HP Pavilion vf15 (15" Flat Panel LCD Monitor). Yes, I know it's ancient and has a far lower resolution than modern phone screens but it is nonetheless an LCD monitor that I'm working on. Also, my repair attempt is not a hopeless quest to delay purchasing a new monitor (I'm quite proud of my full-HD dual-monitor setup on the same desk, different PC). So you could say this is a journey that is mostly educationally motivated and partially sentimentally motivated. Here's the whole story:
So, for a while, the screen did this "flashing" thing where it would (upon being awoken by a PC) “flash” the signal image for much less than a second then go black for about 4 second then flash again etc. etc. It did this back and forth indefinitely. I couldn't even turn the screen off unless I unplugged it from the wall or pressed the power button at the exact instant that the image flashed. I also discovered that I could turn off the screen this way (using the power button with perfect timing), wait 15 seconds for the computer to finish booting (or waking up), then turn it on when the video signal stabilized and it would display as it should - no problems. It behaved identically with multiple PCs. I had always assumed that there was a bad capacitor or two, just based on my intuition of circuits.
Anyways, the monitor recently died completely, no flashing, no green LED, nothing. I took it as a challenge! I did a lot of research (yes, I did indeed read about this extensively before posting), and confirmed my capacitor theory. I took the whole thing apart and located the bad caps. I ordered some new ones of the same specs and replaced them (see pics).
Based on my research and the bad condition of capacitors I found, I'm certain that the caps were an issue and probably caused the screen flashing. However, the screen still does not turn on (no green LED either). Here's the fun part: there's a quiet clicking sound like a clock when power is supplied to the board. Looking into the power supply is the next obvious step of course. Further research (including threads on this site) of this clicking noise has pointed me directly to the power supply transistors. There are two transistors on this board (see pics).
I know that the codes on transistors are proprietary, so these may be useless to you, but here are the numbers that are written on each one:
C5706 4F
C5706 4G
I feel comfortable soldering and whatnot. But I don't know a whole lot about transistors. I know what they do but I've never needed to replace any. The methods of testing transistors that I found online seemed kinda sketchy to me. I don't know how to pick which transistors to buy to replace these. I know current ratings are important. I'd assume there are voltage ratings and a few other specs too… I just don't know the specific specs of these transistors. Also, what do the 4F and 4G mean? Do these transistors have different specs? Searches of these part numbers yielded a few data sheets of transistors but they did not end in 4F or 4G (they had other random letters). How do I make sure that I buy transistors that will work for this system? Any help is appreciated. Also, is there any other part that could cause the power supply to make soft clicking sounds? The fuse is good. If you need me to check or test any other components just let me know.
For the sake of communication you should know a few things. I'm an engineer. Sorry to drop the “I'm an engineer card,” I know it can be annoying to some people. I just say it so that you know that I'm not just a kid in a garage and that I do understand technical terms. I'm obviously not an electrical engineer, but I've had some formal training with circuits and signal analysis so electrical and computer science topics are things that I can understand if you explain them to me. I do have a multimeter and soldering equipment.
So, for a while, the screen did this "flashing" thing where it would (upon being awoken by a PC) “flash” the signal image for much less than a second then go black for about 4 second then flash again etc. etc. It did this back and forth indefinitely. I couldn't even turn the screen off unless I unplugged it from the wall or pressed the power button at the exact instant that the image flashed. I also discovered that I could turn off the screen this way (using the power button with perfect timing), wait 15 seconds for the computer to finish booting (or waking up), then turn it on when the video signal stabilized and it would display as it should - no problems. It behaved identically with multiple PCs. I had always assumed that there was a bad capacitor or two, just based on my intuition of circuits.
Anyways, the monitor recently died completely, no flashing, no green LED, nothing. I took it as a challenge! I did a lot of research (yes, I did indeed read about this extensively before posting), and confirmed my capacitor theory. I took the whole thing apart and located the bad caps. I ordered some new ones of the same specs and replaced them (see pics).
Based on my research and the bad condition of capacitors I found, I'm certain that the caps were an issue and probably caused the screen flashing. However, the screen still does not turn on (no green LED either). Here's the fun part: there's a quiet clicking sound like a clock when power is supplied to the board. Looking into the power supply is the next obvious step of course. Further research (including threads on this site) of this clicking noise has pointed me directly to the power supply transistors. There are two transistors on this board (see pics).
I know that the codes on transistors are proprietary, so these may be useless to you, but here are the numbers that are written on each one:
C5706 4F
C5706 4G
I feel comfortable soldering and whatnot. But I don't know a whole lot about transistors. I know what they do but I've never needed to replace any. The methods of testing transistors that I found online seemed kinda sketchy to me. I don't know how to pick which transistors to buy to replace these. I know current ratings are important. I'd assume there are voltage ratings and a few other specs too… I just don't know the specific specs of these transistors. Also, what do the 4F and 4G mean? Do these transistors have different specs? Searches of these part numbers yielded a few data sheets of transistors but they did not end in 4F or 4G (they had other random letters). How do I make sure that I buy transistors that will work for this system? Any help is appreciated. Also, is there any other part that could cause the power supply to make soft clicking sounds? The fuse is good. If you need me to check or test any other components just let me know.
For the sake of communication you should know a few things. I'm an engineer. Sorry to drop the “I'm an engineer card,” I know it can be annoying to some people. I just say it so that you know that I'm not just a kid in a garage and that I do understand technical terms. I'm obviously not an electrical engineer, but I've had some formal training with circuits and signal analysis so electrical and computer science topics are things that I can understand if you explain them to me. I do have a multimeter and soldering equipment.
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