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Author Topic: Neotec nt-500dx Horizontal image issues collapsing  (Read 129 times)

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frankrizzo2

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Neotec nt-500dx Horizontal image issues collapsing
« on: January 06, 2019, 07:10:15 pm »
I have a Neotec nt-500 monitor that I did a cap kit on a couple years ago because I was starting to get some collapse and its been working great up until last night. After the machine was on for around 5-10 min it started with some horizontal collapse in the middle area of the screen. This monitor probably has 50 hrs on a cap kit with no issues. Is it common to have a cap go bad that quickly or should I be looking for other issues? Thanks

lilshawn

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #1 on: January 06, 2019, 09:47:48 pm »
try changing that caps around IC301 (TDA8172) C323 C305 etc...  if it still does it...vertical deflection IC is going south and will soon fail. replace it.

a guy with a site UTSOURCE is a pretty reliable source for these kinds of chips. I've ordered from them a few times and never had a problem with failures or fakes. he sells stuff on ebay under a few different stores as well. you can pick him put cause his chips are all displayed on a pink anti static foam.

https://www.ebay.ca/itm/10PCS-TDA8172-Encapsulation-ZIP-7-TV-VERTICAL-DEFLECTION-OUTPUT-CIRCUIT/380926387063?hash=item58b0fb6377:g:sQUAAOSwhqhaAEcN:rk:7:pf:0

frankrizzo2

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #2 on: January 06, 2019, 11:37:23 pm »
Thanks for the info! I've got the chassis pulled and was checking for cold joints because it takes some time and has to warm up before it starts doing that but I haven't been able to find anything. I will start testing those capacitors and see what I can find and possibly order that ic if I can't find any bad caps

frankrizzo2

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #3 on: January 07, 2019, 12:16:39 am »
I replaced the caps in the chassis around ic 301 but when I test the ones I pulled with an esr meter they all test good. I'll try to put the chassis back in the morning and see if there is any improvement and if not I'll order the IC

frankrizzo2

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #4 on: January 07, 2019, 10:04:15 pm »
No improvement with the caps. I'll order the IC and see if that does anything for me. I also went over everything on the board with a magnifier and touched up any solder joints that were questionable.

frankrizzo2

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #5 on: January 18, 2019, 06:42:06 pm »
So installed a new vertical IC and after it warms up I'm getting the same issue. Just need to order some freeze spray and see if I can figure out problem area. Should I be looking at any of the resistors or the orange colored capacitors around the 300 area of the board too?

lilshawn

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #6 on: January 20, 2019, 06:05:30 pm »
typically those small ceramic caps don't go out of spec they typically fail shorted. basically if not shorted... they are fine.

check r623/r623a they sometime get out of spec. (5.6 ohms...2.8 ohms together)

check your VCC into IC601 (around 12v) and R631 (10 ohms) and C623/c607/c601  this chip is where your sync pulses to drive IC301 come from. if the chip is flipping out due to dirty power, the sync will be wonky too.

 may as well replace the caps everything downstream from D510 since this is your 15/12 volt rail that powers the vertical circuit powers thos 2 IC's as well... make sure these voltage of the 15v going into the LM7812 is AT LEAST 15 volts. under ~14.5 volts, the 7812 regulator starts doing weird things.

  
 

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