Digital Monitor Meter
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US $161.99
Setting Up The Transistors Which Have The Hfe Studying Of 350 To Four Hundred Solved The Display Shutdown Dilemma
I began to recheck the surrounding elements which have connection towards the C5707 transistors but found no faults in it. Examining the board many times didn't reveal any incorrect soldering task. There should be some thing which has gone wrong that had triggered the LCD Monitor to shutdown. Deep in my heart I don't suspect backlights issue due to the fact the C5707 transistors shorted was brought on by dry joints in the large voltage transformer. Beside, the backlights had been quite reliable for this BenQ LCD Monitor model.
Considering back again, I purchased a new badge of C5707 transistors from my electronic suppliers not long in the past. The middle pin (leg) is actually a bit shorter compared to other two as shown from your image under. I thought to myself would it be this badge of transistors that have dilemma leading to the display shutdown following couple of seconds? Obviously I can't blindly suspect the transistors unless of course I have some proof of it. The locating begins..................
Testing the C5707 transistor having an analogue meter set to X one and also to X 10 K Ohm doesn't appear like it's got challenge. Comparing the outcome having an original C5707 transistor did have some difference within the X 10 K Ohm array but the studying is acceptable from my many years of encounter in testing transistor. The sole thing that I have not in comparison is the Hfe studying. I utilized the well-known Peak Atlas components analyzer to assess both transistors and I could obviously see the massive distinction in between the Hfe readings with the two transistors. The original C5707 transistor has Hfe worth of 379 although the new badge of the C5707 transistor has Hfe worth of 161! At last I discovered the solution!
I did tried substitute the four C5707 transistors at one go using the new badge of transistors but the result was the same. Installing the transistors that have the Hfe studying of 350 to four hundred solved the display shutdown predicament. This circuit appear like it might only function using the very same type of npn transistor that has the quite precise Hfe worth! That's why for this kind of Monitor circuit, several technicians barely can uncover a appropriate replacement. In other words, even if you could obtain the substitution transistor that have higher Volt, Amp and Watt but several Hfe worth, you nonetheless won't be able to deliver the LCD Monitor back again to existence again.
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