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Posts Tagged ‘Monitor’

Repair Your Own LCD Monitor

30 Jul

Nowadays nearly every PC owners are using LCD monitor or replace their old CRT Monitor to a better LCD monitor. LCD monitor has an advantages over the old CRT monitor. Sitting in front of CRT monitor for a long hours can cause eyes strain. But using LCD monitor you don’t have to worry about this kind of problem but LCD monitor also consume less electricity. Besides that LCD monitor only cost a little bit above the price of CRT monitor.

Some LCD monitor will have a problem after a few years of usage but for your information LCD has a life span more than 10 years. If your LCD monitor have a problem you have a three options, (1) send it to computer repair shop so that it can be repair, (2) buy a new LCD monitors to replace it, and (3) repair the monitor yourself. If you choose option number one you probably have to pay around half the of the monitor price but it depends on the problem itself. But it will cost a lot if you opt for option number two and its not recommended unless you have enough budget. And the last option, you will ask yourself “How can I repair LCD monitor?”. Yes, it is possible to repair your own LCD monitors with the guide of Jestine Yong’s ebook call “LCD Monitor Repair”.

LCD Monitor Repair ebook is a complete guide step by step on how to repair your own LCD monitors. Its cover the most of the common problem like power with no display, white display, shut down after hardly a second and dim display. The knowledge of repairing LCD monitor is an essential technical skills and everyone should learn because not only you can save money by repairing you LCD monitors problem but also can make a few bucks by helping your friends fixing their problematic LCD monitors.

Your friends will amaze how you learn to repair LCD monitors. And thank to the LCD Monitor Repair for guiding you to become an LCD Monitor expert.

LCD Monitor Repair is an absolute guide to become an expert in repairing and fixing LCD monitors problem. Visit LCD Monitor Repair to get more information about the guide and start your journey to become LCD monitor specialist.

 
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Dell Monitor Repair (Likom L705xxx Model) With No Power Symptom

15 Mar

This DELL 17” Monitor (Made in Malaysia under LIKOM model L705XXX, product no: L7055LP) came in with no power symptom. Normally after opening up the cover I would look at the power supply (primary side) for any burnt and cracked components first. If there are darkened area and burnt components, I would tell myself that this Monitor needs a little more time to repair it. If it is not (component’s intact) I would usually begin to discharge the filter capacitor and start checking the fuse.

Okay, it is confirmed that all the primary side components looks good in this Monitor.

First, discharge the big fat filter capacitor with a resistor (I know that the voltage already drained off but it is a normal procedure for me because what if the start up resistor has an open circuit?) then check the fuse.

If the fuse is okay, experience will tell you that the bridge diodes are also working fine. Place your black probe of your analog meter set to x1 to the center pin (drain) of the power FET and red probe to the other pin one at a time (gate and source). If the pointer of the meter doesn’t kick then 80 % of the Power FET is okay. If you want to 100% confirm if it is good then you have to solder it out and test. If the pointer shows a reading then most probably the power FET has developed a short circuit. The result that I got from this Monitor was the pointer don’t flick.

Now is the time for me to use the dick smith flyback tester to check the smps primary winding. The result that I got was, the led bar don’t lit. Ah ha! That was a clue and this clue tells you that it is either the smps primary winding is shorted or one of the secondary diodes has given way. Of course you can check all the secondary diodes with your normal multimeter first (remember, every electronic repairers have their own procedure methods of troubleshooting) but I prefer this way as I want to confirm also if the smps primary winding is working or not.

Usually smps transformer is very robust thus I didn’t suspect it to pull down the flyback tester reading. I straight away check all the secondary diodes with my analog meter and found one diode shorted (part number U202G). Since I do not have this part number, I use a UF5404 ultra fast recovery diode as a replacement. In fact I use this UF5404 to all 14 to 17” Monitor as a replacement for all part number of secondary diodes. The spec of this diode was 400volt, 3 Amp with 50 nanosecond.

After the replacement of the diode, and placing the flyback tester probes again to the primary winding, the result shows full bar on the LED. Don’t be happy with the result yet because your job still hasn’t done.

Now I moved on to check HOT with the same procedure as checking the power FET. The HOT checked to be okay too. Next, I check the internal capacitance of the flyback transformer to see it is shorted or not or is the capacitance value run. For your information, internal capacitor in flyback transformer gave lots of problems in computer Monitor. I also scanned thru the B+ FET and found it to be good too.

Now is the time to switch on the Monitor, however this round I don’t connect any bulb because it was only a shorted diode in the secondary side. I would only connect a light bulb after repair when there is major short circuit in the primary side such as a blown bridge rectifier, shorted fet and smps primary winding and also burnt components in the board.

The DELL 17” Monitor worked beautifully and after long hours of burn-in test, I declared it okay and ready to send back to my loyal customer. Isn’t it fun to be able to repair a Monitor and at the end you get paid for something you like doing. I just love electronic repair!

Check out the two links below. You will be pleasantly surprised to find out that LCD and Electronic Repairs are so Easy and Highly Profitable for even a novice. You can learn the repairing secrets easily.

Find out How to Repair Any LCD Monitor – It is a breeze!

Learn the Secrets of Testing Electronic Components.

 
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Understanding The High Voltage Transistor In Computer Monitor

28 Jan

High voltage transistors are transistors with higher specification than the normal transistor. It is usually located in the area of power transformer such as the switch mode power transformer and flyback transformer. In television and monitor that uses the flyback transformer to generate high voltage, a high voltage transistor is required to perform the job. It’s location mainly beside the flyback transformer and attach to a heat sink in order to transfer heat faster. Otherwise it may blow in a very short time due to the hard work of this transistor in switching. Typical part number of high voltage transistor that used in monitor and TV is BU2508DF, C3998, C5148, C5047, C5589, C5803 and etc. Usually their rating of volt, amp and watt is in the 1500 volt and above, 10 amps, 50 watt and more. Their sizes are much bigger than the common signal transistor. If this high voltage transistor is shorted, you have to find the exact replacement part number in order for the equipment to last longer. Substitution part number usually won’t last long-perhaps in the few weeks or few months time and it will blow again unless you know the storage and the fall time of the transistor.

Higher voltage, ampere and wattage will not guarantee that your transistor will last long. Many times a bigger specification will blow in a split of seconds the moment you switch on the equipment. You have to go to that particular manufacturer to get the transistor datasheet and find out the spec of the transistor. Look for the fall time and storage time value. The original and the replacement value should have tolerance of not more than 20%. If not the replacement transistor will run hot and eventually blow the transistor. This will waste your precious time.As to why sometimes even the nearest specification transistor also won’t work well is because the particular equipment such as monitor-the yoke coil and the flyback transformer is designed based on the specification of the transistor.

Thus, only original part number transistor that can be install in that particular equipment. I have seen even the original number with different batch of transistor when install in the monitor causing the display to curve in (pincushion out) and the transistor runs very hot. I’ve checked all the circuit and components that connected to the transistor to be okay. Even replacing the flyback transformer also won’t help. The transistor’s temperature keeps rising and if I don’t turn off the monitor, I believe it will eventually blow the transistor. I took out the transistor and compared with the original one and discovered that the replacement logo is a little bit different from the original transistor logo. When I called my electronic supplier about the logo, they said that the transistor that I bought is of a newer version, thought from the same factory. After long hour of searching for the original transistor, I managed to find one. Unbelievable, the original transistor that i replaced runs cool and the picture is perfectly fine. Guess what is the high voltage transistor part number? It was C5148!

In another case, there was one Monitor came in with no power symptom. Upon carefully check the high voltage area; I confirmed that only HOT shorted causing no power. After the replacement (the part number was BU2508DF), when the monitor is switch on, the power blink. I thought that there was some other bad components are causing the power to blink. I check again the power and high voltage section but just could not locate the fault. I took out the HOT that I had just replaced and realize that it was a little bit different from the original one. I took out another HOT that is exactly the same from my spare parts compartment and voila the monitor works perfectly okay. I begin to compare both HOT and you can clearly see the different from the picture shown below.

The lesson that I learned from this mistake is always must replace with an original part number (if possible) and don’t buy any components that is cheaper than the normal market price.

Check out the two links below. You will be pleasantly surprised to find out that LCD and Electronic Repairs are so Easy and Highly Profitable for even a novice. You can learn the repairing secrets easily.

Find out How to Repair Any LCD Monitor – It is a breeze!

Learn the Secrets of Testing Electronic Components.

 
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How To Restore A 17″ Monitor CRT Picture Tube

20 Jan

The first part of the article mentioned about how you can tap from the secondary diode to get the desire output through the 7808 voltage regulator. The weakness of this circuit is that it can’t power up the 17” Monitor because the power supply have some limitation in delivering current to the bigger CRT tube. The power supply will either shut itself off or power blink. In order to counter this problem, we have to tap voltage from some other places in the Monitor. Unfortunately there were no more places (point) in the Monitor where you can tap the voltage to power up the bigger CRT tube. Due to we could not locate the point then we have to create (design) our own circuit. The best is to use the Monitor flyback transformer ferrite core and with wire loop around the core will produce high pulse ac. This high pulse ac can’t be measure by your normal meter.

With few turning at the core (external loop), you can get a higher ac output voltage to power up the CRT heater. This method only applies if you want to brighten up a Television picture tube. You can’t use this way on Monitor CRT because as mentioned earlier in the first part of the article, Monitor runs on different resolution. The higher the resolution, the higher the B+ voltage supply to the primary winding of the flyback transformer. The higher the B+ voltage, the greater is the voltage output at the secondary side making the output voltage (ac) produced by the external loop even higher. Thus this will make a sudden increase in the filament voltage causing an instant bright in the Monitor raster. Some monitor designed will shutdown if it detect a sudden brightness in the raster.

Even if the monitor didn’t shutdown and if the user decide to lower the Monitor resolution, the raster will suddenly become too dim due to lower B+ voltage. You may ask yourself why computer Monitor has its own 6.3 vdc output and why not like TV, the heater voltage comes from the secondary winding of TV flyback transformer? The answer is because the Monitor designer wants a steady 6.3 volt for filament and don’t want the raster to be affected by a changing in Monitor resolution. In order to solve this problem, after making about 7 to 10 loops around the flyback transformer core, you have to convert this high pulse ac into DC voltage. You can’t simply use any diodes for this purpose. A general purpose diode like the famous 1N5401-1N5408 would not be able to work in this circuit. The high pulse ac voltage will immediately kill the diode once the Monitor is switched “on”. You have to use an ultra fast recovery diode to do the job.

For your information, not all ultra fast recovery diode can efficiently run on this circuit. You have to select the diode type that has a faster speed time like a 50 nanosecond and below. I had tried a 75 nanosecond ultra fast recovery diode and it blown at 800 by 600 resolutions but work well in the 640 by 480 resolution. After done some R & D, I found that the best part number to use is the UF5404. This diode has the specification of 400V, 3A and 50ns. Once you have connected the ac voltage to the diode, you now have to use a filter capacitor to filter off the ripple. You can use a value of 220 to 1000 microfarad 50V. Measure the output DC voltage and make sure it must have about at least 15 to 20 over volts before you solder to pin 1 of 7808 voltage regulatorYou can also try to use a 7809 if the display is not bright enough. Don’t use any voltage regulator that is higher than 7809 otherwise the heater filament will get too hot and burn.

Pin 3 of the voltage regulator is the output and it must joint to the heater pin at the CRT board as shown in the photo. Carefully place all the wires in a strategic location and attach the voltage regulator at the heat sink beside the flyback transformer. You are now ready to switch on the Monitor and check if there is improvement in the display. If it okay then burn in test the Monitor for couples of days to check if the display is still bright and clear. If you are not satisfied with the sharpness, you can try to increase another volt by changing the voltage regulator part number to 7809. Some technicians prefer to use a variable voltage regulator such as the LM317T with a variable resistor so that they can adjust to the desire voltage. If the picture tube is still dim and no way that you can improve the display, I guess the time is up for the CRT tube. You either replace a used tube or return the Monitor back to the customer. I hope you enjoy reading this article. If so, please feel free to share this article with your friends or simply forward this article to anyone you wish! There’s no limit on the number of people you can share this with! If you have a question or comment about anything in this article, drop me an email. Your feedback is welcome!

Check out the two links below. You will be pleasantly surprised to find out that LCD and Electronic Repairs are so Easy and Highly Profitable for even a novice. You can learn the repairing secrets easily.

Find out How to Repair Any LCD Monitor – It is a breeze!

Learn the Secrets of Testing Electronic Components.

 
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