests – Every single Mend Technician and Engineer Must Grasp This Skill

By only being aware of how to go through electronic schematic diagram and testing electronic factors were not plenty of to make us a good electronic repairers. A lot of faults cannot be detected even if you know how to precisely exam and test all the electronic factors simply because all those faults only can be detected by basically accomplishing a voltage check. Do you know that very a numbers of Monitor complications I have to conduct a voltage test in buy to identify the defective factors? Indeed, if without voltage tests, I may well stop up can’t discover the fault and the Watch have to be return again to shoppers. What if you return several Screens back to the similar customers? Of class your business enterprise popularity would be affected and worst if your competition (other digital repairers) be equipped to repair it. You would absolutely drop out the clients and is very complicated to get back again his have confidence in once more about your ability to mend Displays.

I do know plenty of digital repairers in particular newbie’s do not have the courage to conduct the voltage examination specifically Laptop or computer Monitors and Tv since they were being scared of the high voltage and get electrocuted. Very well, if you want to operate in this line and pick not to find out about voltage testing (for the reason that of fearful), then you are definitely missing a thing that can assistance you to repair service any gear speedy. Following all, voltage testing is not that as risky as you thought to be. With some steerage from repair pals or even you take a look at it on your personal (useful) and defense from isolation transformer, I will not see any other reasons you don’t want to do the voltage tests. Aside from this of program you should know the security tips to start with in this digital servicing industry.

The genuine complicated dilemma now is even while you know how to perform the voltage testing this does not warranty that you will certainly getting capable to solve the digital challenges! As to why you are not able to address the complications is dependent on numerous variables these types of as:

– How very well you are in knowing the capabilities of digital circuit (assuming I am chatting on the Check circuit). Some Monitors circuits can be incredibly complex to comprehend it.

– How excellent you are in tracing the digital circuit (assuming you are tracing from the source to the faulty elements) due to the fact many digital repairers will lost track and are unable to go even further to detect the fault.

– How well-informed you are in comprehension each function of the digital component. For case in point, if no signal flowing to the base of a transistor, of course there would be no present-day flowing among the collector and the emitter. A further instance, what do you anticipate the output voltage will be if 100 volts is passing via involving a 10 ohm resistor and a 10 k ohms resistor?

– Sometimes in order to fix a difficulty we unintentionally create even more difficulties owing to that we do not have the ability to maintain restricted the meter’s probes resulting in it to touch on other pins although measuring a parts (suggests is an IC or a transistor). This would trigger the complete machines to shutdown or even burnt the factors. How many of you have done that just before?

– We need to also know what the assortment of the meter setting is in get to examination the digital circuit precisely. For illustration, would you test the secondary output voltages when your meter is set to AC assortment? Or would you anticipate a looking at when your meter’s pink probe touches on a chilly ground?

From earlier mentioned, these are the things that you must know if you want to be properly able to execute a voltage examination on any tools. It is not that effortless to take in every thing that I’ve just talked about previously mentioned but if you have the passion to do it (I imply understand every thing from reading electronics textbooks, checking out discussion board, carrying out your individual practical check and and so on) then you are providing on your own a chance to learn a little something that will definitely advantage to you.

In this week’s report I am likely to show you how by accomplishing a voltage exam has helped me to address an unconventional problem in a Computer system Observe.

Well, this keep track of with the brand name name of MIMOS (this is an OEM Check) came in with the grievance of are not able to modify horizontal size (you can find completely no modifications when the horizontal measurement command was pressed). The show width (size) was significant and each sides of the display screen curved inward (pincushion out). For your facts, the horizontal sizing and pincushion circuit had been located in the exact same area and both circuits were doing work collectively in order to realize a wish display. If just one element in a circuit fails, it would have an impact on an additional circuit as properly! That is why, when the horizontal sizing circuit have problem, the pincushion circuitry was influenced far too (the display curved inward).

Typically when I see this variety of challenge, I would usually test and test all the parts in the horizontal measurement and pincushion circuits’ location with my ESR, analog and electronic meter. Most of the time, I could fix the problem fast. The widespread faulty pieces for horizontal dimension width dilemma in a Keep an eye on had been normally dry joints, shorted modulation diode and pincushion transistor and capacitor opens along the horizontal dimension coil’s line. But somehow I could not track down the defective parts in this Monitor since all of the elements that I’ve checked had been all examined okay!

Since I have checked all the components in the horizontal sizing and pincushion circuit place to be alright, now the only way to clear up it is by utilizing voltage take a look at. Usually, every time if you want to conduct voltage testing, 1 should start off from the source initial. However if you are encounter sufficient you can constantly skip some area and start tracing the circuit that you imagine would are unsuccessful. As there are quite a few electronic repair newbie’s in this ERG member web page, I would show all of you how to trace from the source initially.

Now think carefully, what helps make the show to develop into little or big each time the horizontal sizing command was pressed by means of the On Display screen Screen (OSD)? There need to be a signal sends out from someplace to the horizontal dimensions circuit in get to control the exhibit. Am I suitable? The pincushion transistor has a foundation pin and if this voltage may differ (for the reason that of the horizontal dimensions management either established to minimal or highest) the display will alter also. You can decide on to trace backward starts from the foundation pin of the pincushion transistor or start out from the resource. I will tutorial you to trace from the supply for the reason that the moment you know how to trace from the supply, you would be in a position to troubleshoot and mend other Check difficulties as well such as are unable to regulate the brightness, contrast, vertical and horizontal height. You might use this technique that I am about to show you in Television set and other digital tools as perfectly.

First you will have to realize what is the function of digital to analog conversion (DAC) circuit. Given that most of the modern Monitors are employing electronic sign (communication concerning the CPU and EEPROM and other circuits as perfectly) there will have to be some circuit to transform the digital signal to analog signal in buy to generate the pincushion transistor and other folks digital circuits as well. Our standard multimeter are not able to evaluate electronic signal, it can only examine analog signal. Older Screens have the DAC IC located out web page the CPU (these as the TDA8444 IC used in NEC XV 14 Check) though for contemporary Monitors the DAC IC is built into the CPU. I guess you are now comprehended why a digital circuit demands a DAC as section of it comprehensive circuit. In other terms, the DAC is needed to connect with the analog world!

In this defective Keep an eye on, I never see any DAC IC nearby the CPU so I presumed that the DAC was now built into the CPU. Now, this is the most hard aspect in which you have to cautiously alter the Watch situation and on your own so that when the Watch power is switch “ON” you can carry out the voltage check on all the pins at the CPU. Assuming you have taken all the needed security and safety measures now is the time to swap on the Keep an eye on and begin to do voltage screening.

Just after you received hold of the Observe, choose the horizontal measurement management by way of the OSD screen. You could see when the “+” and “-” buttons was pressed at the front panel, the selection in the OSD display signifies the least and optimum worth symbolizing the dimensions of the exhibit staying altered. Considering that this is a faulty Keep track of, whilst the number in the OSD monitor is shifting (simply because you are urgent the “+” and “-“) there is no outcome on the show and the exhibit stays big and curved. But someway you could evaluate the pins at the CPU to track down which a single of the pins the voltage is altering when the adjustment button is press! Attempt 1 by just one of the CPU pins until eventually you observed just one that has impact when the horizontal dimension regulate was pressed. The voltage is about to 5 volts (relies upon on the style and design of Displays) and must go up or down momentarily when the horizontal dimensions adjustment is switching. Congratulation! You are now have established the supply of the horizontal measurement circuit. Just one term of advice, a faulty CPU or a corrupted EEPROM information could cause no sign at the horizontal sizing supply pin!

After you have recognized the pin then it is rather easy to discover out the fault. Get started tracing from the pin and see at where by the voltage had lacking as proven in this photograph. Incredibly the voltage stays ok even till pin 5 (inverting enter) of the quad operational amplifier LM324 IC. Given that this is an OP-AMP IC, it necessitates two inputs (inverting and non-inverting input) to deliver an output at pin 7 but the voltage at pin 7 would not range. And if this output would not vary absolutely it can’t manage the horizontal sizing. Pin 5 voltage of the LM324 IC varies and pin 7 really don’t varies then most in all probability the challenge is either in the IC alone or parts that are similar to pin 6 (non-inverting input). I noticed a wire coming from top rated of the board and on inspecting it it was from B+ voltage (about 66 VDC) and passing through a resistor right before reaching pin 6 of the OP-AMP IC. Making use of my analog meter to evaluate across the large ohms resistor (820k), I discovered it to be zero voltage. In purchase to seriously ensure is the resistor fault, I desoldered 1 of the guide and check with my ohmmeter. Guess what? The resistor has open circuit! Unbelievable and it was true! Replacing with a new resistor restored the exhibit again to standard.

Summary- Consider if I failed to use the voltage screening method, I don’t know how very long that I am heading to shell out on troubleshooting this sort of problem. And worst nevertheless, I might stop up cannot resolve the trouble and return the Keep an eye on again to my buyer. With constant discovering and practice in electronic mend you will have no difficulty in tackling any digital faults in the long run. Just really don’t give up and carry on to master from the ERG member’s site. Thank You for being my member.