Technosonic LCD3251 picture fault


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Technosonic LCD3251 picture fault

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YARDIE
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Feb 15, 2013, 2:06 PM

Post #1 of 8 (2798 views)
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Technosonic LCD3251 picture fault	Can't Post

PC and HDMI inputs work fine producing a perfect picture but the 2 Scarts, Component jack inputs and the Ant In produce no visible picture, its very faint/distorted with green horizontal flickering/strobing lines covering the whole screen.
Change the transparency setting in the Menu to low and the distortion is less, turn up the transparency to high and the green line distortion increases. The problem appears to have something to do with the Black, possibly.
OSD displays fine regardless of which source is selected.
The rear panel is removed ready for checking/testing if one could be pointed in the right direction.
Thanks

Ifixeverything
New User

Feb 28, 2013, 8:51 PM

Post #2 of 8 (2685 views)
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Re: [YARDIE] Technosonic LCD3251 picture fault [In reply to]	Can't Post

You might try a main board swap. I had a TV with intermittent HDMI failure but PC in and RCA in would work fine, sound was always fine and the OSD menu worked perfect. New main got my digital inputs working again, just fine.

Honestly, for the time and special equipment surface mount components require to replace individually, I find it more cost effective to go with a whole new (or used) board most of the time anyway.

--------------
TV repair hobbyist, former robotics technician by trade.

YARDIE
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Feb 28, 2013, 9:10 PM

Post #3 of 8 (2681 views)
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Re: [Ifixeverything] Technosonic LCD3251 picture fault [In reply to]	Can't Post

Thanks, I believe it may be the control board at fault and shall look into the cost of replacement but thought there might be some simple checks or component level replacements that might be worth a go first, afterall the board is half buggered so what harm could I do? Completely bugger it, no real loss to be honest.
There are 2 different signals going through this board, one signal gets processed and the other does not? The signal thats being processed is obviously not being converted/scrambled properly, but is it due to a chip, beyond my repair, or is the signal reveiving interference i.e bad capacitor.

Ifixeverything
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Feb 28, 2013, 9:24 PM

Post #4 of 8 (2678 views)
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Re: [YARDIE] Technosonic LCD3251 picture fault [In reply to]	Can't Post

That does sound like noise. If you're lucky, it might be a surface mount cap...

Have you tested the SMC capacitors? You can test them with an ohm meter (multi meter). One semi-ok description is here: http://wiki.answers.com/Q/How_do_you_test_a_capacitor_using_a_multimeter

More or less, if they don't respond as the description, they're bad. Different rated caps respond differently so take note of the patterns until you're familiar with it.

--------------
TV repair hobbyist, former robotics technician by trade.

YARDIE
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Feb 28, 2013, 9:33 PM

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Re: [Ifixeverything] Technosonic LCD3251 picture fault [In reply to]	Can't Post

I don't know if this looks familiar to anyone or if its a one off, but heres a picture of the image, or lack of image I'm getting.

[URL=http://imageshack.us/photo/my-images/51/20130214011336.jpg/]

Uploaded with [URL=http://imageshack.us]ImageShack.us

YARDIE
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Feb 28, 2013, 9:59 PM

Post #6 of 8 (2672 views)
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Re: [YARDIE] Technosonic LCD3251 picture fault [In reply to]	Can't Post

I shall dig out a resistor and my DMM and try out checking those caps. I have made an ESR meter on a breadboard but not sure its working 100% so shall compare the results from both methods.
Thank-you

YARDIE
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Mar 2, 2013, 4:40 PM

Post #7 of 8 (2645 views)
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Re: [YARDIE] Technosonic LCD3251 picture fault [In reply to]	Can't Post

I have found a service manual for what appears to be the same tv but branded differently but still need help diagnosing fault.

Get the same picture on tv as above with S-Vhs input too!
I feel the fault is going to lay somewhere to do with video signalling, something along the lines of PC and HDMI do not need as much video processing as Scart and Component inputs and so the circuitry dealing with these inputs is somehow not properly processing the signal.
Perhaps someone could try and run through some checks with me to troubleshoot, I have a DMM, cap meter (out of circuit) and and old oscilloscope but where to put those probes.
Thanks

YARDIE
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Mar 18, 2013, 3:58 PM

Post #8 of 8 (2600 views)
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Re: [YARDIE] Technosonic LCD3251 picture fault [In reply to]	Can't Post

So does anyone know how to 'test'/check a TW9906 Comb filter video decoder and associated clock generator?

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