I intended to ask for help but in course of making a writing it down I have actually succeeded in repairing this damn thing. If because of that this post doesn't belong to this section, then I'm sorry and feel free to move it somewhere else (, mods).
I am going to describe the course of repairing it for your further reference. It weren't just bad caps.
So first I received this monitor (or rather a TV set) non working. Opening it revealed that someone had already tampered with it - the caps were manualy soldered and one had been bodged of two caps in series. I replaced them with some LowESR ones, but I weren't certain about their ratings. I ended up with:
2 x 820u in the inverter part and
47u small one closest to the AC input
330u lonely one in the group of 3 near corner
670u instead of 2 x 330u. They are actually in parallel, and I haven't 330u's handy. 2 x 670u work as well.
which seems to be more or less the values you can find on these power supply boards.
So here the quest begins. The device now had been lighting blue power LED on for about 3 seconds, while not responding to buttons and screen still dark. That was quite a surprise. I had taken a closer look with my ears. It was making a noise during the first few seconds while the LED was lit and then was going silent. I assumed it was trying really hard to power up the HV circuitry (inverters), so I decided to replace SOP8 dual N/P chanel mosfets STM8*** with IRF7319. I didn't bother checking if they were actually broken, though while desoldering and leveraging pins with a pin, two pins just fell off - a bit too easily. Enough to say that this had not solved the problem. So further down I turned on my scope - mosfets were not being driven -> so what does inverter IC -> its chip ENable stayed low ! So I cut the EN wire coming from logic board, bridged IC's EN to positive, and.. It worked. Yeah, sort of, because backlight stayed on all the time.
At this point I was happy with the result, but decided to track the signal down into the mysterious area of the logic board. And that signal was there. It turned out, that logic board was driving EN line correctly. So what happened ? You are not aware of one step which I skipped: I desoldered some 100u cap because it obstructed tracking the trace down. And this damn cap had shorted, connecting EN to ground in a shortsolid way. Now works like a charm. (more like a 2007 charm)
I find this experience very instructive (especially judging by the noise) and I hope, that if you made it that far, you find my story somehow enjoyable (:
Never trust them caps
Images:
-showing logic board and the bad cap
-after bodging new one. (I ripped a pad off..)
Final thought: I don't really understand why monitor decited to turn off upon failure in turning backlight on ..
I am going to describe the course of repairing it for your further reference. It weren't just bad caps.
So first I received this monitor (or rather a TV set) non working. Opening it revealed that someone had already tampered with it - the caps were manualy soldered and one had been bodged of two caps in series. I replaced them with some LowESR ones, but I weren't certain about their ratings. I ended up with:
2 x 820u in the inverter part and
47u small one closest to the AC input
330u lonely one in the group of 3 near corner
670u instead of 2 x 330u. They are actually in parallel, and I haven't 330u's handy. 2 x 670u work as well.
which seems to be more or less the values you can find on these power supply boards.
So here the quest begins. The device now had been lighting blue power LED on for about 3 seconds, while not responding to buttons and screen still dark. That was quite a surprise. I had taken a closer look with my ears. It was making a noise during the first few seconds while the LED was lit and then was going silent. I assumed it was trying really hard to power up the HV circuitry (inverters), so I decided to replace SOP8 dual N/P chanel mosfets STM8*** with IRF7319. I didn't bother checking if they were actually broken, though while desoldering and leveraging pins with a pin, two pins just fell off - a bit too easily. Enough to say that this had not solved the problem. So further down I turned on my scope - mosfets were not being driven -> so what does inverter IC -> its chip ENable stayed low ! So I cut the EN wire coming from logic board, bridged IC's EN to positive, and.. It worked. Yeah, sort of, because backlight stayed on all the time.
At this point I was happy with the result, but decided to track the signal down into the mysterious area of the logic board. And that signal was there. It turned out, that logic board was driving EN line correctly. So what happened ? You are not aware of one step which I skipped: I desoldered some 100u cap because it obstructed tracking the trace down. And this damn cap had shorted, connecting EN to ground in a shortsolid way. Now works like a charm. (more like a 2007 charm)
I find this experience very instructive (especially judging by the noise) and I hope, that if you made it that far, you find my story somehow enjoyable (:
Never trust them caps
Images:
-showing logic board and the bad cap
-after bodging new one. (I ripped a pad off..)
Final thought: I don't really understand why monitor decited to turn off upon failure in turning backlight on ..
Attached Files
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