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Challenge in C5707 Transistor in BenQ T705 Liquid crystal display Check

This BenQ T705 Liquid crystal display Keep track of provides a frequent fault of screen shutdown following several you “On” for number of seconds. The reason for the condition was ordinarily a shorted one or two from the C5707 push pull transistors. Other than the shorted transistor, a person also should check the tuning capacitor for top ESR value along with the support of ESR meter. In case you tend not to own 1, you can utilize the electronic capacitance meter to check the capacitance price. However, from my practical experience, checking only the capacitance worth will not guarantee the capacitor is sweet until you verify it with ESR meter. The explanation why I emphasis on checking this tuning capacitors was because the capacitors have a superior failure level that can cause the C5707 transistor to go shorted. You also really have to notice the high voltage transformer pins cautiously. I had come across fairly a number of shorted C5707 transistors induced by dry joints in pins with the large voltage transformer;Direct Components Inc.

In such cases, as common following I’ve confirmed that only two C5707 transistors shorted, I started to check the tuning capacitors and verify the pins from the substantial voltage transformer. Both the tuning capacitors located to be okay but there were dry joints from the transformer pins. Refreshing solder was utilized for the higher voltage transformer pins and i am all set to “On” the Lcd Keep track of. Guess what? The Watch has precisely the same symptom yet again that is screen shutdown soon after handful of seconds! I don’t think it as the vast majority of time it is going to undoubtedly do the job as that is a common fault!

I started to recheck the surrounding factors which have link towards the C5707 transistors but uncovered no faults in it. Analyzing the board many times did not expose any improper soldering career. There will have to be a little something which has gone incorrect that had triggered the Liquid crystal display Observe to shutdown. Deep in my coronary heart I do not suspect backlights difficulty for the reason that the C5707 transistors shorted was brought about by dry joints inside the substantial voltage transformer. Beside, the backlights had been very reputable for this BenQ Lcd Observe product.

Contemplating again, I purchased a whole new badge of C5707 transistors from my digital suppliers not extended in the past. The middle pin (leg) is often a little bit shorter compared to the other two as proven from the photograph under. I thought to myself would it be this badge of transistors that have problem leading to the display screen shutdown after couple seconds? Needless to say I can’t blindly suspect the transistors except I have some evidence of it. The getting starts………………

Tests the C5707 transistor by having an analogue meter established to X 1 and to X ten K Ohm will not appear to be it’s got problem. Evaluating the result with the primary C5707 transistor did have some difference inside the X ten K Ohm selection but the looking through is suitable from my decades of practical experience in testing transistor. The only thing which i haven’t in contrast may be the Hfe studying. I made use of the famous Peak Atlas factors analyzer to analyze the two transistors and that i could obviously begin to see the massive distinction between the Hfe readings of your two transistors. The first C5707 transistor has Hfe price of 379 whilst the new badge in the C5707 transistor has Hfe worth of 161! Finally I discovered the solution!