Voltage Testing – Each and every Maintenance Technician and Engineer Really should Master This Skill

By only understanding how to read through electronic schematic diagram and testing digital factors have been not more than enough to make us a good electronic repairers. Quite a few faults can not be detected even if you know how to properly test and verify all the electronic factors due to the fact people faults only can be detected by basically undertaking a voltage test. Do you know that rather a quantities of Keep an eye on issues I have to execute a voltage test in buy to locate the faulty factors? Certainly, if without voltage testing, I could finish up won’t be able to uncover the fault and the Check have to be return back to buyers. What if you return several Screens back again to the exact prospects? Of course your organization name would be impacted and worst if your rivals (other electronic repairers) be able to restore it. You would surely lose out the shoppers and is really tricky to get again his trust again about your ability to fix Screens.

I do know a lot of digital repairers specially newbie’s do not have the courage to conduct the voltage take a look at specially Personal computer Displays and Tv because they were fearful of the large voltage and get electrocuted. Very well, if you want to operate in this line and select not to find out about voltage screening (for the reason that of worried), then you are really missing a little something that can enable you to fix any machines quick. After all, voltage screening is not that as unsafe as you thought to be. With some guidance from mend close friends or even you test it on your very own (useful) and safety from isolation transformer, I will not see any other explanations you never want to do the voltage testing. Besides this of study course you need to know the basic safety recommendations 1st in this digital servicing field.

The serious tough query now is even nevertheless you know how to execute the voltage tests this does not assurance that you will unquestionably remaining able to address the digital problems! As to why you are unable to solve the problems depends on several variables these kinds of as:

– How effectively you are in knowing the functions of digital circuit (assuming I’m conversing on the Watch circuit). Some Monitors circuits can be very intricate to realize it.

– How very good you are in tracing the electronic circuit (assuming you are tracing from the supply to the faulty components) because quite a few digital repairers will missing observe and can’t go more to detect the fault.

– How well-informed you are in knowing each and every purpose of the digital component. For example, if no sign flowing to the base of a transistor, of program there would be no latest flowing among the collector and the emitter. A different case in point, what do you count on the output voltage will be if 100 volts is passing by means of involving a 10 ohm resistor and a 10 k ohms resistor?

– Occasionally in purchase to resolve a dilemma we unintentionally build even extra issues because of to that we do not have the capability to maintain restricted the meter’s probes leading to it to touch on other pins though measuring a parts (states is an IC or a transistor). This would bring about the entire products to shutdown or even burnt the factors. How several of you have completed that just before?

– We ought to also know what the vary of the meter location is in get to examination the electronic circuit precisely. For instance, would you check the secondary output voltages when your meter is set to AC assortment? Or would you count on a examining when your meter’s purple probe touches on a chilly floor?

From higher than, these are the factors that you ought to know if you want to be successfully able to perform a voltage examination on any tools. It is not that effortless to take up all the things that I’ve just outlined previously mentioned but if you have the passion to do it (I signify learn almost everything from reading through electronics publications, visiting discussion board, accomplishing your own simple test and etc) then you are giving by yourself a chance to master a little something that will actually gain to you.

In this week’s article I am going to display you how by doing a voltage check has assisted me to remedy an unusual dilemma in a Laptop Keep an eye on.

Effectively, this keep track of with the brand title of MIMOS (this is an OEM Keep track of) came in with the criticism of can’t modify horizontal sizing (you will find completely no modifications when the horizontal dimensions control was pressed). The exhibit width (size) was large and each sides of the display screen curved inward (pincushion out). For your information and facts, the horizontal dimensions and pincushion circuit were located in the identical space and both equally circuits have been performing collectively in buy to reach a drive exhibit. If just one part in a circuit fails, it would have an impact on a further circuit as nicely! That’s why, when the horizontal dimensions circuit have challenge, the pincushion circuitry was afflicted too (the screen curved inward).

Generally when I see this form of problem, I would generally look at and check all the elements in the horizontal measurement and pincushion circuits’ region with my ESR, analog and digital meter. Most of the time, I could remedy the challenge rapid. The typical faulty components for horizontal size width challenge in a Watch had been commonly dry joints, shorted modulation diode and pincushion transistor and capacitor opens alongside the horizontal dimension coil’s line. But by some means I could not find the defective factors in this Observe because all of the elements that I have checked were being all analyzed alright!

Since I have checked all the components in the horizontal size and pincushion circuit space to be okay, now the only way to clear up it is by applying voltage test. Frequently, anytime if you want to accomplish voltage testing, a person should commence from the supply first. However if you are working experience more than enough you can generally skip some portion and start out tracing the circuit that you imagine would fail. As there are many electronic repair service newbie’s in this ERG member website, I would demonstrate all of you how to trace from the resource initial.

Now assume meticulously, what helps make the display screen to turn out to be modest or big every time the horizontal dimensions manage was pressed through the On Display Exhibit (OSD)? There must be a signal sends out from somewhere to the horizontal dimensions circuit in get to command the display. Am I ideal? The pincushion transistor has a foundation pin and if this voltage differs (because of the horizontal dimensions control possibly set to minimum amount or utmost) the display will modify way too. You can decide on to trace backward starts from the foundation pin of the pincushion transistor or start out from the supply. I will information you to trace from the resource mainly because when you know how to trace from the resource, you would be equipped to troubleshoot and mend other Keep an eye on difficulties far too such as can’t management the brightness, distinction, vertical and horizontal top. You may use this system that I am about to exhibit you in Television and other digital equipment as effectively.

1st you should recognize what is the perform of digital to analog conversion (DAC) circuit. Since most of the fashionable Monitors are using electronic sign (conversation in between the CPU and EEPROM and other circuits as nicely) there need to be some circuit to change the electronic sign to analog sign in get to drive the pincushion transistor and other individuals digital circuits too. Our typical multimeter are unable to evaluate electronic signal, it can only examine analog signal. Older Monitors have the DAC IC located out web page the CPU (these kinds of as the TDA8444 IC applied in NEC XV 14 Check) whilst for modern-day Monitors the DAC IC is constructed into the CPU. I guess you are now understood why a electronic circuit desires a DAC as section of it comprehensive circuit. In other words, the DAC is needed to connect with the analog environment!

In this defective Keep track of, I will not see any DAC IC close by the CPU so I presumed that the DAC was now built into the CPU. Now, this is the most tough component where you have to carefully alter the Watch situation and by yourself so that when the Keep an eye on power is swap “ON” you can complete the voltage test on all the pins at the CPU. Assuming you have taken all the essential security and precautions now is the time to swap on the Watch and get started to do voltage tests.

Just after you received maintain of the Check, pick the horizontal size control by the OSD monitor. You could see when the “+” and “-” buttons was pressed at the front panel, the quantity in the OSD show signifies the least and most value representing the sizing of the display remaining adjusted. Given that this is a faulty Check, although the variety in the OSD display screen is altering (since you are urgent the “+” and “-“) there is no effect on the show and the screen continues to be massive and curved. But somehow you could evaluate the pins at the CPU to track down which just one of the pins the voltage is transforming when the adjustment button is press! Test a single by 1 of the CPU pins right up until you noticed a single that has impact when the horizontal sizing handle was pressed. The voltage is about to 5 volts (is dependent on the style and design of Screens) and need to go up or down momentarily when the horizontal dimensions adjustment is shifting. Congratulation! You are now have established the resource of the horizontal sizing circuit. Just one word of guidance, a defective CPU or a corrupted EEPROM data could trigger no sign at the horizontal dimension resource pin!

After you have known the pin then it is fairly straightforward to obtain out the fault. Commence tracing from the pin and see at wherever the voltage had lacking as proven in this image. Shockingly the voltage remains ok even until pin 5 (inverting input) of the quad operational amplifier LM324 IC. Considering the fact that this is an OP-AMP IC, it necessitates two inputs (inverting and non-inverting input) to develop an output at pin 7 but the voltage at pin 7 would not range. And if this output is not going to change surely it can not management the horizontal measurement. Pin 5 voltage of the LM324 IC may differ and pin 7 really don’t varies then most likely the issue is either in the IC alone or factors that are related to pin 6 (non-inverting enter). I noticed a wire coming from prime of the board and upon inspecting it it was from B+ voltage (about 66 VDC) and passing by way of a resistor in advance of reaching pin 6 of the OP-AMP IC. Working with my analog meter to measure across the significant ohms resistor (820k), I discovered it to be zero voltage. In purchase to seriously validate is the resistor fault, I desoldered one of the lead and check with my ohmmeter. Guess what? The resistor has open circuit! Unbelievable and it was genuine! Changing with a new resistor restored the exhibit back to regular.

Conclusion- Think about if I failed to use the voltage screening strategy, I do not know how prolonged that I am heading to expend on troubleshooting this sort of difficulty. And worst nevertheless, I may possibly stop up can’t fix the difficulty and return the Observe again to my consumer. With regular discovering and exercise in electronic restore you will have no problem in tackling any electronic faults in the upcoming. Just do not give up and continue on to study from the ERG member’s web page. Thank You for getting my member.