Lines at top of screen - Loewe Concept 8420


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Lines at top of screen - Loewe Concept 8420

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coylum
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Apr 19, 2008, 2:50 AM

Post #1 of 11 (207 views)
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Lines at top of screen - Loewe Concept 8420	Can't Post

Hi, Horizontal lines, which appear to be modulated, have appeared at the top of the screen on my Concept 8420 (Q2000 chassis). They occupy about the top 2" of the screen. Picture is sharp and no apparent foldover.
I now have a schematic for this TV but would appreciate guidance on most likely culprit!

rrobor
Veteran

Apr 19, 2008, 4:03 AM

Post #2 of 11 (202 views)
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Re: [coylum] Lines at top of screen - Loewe Concept 8420 [In reply to]	Can't Post

It is foldover, what you are seeing is retrace lines whilst the vertical scan is trying to return to the top. that should be blacked out at the top of the scan before it starts to scan the picture. The waveform if you could see it would not be a nice sharp sawtooth, the tops would be rounding off. The modulation is teletext info. Your likely culprit is that the voltage to the vertical is low due to a capacitor dried out, usual values for filter there is from 330uF to 1000uF, but check the others in the vertical, see how much shrinkage is on the plastic or are their tops starting to bulge.

coylum
Novice

Apr 19, 2008, 8:15 PM

Post #3 of 11 (189 views)
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Re: [rrobor] Lines at top of screen - Loewe Concept 8420 [In reply to]	Can't Post

Thanks rrbobor. You describe it perfectly, particularly the teletext.
The schematic of the vertical amp can be found here: http://i147.photobucket.com/...owlermc/vertical.gif
Do you think it most likely that it is one of the electrolytics here or should I be checking further back to the main power supply?
Your help is much appreciated...

rrobor
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Apr 20, 2008, 3:29 AM

Post #4 of 11 (182 views)
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Re: [coylum] Lines at top of screen - Loewe Concept 8420 [In reply to]	Can't Post

Im sorry I dont wipe bums, read what I wrote, find out where the power for the vertical comes from. It is not good enough for someone to fix their TV and not understand. You are dealing with things that can be lethal. I am not going to spoon feed an idiot. That you are not an idiot and yet you asked that question suggests you are lazy, sorry, pick your game up. Rob.

coylum
Novice

Apr 20, 2008, 3:51 AM

Post #5 of 11 (178 views)
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Re: [rrobor] Lines at top of screen - Loewe Concept 8420 [In reply to]	Can't Post

How precious a response - definitely one to frame.....

techchris
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Apr 20, 2008, 10:26 AM

Post #6 of 11 (171 views)
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Re: [coylum] Lines at top of screen - Loewe Concept 8420 [In reply to]	Can't Post

change c561 and c563 and all will be well.

(This post was edited by techchris on Apr 20, 2008, 10:27 AM)

coylum
Novice

Apr 20, 2008, 11:42 PM

Post #7 of 11 (156 views)
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Re: [techchris] Lines at top of screen - Loewe Concept 8420 [In reply to]	Can't Post

Thanks for the response. I have changed C561 and C563 as suggested along with C574 and C578, this latter capacitor is just prior to the supply line on U27.
Sadly there is no change, the modulated lines are still there at the top of the screen although there is some variation between channels, on one channel (Channel 9 Australia) there is no sign of the problem.
The capacitors I removed had relatively low ESR's and showed no physical signs of failure.
So I guess it's back to the schematic and some logical thought! Anyway thanks again....

rrobor
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Apr 21, 2008, 6:20 AM

Post #8 of 11 (143 views)
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Re: [coylum] Lines at top of screen - Loewe Concept 8420 [In reply to]	Can't Post

Thank you. Now you are trying to think, not relying on others with the proverbial silver platter. Yes perhaps Im precious, but look to how much info I do give out. So when I want you to think is that a bad thing. Now you have done the obvious, and yet you ask another silly question, why is teletext lines not showing on all channels. Well punk have I shot six bullets or 7 bullets, or do you just gots to know. No text lines on Chan 9 guess why, or do you just gots to know. Your next change is the IC.

coylum
Novice

Apr 21, 2008, 6:28 AM

Post #9 of 11 (139 views)
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Re: [rrobor] Lines at top of screen - Loewe Concept 8420 [In reply to]	Can't Post

Please don't feel obliged to continue with your inane comments .. I won't miss you one bit.

rrobor
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Apr 22, 2008, 4:09 AM

Post #10 of 11 (90 views)
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Re: [coylum] Lines at top of screen - Loewe Concept 8420 [In reply to]	Can't Post

All I asked you to think yet you did not , you insult. There is no teletext on Channel 9 so you are still wanting someone to tell you what to do rather than understand why you are getting the results you get, then seek a bit of guidance. Your chances of repairing that TV is then slim, I advise you to get help.

coylum
Novice

Apr 22, 2008, 5:03 AM

Post #11 of 11 (87 views)
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Re: [rrobor] Lines at top of screen - Loewe Concept 8420 [In reply to]	Can't Post

I agree I need help with this issue that's why I'm here....

But I think I might be better off elsewhere.... and that's where I will go....

Please no more posts...

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