Re: Has anyone seen this defect before?
Interesting. Too much pressure from the back or from the front? Does this mean the panel is terminally broken? Thanks...
shikuru
Member
Last Activity: 09-08-2018, 01:07 PM
Joined: 12-12-2011
Location: Hamburg
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Has anyone seen this defect before?
Hello everyone, I've never seen something like this before. The spot is pixel-wide. Is this still fixable or is the panel a goner? Thanks... -
Re: Samsung Syncmaster 245BW
Great guys, thanks. Profile was updated
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Re: Samsung Syncmaster 245BW
Can I replace the big 82uF cap with a similar voltage, but bigger capacitance? Those 82uF are pretty hard to get around here. Would 100uF or even 220uF work? ThanksLeave a comment:
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Re: Vestel 17PW20 intermittent backlight
Should not R817-R819 give 620kOhm each, even when measured in circuit (and not overload on my multimeter)?Leave a comment:
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Re: Vestel 17PW20 intermittent backlight
I re-checked. It definitely has only 333.9V (@150uF just as you said). It also discharges fully in less than a minute after power is gone.Will do, didn't have the schematics at hand today.
Let's hope not. Those are hella hard to detect. It may well be though, since I can make the problem appear/vanish with a hairdryer.
Another question: Shouldn't there be 5V in standby? I get 0.5V on some lines (just as I mentioned) but never 5V. Same when running.
PS. I really enjoy this. Thanks for all the hints and...Leave a comment:
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Re: Vestel 17PW20 intermittent backlight
Yes, but they seemed to be working. I tested with cap meter. So I went and put an entire reliability kit. Only the 220uF was broken (C817). After fitting the reliability kit, the output voltage did increase from 22.3 to 24.3V though.I might try it. I do measure about 339V across its pins though. That should be about right.
I am thinking it might also be the inverter. It does make a loud buzzing noise. And upon thinking about it: When using the hairdryer, hot air also got to the inverter. So what I would really like to know is...Leave a comment:
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Re: Vestel 17PW20 intermittent backlight
So that might just be the reason I did not measure 2.5V!!!
I am really discouraged at the moment. The problem did not go away despite my fixing the bad cap. I think for any additional steps I would need an Oscilloscope, which I do not have
The original issue still appears. After warming up, the backlight flashes on/off, when there is a lot of white in the picture.
Could this be inverter-related? Does the main logic regulate backlight brightness according to how much white there is in the picture?...Leave a comment:
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Re: Vestel 17PW20 intermittent backlight
Thanks about the hint with the coil. A friend has a 78L05 at hand so I am replacing it just to be sure.
Do I need to worry about the 2.5V line being at 0.5V?Leave a comment:
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Re: Vestel 17PW20 intermittent backlight
Some perceptions after the replacements: The inverter gives a loud buzz, so does the smaller of the transformers on the 17pw20 (the one near the mains input). Everything appears to be working.
What is really worrying me though is that the 2.5 supposed Volts are actually more like 0.5 Volts. I am measuring them on the connectors.Leave a comment:
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Re: Vestel 17PW20 intermittent backlight
So I've replaced the aforementioned components today. All tested fine in my multimeter, except the 220nF electrolytic capacitor C817. I did not replace the 78L05 voltage regulator as I did not have a spare.
Tom66, should I replace any additional components considering my particular fault? Can I let the 78L05 be, or must it be exchanged. It's pretty close to the broken capacitor on the board...
Thanks
Oh one more thing: There's an error up there. C901 should be 4,7uF 50V, not 3,3 uF.Leave a comment:
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Re: Vestel 17PW20 intermittent backlight
I was surprised as well. I used an old C64 to get a white background image to trigger the fault, together with the hairdrier.
Damn, I didn't read your post until after ordering with my component seller of choice. But I suppose the total price is about the same.
For general purposes, here are the components and values contained in the repair kits for the 17PW20.1:
IC829 - 78L05 (if on board)
Q809 - BC337 (if on board)
C877 - 15nF 1600V
C878 - 15nF 1600V
C817 - 220uF 25V
...Leave a comment:
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Re: Vestel 17PW20 intermittent backlight
Tom66: OK it seems you were spot on. I heated C878 and C877 with a hairdryer and off it went. Then, a short while after it cooled down, all is fine again. I do not detect a voltage drop at the 24V line during the flickering, but I suppose this is because my Voltmeter isn't quick enough to detect it.
Now, with the replacement of those caps, would you recommend to replace any other components while I have the TV open?
Thanks again mate!!!Leave a comment:
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Re: Vestel 17PW20 intermittent backlight
Thanks tom66. Will check. In the meantime, some additional perceptions:
The big mains capacitor carries a mere 225 Volts. The 24V line carries 23 volts, no more. It goes down to 22.8 after several minutes in operation.
Edit: Nope, the backlight will shut off entirely. Also, with an open case, I cannot seem to reproduce the fault. Perhaps it's bad solder lines. I cannot find 15n capacitors. Do you mean C878 and C877? They are shown as 12n in the schematics? Or perhaps C834 and C835 which are shown as 33n in the schemati...Last edited by shikuru; 12-12-2011, 03:40 PM.Leave a comment:
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Vestel 17PW20 intermittent backlight
I have a strange problem with a Vestel chassis (Luxor LCD 328). When there is a lot of white in the picture, the backlight will start a very quick flickering. It will recover itself once the picture changes but reappear every time there is a certain amount of white space in the picture.
When the picture drops it will flicker on/off very quickly. It looks as if the whole backlight gets shut off.
Do you have any pointers? Could the PSU be the culprit? Thanks
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