Got a brand new K7400. Weeks later and I have a black dot on the screen. Help! (PIC)

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Got a brand new K7400. Weeks later and I have a black dot on the screen. Help! (PIC)

Hello! After searching for literal years, I finally found a K7400 brand new in the box. I paid $380 for it and I was happy to shell that out since it seems like it's not much more than used ones go for. Anyway, I got it and it in fact was brand new. Who keeps them in a box sealed for a decade? I do not know but I am glad they did.

Anyway it has been working perfectly but completely out of nowhere a black dot appeared on my screen. It's small, but it is annoying. I am sure anyone who ever had a PSP or DSi or new flat screen TV with a dead/stuck pixel can feel my pain.

I do understand that CRTs do not use pixels so what I am saying might not make sense, but I am describing what it looks like. Trying to figure out what it is has gotten me nowhere, unfortunately; making me realize my problem is probably incredibly unique.

Here is a picture, close up, as it runs the title screen to TMNT The Arcade Game:

iM5a2U7.jpg


That was the best close up pic I could get without the camera going blurry or going crazy from the refresh rate differences. I hope it is helpful.

Some things of note:
  • -This was not here when I got the monitor. It just came up out of nowhere.
  • -I bought a degaussing coil to see if it would "move" it. I also adjusted the screen size and height and width and all that and the dot does not move with it.
  • -I have lightly tapped the monitor to see if it would move, in case it were just some sort of debris (not that I could see any way debris could ever get IN the glass!) and it did not move.
  • -I can still see it when the monitor is powered completely off.

I know this is an odd one, but any help would really be appreciated. I am extremely OCD (not hyperbole) with this stuff which is why I specifically wanted a brand new monitor; just because even the lightest scratch or burn in drives me crazy (I can't help it, I wish I could) and for this to pop up on a brand new monitor is pretty disheartening. I can kind of ignore it if playing something like MK2 or Killer Instinct but it's really annoying with pretty much any other game that doesn't have "busy" graphics.

Any pointers or even ideas as to what it could be and any advice on if it is possible to rectify, I would greatly appreciate it. Thank you!
 
Yeah, if adjusting the screen has no effect on the dot's location, I would agree it is the tube.

Sorry.
 
you may have to do a tube swap if you can find one because it sure sounds and looks like a problem with the phosphor/tube defect.
 
Geez, a tube defect? I just bought it recently. Does this type of thing just get worse? How does it manage to get this blemish anyway? Again it was not there when I got it, which is really confusing.
 
I had a very similar issue with a brand new 7400, there seemed to be an issue with the yoke in mine. I ended up swapping yokes and the issue went away, but here's an image for reference.

r3GDgCdl.jpg
 
I had a very similar issue with a brand new 7400, there seemed to be an issue with the yoke in mine. I ended up swapping yokes and the issue went away, but here's an image for reference.

r3GDgCdl.jpg

Wow, that whole bottom right part was all black like that? Did you see it even when the monitor did not have power?

Also you didn't happen to buy it from a guy in South Carolina, did you?
 
Not at all, and if I twisted the yoke with the power on, it would move across the screen. I did not see any blockage or defects in the copper windings, I have no idea what causes this. It was a simple enough fix that I did not put much thought into it.
 
The only reason I posted, is because perhaps your issue is similar but in a much smaller scale.
 
I had a very similar issue with a brand new 7400, there seemed to be an issue with the yoke in mine. I ended up swapping yokes and the issue went away, but here's an image for reference.

r3GDgCdl.jpg

Did a degaussing coil have any effect on the location of the black spot?
 
Not at all, and if I twisted the yoke with the power on, it would move across the screen. I did not see any blockage or defects in the copper windings, I have no idea what causes this. It was a simple enough fix that I did not put much thought into it.

Wow, it does sound like my issue possibly! Were you able to see it while the power was off, though? That's what's confusing me so much. I will try to move the yoke a bit.

Odd indeed.

I guess OP can tap/twist on the yoke to see if that moves it a little.

And than try to find a replacement K7400 yoke.

Thanks so much. From your experience, this screen blemish would be noticeable even with the screen off, correct?
 
Thanks so much. From your experience, this screen blemish would be noticeable even with the screen off, correct?

Nope, I wouldn't think so.

If I follow, the description here is that the yoke has a "blind spot" that just doesn't work. Hence you have to wiggle the yoke to move the "defect" on the screen.

That said, your "defect" at this time is really small. Read up on converging yokes before you decide you want to go down the yoke swap road. You could end up a LOT less happy with the results.
 
^ is following along. The blind spot was only seen when the tube had an image. It looked perfect when it was not powered on!
 
OK so it is not the yoke since I see it when the screen is off. Is it even humanly possible for a mosquito or some other odd debris to get over there?
 
"over there" as in "inside the tube" no... take a picture to show the whole tube when off, and one when it's on. It sounds like you have a defective tube, no worries though, pretty common glass to find around still...but who knows for how much longer.
 
"over there" as in "inside the tube" no... take a picture to show the whole tube when off, and one when it's on. It sounds like you have a defective tube, no worries though, pretty common glass to find around still...but who knows for how much longer.

OK, I am having difficulty getting a good picture of it. I will keep trying. But basically when the screen is off, the dot is a bit darker than the rest of the monitor, so that is how I can tell it's there even with no power.

As for the tube being defective...isn't the tube just the glass? I am a bit confused how the tube could be defective. But I am glad that means it might be a (hopefully) cheap fix. Are you saying I should just try swapping out the glass? Sorry; I did a bit of searching for which part specifically is considered the tube and I am not really seeing specifics. Everyone seems to call the entire monitor the tube.

Could this have come about from the way I am powering down the machine? I simply have it hooked up to a UPS battery backup, and I just flick the switch off when I am done. Remember that the k7400 does not require an iso transformer. I am not sure if something I did could have caused this.

edit: is it possible one of those things people hook up to the yoke that "blast" the guns would fix this? Someone in my area was telling me about them; it hooks up where the neckboard is and will fix color issues and stuff like that. I doubt it but was wondering if I got one of those if it would fix it.
 
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