BenQ T705 LCD Monitor Problem in C5707 Transistor - Repair Guide
This BenQ T705 LCD Monitor has a standard fault of display shutdown after few you "On" for few seconds. The cause of the problem was normally a shorted one or two of the C5707 push pull transistors. In addition to the shorted transistor, one additionally has to test the tuning capacitor for top ESR value with the help of ESR meter. If you do not personal one, you should utilize the digital capacitance meter to test the capacitance value. However, from my expertise, checking only the capacitance value does not guarantee that the capacitor is nice except you confirm it with ESR meter. The reason why I emphasis on checking this tuning capacitors was as a result of the capacitors have a excessive failure rate that might cause the C5707 transistor to go shorted. You even have to observe the high voltage transformer pins carefully. I had come throughout quite plenty of shorted C5707 transistors brought on by dry joints in pins of the excessive voltage transformer.
In this case, as traditional after I've confirmed that only two C5707 transistors shorted, I began to test the tuning capacitors and examine the pins of the high voltage transformer. Both the tuning capacitors found to be okay but there were dry joints within the transformer pins. Contemporary solder was utilized to the high voltage transformer pins and I'm able to "On" the LCD Monitor. Guess what? The Monitor has the identical symptom once more which is display shutdown after few seconds! I do not imagine it as most of the time it will certainly work as it is a common fault!
I started to recheck the encompassing parts which have connection to the C5707 transistors but found no faults in it. Analyzing the board many times did not reveal any improper soldering job. There have to be something that has gone flawed that had caused the LCD Monitor to shutdown. Deep in my coronary heart I don't suspect backlights drawback as a result of the C5707 transistors shorted was brought on by dry joints within the high voltage transformer. Beside, the backlights were fairly reliable for this BenQ LCD Monitor model.
Considering again, I purchased a brand new badge of C5707 transistors from my digital suppliers not long ago. The center pin (leg) is a bit shorter than the opposite two as proven from the photo below. I thought to myself would it be this badge of transistors which have drawback causing the display shutdown after few seconds? In fact I am unable to blindly suspect the transistors except I've some proof of it. The discovering begins..................
Testing the C5707 transistor with an analogue meter set to X 1 and to X 10 Ok Ohm would not seem to be it has problem. Evaluating the outcome with an original C5707 transistor did have some distinction in the X 10 K Ohm vary but the studying is acceptable from my years of experience in testing transistor. The only thing that I have never in contrast is the Hfe reading. I used the well-known Peak Atlas elements analyzer to analyze each transistors and I may clearly see the large difference between the Hfe readings of the two transistors. The original C5707 transistor has Hfe value of 379 whereas the brand new badge of the C5707 transistor has Hfe worth of 161! Ultimately I found the reply!
I did tried change the four C5707 transistors at one go with the brand new badge of transistors however the outcome was the same. Installing the transistors that have the Hfe studying of 350 to 400 solved the show shutdown problem. This circuit seem like it may well only work with the same sort of transistor that has the quite precise Hfe worth! That's why for such a Monitor circuit, many technicians hardly can find a appropriate replacement. In other phrases, even should you could get the substitution transistor which have greater Volt, Amp and Watt but different Hfe worth, you still won't have the ability to deliver the LCD Monitor back to life again. From the above take a look at, this Monitor circuit has voice out loud and clear that it solely need the same part quantity with the identical Hfe worth except you might have some related transistor substitute specification that is an identical to the unique one.
For my readers that are in this electronic repairing line, though a few of you might not be within the LCD Monitor restore, I hope you'll take up this data and apply it in your field. Who knows at some point you would have face the same drawback that I am going through and this article could easily assist you to solve your drawback fast. Have a great and a blessed day!
BenQ T705 LCD Monitor Problem in C5707 Transistor
This BenQ T705 LCD Monitor has a standard fault of display shutdown after few you "On" for few seconds. The cause of the problem was normally a shorted one or two of the C5707 push pull transistors. In addition to the shorted transistor, one additionally has to test the tuning capacitor for top ESR value with the help of ESR meter. If you do not personal one, you should utilize the digital capacitance meter to test the capacitance value. However, from my expertise, checking only the capacitance value does not guarantee that the capacitor is nice except you confirm it with ESR meter. The reason why I emphasis on checking this tuning capacitors was as a result of the capacitors have a excessive failure rate that might cause the C5707 transistor to go shorted. You even have to observe the high voltage transformer pins carefully. I had come throughout quite plenty of shorted C5707 transistors brought on by dry joints in pins of the excessive voltage transformer.
In this case, as traditional after I've confirmed that only two C5707 transistors shorted, I began to test the tuning capacitors and examine the pins of the high voltage transformer. Both the tuning capacitors found to be okay but there were dry joints within the transformer pins. Contemporary solder was utilized to the high voltage transformer pins and I'm able to "On" the LCD Monitor. Guess what? The Monitor has the identical symptom once more which is display shutdown after few seconds! I do not imagine it as most of the time it will certainly work as it is a common fault!
I started to recheck the encompassing parts which have connection to the C5707 transistors but found no faults in it. Analyzing the board many times did not reveal any improper soldering job. There have to be something that has gone flawed that had caused the LCD Monitor to shutdown. Deep in my coronary heart I don't suspect backlights drawback as a result of the C5707 transistors shorted was brought on by dry joints within the high voltage transformer. Beside, the backlights were fairly reliable for this BenQ LCD Monitor model.
Considering again, I purchased a brand new badge of C5707 transistors from my digital suppliers not long ago. The center pin (leg) is a bit shorter than the opposite two as proven from the photo below. I thought to myself would it be this badge of transistors which have drawback causing the display shutdown after few seconds? In fact I am unable to blindly suspect the transistors except I've some proof of it. The discovering begins..................
Testing the C5707 transistor with an analogue meter set to X 1 and to X 10 Ok Ohm would not seem to be it has problem. Evaluating the outcome with an original C5707 transistor did have some distinction in the X 10 K Ohm vary but the studying is acceptable from my years of experience in testing transistor. The only thing that I have never in contrast is the Hfe reading. I used the well-known Peak Atlas elements analyzer to analyze each transistors and I may clearly see the large difference between the Hfe readings of the two transistors. The original C5707 transistor has Hfe value of 379 whereas the brand new badge of the C5707 transistor has Hfe worth of 161! Ultimately I found the reply!
I did tried change the four C5707 transistors at one go with the brand new badge of transistors however the outcome was the same. Installing the transistors that have the Hfe studying of 350 to 400 solved the show shutdown problem. This circuit seem like it may well only work with the same sort of transistor that has the quite precise Hfe worth! That's why for such a Monitor circuit, many technicians hardly can find a appropriate replacement. In other phrases, even should you could get the substitution transistor which have greater Volt, Amp and Watt but different Hfe worth, you still won't have the ability to deliver the LCD Monitor back to life again. From the above take a look at, this Monitor circuit has voice out loud and clear that it solely need the same part quantity with the identical Hfe worth except you might have some related transistor substitute specification that is an identical to the unique one.
For my readers that are in this electronic repairing line, though a few of you might not be within the LCD Monitor restore, I hope you'll take up this data and apply it in your field. Who knows at some point you would have face the same drawback that I am going through and this article could easily assist you to solve your drawback fast. Have a great and a blessed day!
Print this page
No comments:
Post a Comment