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Author Topic: Neotec NT-500 Vertical doesn't fill screen  (Read 425 times)

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MrArcade

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Neotec NT-500 Vertical doesn't fill screen
« on: July 05, 2019, 04:50:58 pm »
This NT-500 is in an older buck hunter. It had hv but a very dark picture that seemed out of frequency'ish. I found 4 definitely bad caps: C521, C744, C722, C722a and replaced them.

Now I have a nice bright picture but the picture doesn't fill the screen vertically. There is a black bar at the bottom of the screen. When I try to adjust with the digital adjustment I get vertical fold-over at the bottom with the same 2" black bar.

Am I looking for bad electrolytic caps in the vertical section? If so, which caps? I have a schematic but am not sure which area controls vertical.

Thanks as always!
Oh, the memories of living on pizza subs and Dr Pepper...

MrArcade

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Re: Neotec NT-500 Vertical doesn't fill screen
« Reply #1 on: July 09, 2019, 03:55:59 pm »
Replaced C907, C305, C325, and C601. Seems to fill screen vertically now. Pretty sure C305 (25v 470uf) was the main culprit. Doing esr test it should have pegged the needle (near 0) but it measured around 3.
« Last Edit: July 11, 2019, 02:10:39 pm by MrArcade »
Oh, the memories of living on pizza subs and Dr Pepper...

lilshawn

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Re: Neotec NT-500 Vertical doesn't fill screen
« Reply #2 on: July 09, 2019, 08:04:46 pm »
check and or replace R623/R623A these supply power for the verticacl deflection IC. if they start going out of wack, the resistance goes up and the voltage driving the IC chip goes down...causing wierd foldover and size issues. a failed C325 can load it down enough that the resistors start to burn up and go out of spec.

it could be that the IC is going south too. I've seen them partially fail, partially work...doing wierd foldover and size issues too... it's a TDA8172.... I buy them in packs of 25 they go so often.

check you resitors first though.

MrArcade

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Re: Neotec NT-500 Vertical doesn't fill screen
« Reply #3 on: July 11, 2019, 02:11:33 pm »
Thanks!
Oh, the memories of living on pizza subs and Dr Pepper...