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Author Topic: Neotec nt-500dx Horizontal image issues collapsing  (Read 563 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.

frankrizzo2

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #7 on: January 30, 2019, 04:22:35 pm »
Thanks for the advise. I will pull the chassis out again and take a look at those components. I tried the freeze spray on the chassis in a few different places and it didn't have any effect at all on the screen. I was really hoping to isolate the problem area with the freeze spray and shotgun a couple of components but it doesn't look like it will be that easy. It's frustrating because the problem shows up only after it is warmed up so more than likely the components are going to be within spec with it cooled down, correct?

frankrizzo2

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #8 on: January 31, 2019, 12:42:41 am »
Update: I found a cap out of spec at c523 I believe and replaced it hoping that would be the end to my problems but still the same. At least now it doesn't have to warm up for the problem to be present so it should be easier to find the faulty component. I'll try more tmw.

frankrizzo2

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #9 on: January 31, 2019, 05:19:11 pm »
Okay now that I've had a chance to test the voltages. I'm getting 11.5v at VCC at IC601. I am coming up with 14.5v going into LM7812 so I went back further in the circuit and at c551 it reads 14.5 and every cap past that all the way to LM7812 is reading the same. Where does this voltage start from? So is the issue in one of those caps or is there something on the primary side that controls that voltage?

frankrizzo2

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #10 on: February 01, 2019, 08:53:35 pm »
Anyone have any idea what the B+ is supposed to be at on these? I've replace all the caps c530, c532, c501, c505, c544, c623, c607, and c601 and I'm getting the same 14.5v reading and it looks like its supposed to be at 15.5v. All the other voltages are low at around the same percentage too so I'm wondering if it's something on the Primary side that needs replacement or adjustment? Any thoughts?

grantspain

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #11 on: February 02, 2019, 07:15:26 am »
i seriously doubt that difference will cause any issues, what you have is a component in the vertical circuit breaking down and this will be very hard to find. It could be a leaky diode or a resistor and the only way you will find it is by shotgunning the vertical circuit

frankrizzo2

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #12 on: February 02, 2019, 06:40:38 pm »
Thanks for the reply Grant. I did adjust the B+ up to 140v as that was down under where is is suppose to be and that corrected the rest of my voltages. Its just finding the problem for what is causing the monitor to act up. So you are thinking it some other component in the vertical circuit. The only thing that sucks with shotgunning resistors and diodes is that there are a ton of them and don't they have to have at least one leg out of circuit to test them correctly? Is there an easier way to test these components? I have an ESR so at least I can test Capacitors in circuit but the others are a little more difficult for me. I guess I'll just have to run through that part of the circuit and see what I find.

grantspain

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #13 on: February 02, 2019, 07:12:18 pm »
does the chassis now show this issue permanently or appears after a short time?

frankrizzo2

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #14 on: February 02, 2019, 11:14:15 pm »
It's permanent now. I let it run the other day for about an hour before I hit it with Freeze Spray but there was no reaction at all with the spray so thats when I proceeded with replacing the caps on the 15v circuit all the way to the IC TDA8172.

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Re: Neotec nt-500dx Horizontal image issues collapsing
« Reply #15 on: February 03, 2019, 05:38:27 am »
the fault will be easier to find than before, check all resistor values in vertical circuit using the schematic as a reference- any that do not read correctly lift one side from circuit and read again. Do the same with diodes