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Author Topic: Neotec nt2700n help  (Read 496 times)

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djsniperwolf

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Neotec nt2700n help
« on: February 28, 2017, 01:22:38 pm »
I Think I blew the HOT. I Pulled it from the board and it is showing a short.

I see a bit of a discrepancy in the HOT that this board calls for. The board currently has a 2Sc5144, but the manual calls for a BU4530AL.

I tried another 2SC5144 that is testing as good, but when I turn on the monitor it begins to click and that HOT arcs. You can see it emit a flash for each click. What can cause this?  Thanks!
« Last Edit: February 28, 2017, 08:29:53 pm by djsniperwolf »

djsniperwolf

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Re: Neotec nt2700n help
« Reply #1 on: February 28, 2017, 08:30:24 pm »
Can someone provide me a bit of insight?

lilshawn

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Re: Neotec nt2700n help
« Reply #2 on: February 28, 2017, 09:17:35 pm »
just because they "Test" as good, doesn't mean that actually are. HOT's run at very high voltage and very high amperage. the tiny voltage a tester uses to test with is not enough to determine if it's good or not.

the only real way to know for sure is to buy a new known good HOT and use that.

the BU #'s are a philips branded part number. the 2SC #'s are universally accepted part numbers.

either part should perform equally well... there are slight differences between the BU and 2SC parts, but whether or not these differences come into play in this circuit, i don't know. i'm not an electronic engineer.

if the schematic spec'd a BU4530AL, i'd try and source a BU4530AL, otherwise if it ran forever with a 2SC5144 and it's cheaper to get than the BU, then i suppose, i'd go with that.

also, i'm not 100% sure, but quite often with these HOT's, the tab must be electrically isolated from the heatsink (silicone pad, insulted screws) if it's arcing it's shorting to the heatsink. there could be a hole or a burr on the HOT that has penetrated the silicone pad and causing it to arc through. when i'm installing a transistor, i'll use a flat block with fine grit sandpaper on it (600 grit) to burnish down the backside of the transistor. not only does it make it flat, but will eliminate any flashing or burrs on the back that might short out. quite often the molded plastic sticks out and causes the metal plate to not sit against the heatsink and dissipate heat properly.

djsniperwolf

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Re: Neotec nt2700n help
« Reply #3 on: February 28, 2017, 09:46:29 pm »
The insulated screw seemed interesting. So... I removed the screw from the HOT and fired up the monitor. It has life again! Thank you!

My question is, the HOT had never arced with the same screw in it prior to me blowing it. Where could I obtain an insulated screw?

So odd that this problem came up after I swapped out the hot.

ed12

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Re: Neotec nt2700n help
« Reply #4 on: February 28, 2017, 10:03:55 pm »
not really
did u put the insulation mica back in.?
it goes between the transistor and the heat sink
also is the hole where the screw goes through isolated ?
ie is there plastic around it or is it solid steel hole ?

ed
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djsniperwolf

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Re: Neotec nt2700n help
« Reply #5 on: February 28, 2017, 10:10:13 pm »
Mica is back in place. Also applied silicon based heat compound to both sides. The hole is steel with no insulation.

When the screw is in place, it begins to arc. Without the screw, the monitor turns on with no problem.

ed12

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Re: Neotec nt2700n help
« Reply #6 on: February 28, 2017, 10:15:16 pm »
i would expect so
u will want to find a plastic transistor washer and drill the hole to take a #32 bolt and nut
or a #38 either will do the job
the plastic transistor isolator (washer)
can be had at any electronic parts store
comes in a kit with a new mica (i suggest u use the full kit)
DO NOT RUN THAT CHASSIC UNTIL U GET THE HOT TRANNIE MOUNTED RIGHT or u will risk over heating and it failing

ed
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ed12

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Re: Neotec nt2700n help
« Reply #7 on: February 28, 2017, 10:29:52 pm »
this will help u along your way

ed
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lilshawn

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Re: Neotec nt2700n help
« Reply #8 on: February 28, 2017, 11:12:54 pm »
the 5144 should be all isolated like so:



if your screw causes it to short, i'd look into the insulator sheet having a hole in it. the transistor being smashed down on it is allowing the gap to be pressed small enough to arc.

ed12

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Re: Neotec nt2700n help
« Reply #9 on: February 28, 2017, 11:28:55 pm »
yes that is an isolated trans
but i asked the op that exact question
reply was metal..
hence my follow ups
as that is a isolated through hole transistor

ed
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djsniperwolf

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Re: Neotec nt2700n help
« Reply #10 on: March 01, 2017, 02:22:29 am »
the 5144 should be all isolated like so:



if your screw causes it to short, i'd look into the insulator sheet having a hole in it. the transistor being smashed down on it is allowing the gap to be pressed small enough to arc.

It's weird because the mica pad seems to be perfectly fine. I have also swapped it out with the thin clear plastic cover. I am not sure where the transistor is making contact to short through the screw like that. It is when the screw is making contact with the chassis, it starts arcing.

djsniperwolf

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Re: Neotec nt2700n help
« Reply #11 on: March 01, 2017, 02:30:14 am »
i would expect so
u will want to find a plastic transistor washer and drill the hole to take a #32 bolt and nut
or a #38 either will do the job
the plastic transistor isolator (washer)
can be had at any electronic parts store
comes in a kit with a new mica (i suggest u use the full kit)
DO NOT RUN THAT CHASSIC UNTIL U GET THE HOT TRANNIE MOUNTED RIGHT or u will risk over heating and it failing

ed

This seems to be an option. Prior to changing the HOT, this had never occurred which is why I am so confused. Thanks for the help so far.

djsniperwolf

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Re: Neotec nt2700n help
« Reply #12 on: March 01, 2017, 06:19:50 pm »
Man this monitor... So I ported out the frame hole to prevent screw contact. Seemed to work great.

But now, I heard some kind of arcing, whenever it would occur the screen would roll, artifact, and display odd problems. I look in the back and I see that the focus wire connected to the neckboard is slightly arcing within the plastic cover. It ultimately took out my HOT again.

This is what most likely cause the first HOT to blow. Anything I should check/do?  Thanks.

lilshawn

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Re: Neotec nt2700n help
« Reply #13 on: March 01, 2017, 06:43:25 pm »
I look in the back and I see that the focus wire connected to the neckboard is slightly arcing within the plastic cover. It ultimately took out my HOT again.

This is what most likely cause the first HOT to blow. Anything I should check/do?  Thanks.

this. arcing causes huge fluctuations in voltage. you either have an issue with the crt socket or an internal fault in the flyback causing the focus to go HV and arc.

how does the flyback look? any cracks around the knobs or the casing?

djsniperwolf

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Re: Neotec nt2700n help
« Reply #14 on: March 01, 2017, 07:47:21 pm »
Flyback looks great. I think I may have found the cause, what do you think? If so, any idea of where to get a replacement socket?

lilshawn

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Re: Neotec nt2700n help
« Reply #15 on: March 01, 2017, 10:49:45 pm »
the socket looks okay, unless i'm missing something. it's not cooked or overly splayed out. not seeing any tracking evidence of arc getting out.

it would be helpful if you could narrow down a little more where you saw the arc flash. i'm thinking your issue could be a little further down in the box part where the focus lead goes in. the socket may have integral spark gaps to prevent catastrophic failure in the event HV comes out of the focus.

the socket/board will have integral spark gaps so if a certain threshold is reached it will arc over. the focus lead is actually part of the high tension (25,000 some odd volts on the anode lead) it has some resistors and diodes in line to very rudely step down the voltage... if some of those components are failed/failing, it can cause the focus lead to go high and arc.

ed12

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Re: Neotec nt2700n help
« Reply #16 on: March 01, 2017, 10:53:53 pm »
correct
which in turn will cook your flyback

ed
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djsniperwolf

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Re: Neotec nt2700n help
« Reply #17 on: March 02, 2017, 11:37:21 pm »
the socket looks okay, unless i'm missing something. it's not cooked or overly splayed out. not seeing any tracking evidence of arc getting out.

it would be helpful if you could narrow down a little more where you saw the arc flash. i'm thinking your issue could be a little further down in the box part where the focus lead goes in. the socket may have integral spark gaps to prevent catastrophic failure in the event HV comes out of the focus.

the socket/board will have integral spark gaps so if a certain threshold is reached it will arc over. the focus lead is actually part of the high tension (25,000 some odd volts on the anode lead) it has some resistors and diodes in line to very rudely step down the voltage... if some of those components are failed/failing, it can cause the focus lead to go high and arc.

It looked to be sparking from inside of the white focus wires mini plastic encasement. I opened it up to find that the wire is still indeed connected. I do not see any charring or scorching from this happening.

Could this be from a possible faulty flyback, or maybe the B+ being set too high? As far as diodes and resistors, would I be checking the ones on the neckboard? I know that the arcing can't be good as it was causing some major issues with the picture and the blowing of the HOT.
« Last Edit: March 02, 2017, 11:39:11 pm by djsniperwolf »

ed12

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Re: Neotec nt2700n help
« Reply #18 on: March 03, 2017, 12:09:43 am »
the white socket on the neck board ?
if so that is a built in spark gap
i would double chk to make sure your neckboard is grounded to the metal dag of your picture tupe (metal dag =metal band that runs around the picture tube) and also to chassic ground as i remember the neo's
they ran 2 grounds

ed
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lilshawn

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Re: Neotec nt2700n help
« Reply #19 on: March 03, 2017, 11:31:18 am »
yes, i was going to suggest the same thing. possible ground issue on the neck.

  
 

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