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nem

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MS2930/31/33 chassis paired with a Toshiba A68KZN696X tube. This is the stock monitor in Blast City and Net City cabinets. Here's the gist:

Monitor develops a fault, chassis is removed, chassis is repaired, chassis is put back on tube, tube is dead.

Here's two posts from the last month and one more that's a few years older:

Sanwa 29E31S Chassis and Yoke on a Nanao MS2930 Tube
https://forum.arcadeotaku.com/viewtopic.php?p=511870#p511870
https://forum.arcadeotaku.com/viewtopic.php?p=463658#p463658

I've had a variation of this happen to myself as well. Here's my story:

I had a perfectly working, nice looking MS2933. I bought a replacement MS2931 chassis from Yaton. I thought I might as well test the thing. I connected the chassis to the tube, double checked everything, turned it on and saw a spark near the yoke, inside the tube. Turned it off instantly. Didn't think much of it, thought that the chassis is faulty. Connected the original working chassis back, turned it on, and surprise, no picture. There's some sparking in the neck. Connected the tube to a B+K CRT analyzer. Analyzer gives absolutely zero readings on the guns.
The end result in all four cases is the same. See the video in the first AO post.

@nnap has confirmed that high voltage arcing from a faulty chassis can fracture the tube rendering the tube useless. Please see his post (#7) below.

Something to keep in mind if you ever try untested chassis.

EDIT: edited the thread for updated info. I initially suspected it was the neck connector breaking loose. It's unlikely, but it hasn't been completely ruled out. Following replies refer to that.
 
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tiff_lee

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Is the 'seal' not actually fused glass?
 

Asure

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Its molten/fused glass. I've had one of these die in a similar way some years ago and believed the chassis shorts out something in the neck / rgb gun array. I guess this type of failure is common. Your left with a dead tube and don't know it. No hiss or pop. Replacement chassis will show a lightning storm around the neck/ purple inside the neck gun assy. Good luck finding a matching monitor for a blast :(
 

tiff_lee

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Well on the flip side I thought the problem with Blast's generally was a part on the chassis failing (flyback?) so in theory there should be many chassi'less tubes out there... although I dare say they all got binned
 

twistedsymphony

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I've heard of this happening to several other people as well.

I guess the next question is, what's the safest way to remove the neck board without damaging the tube?
 

nem

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Its molten/fused glass.
Here's a pic of a A68KZN696X tube neck:

ms2931_neck.jpg

If you're telling me the gray, rubber like substance that's between the plastic and the glass is completely inconsequential, then I'm probably mistaken in this matter.

For the record, the chassis that killed my tube, I actually tried it in another tube. The chassis went instantly to HV shutdown, however, the tube was fine.

Apart from the MS293X I have never heard of a chassis killing a tube.

EDIT: googling this, the gray glue is there to hold the black plastic piece in place, so I was indeed mistaken. However, if you search CRT and "gone to air", you get a lot of hits on vintage radio forums. The neck glowing blue is an indicator that the tube is "gassy", ie. there's air inside. Can a shorted tube produce the same result?
 
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nnap

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update on my tube. Tried another chassis/yoke combination on it, still dead. Got nice sparks in the neck though, so it really looked like there was no gas in the tube.

I decided to bin the tube and when I removed the yoke, it came right along with the neck of the tube. There was a fracture under the yoke. It was after the yoke mounting point towards the tube. I don't know if that was caused due to the high voltage arcs in the neck or something else. Anyway, there was not pop or hiss, so the gas was long gone before it snapped off completely.
 
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nem

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@nnap, thank you for confirming. So it is indeed high voltage arcing from a faulty chassis that breaks the tube and lets air in. Pretty unbelievable honestly.

Upside of this is that you don't have to worry about handling the neck I guess :/

I'll update the thread.
 

tiff_lee

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So it is indeed high voltage arcing from a faulty chassis that breaks the tube and lets air in.
So is the moral of the story here to service the chassis before they become faulty inducing an actual tube fracture/failure, in fact what kind of chassis failure would you need to cause the high voltage arcing?
 

nem

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Personally the moral of the story for me is that if I'm testing an unknown condition chassis, I'll test it on the worst tube I own.

But yes, it would be nice to know what kind of failure leads to high voltage arcing. When I have some spare time I'll look into the faulty chassis I have.
 

obcd

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Isn't the high voltage arcing in fact caused by the fact the tube isn't vacuum anymore?
Maybe the crt socket of some neckboards is having to much grip and you are damaging the glass at the pins when you remove the neckboard?

Obvious, if the neck is broken under the deflection coil, that's another issue. Maybe the neck becomes more fragile once the tube isn't vacuum anymore.
While it's vacuum, it has air pressing around it. When that situation changes, the glass will suffer different forces.

I hope our monitor specialist reads this and is able to give more accurate comments based upon his experiences.
 

RealMFnG

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So is it prudent to repair/maintenance the chassis without removing the neck? Or does it not matter?
 

kuze

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So is it prudent to repair/maintenance the chassis without removing the neck? Or does it not matter?
I would definitely still remove the neck if you are pulling the chassis out of the cab to work on it
 

RealMFnG

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Looks like pulling the neckboard is inevitable. Well, definitely taking it apart to clean the chassis, tube, and frame. Colors on MS-2933 seem really muted. Has some convergence issues I'll need to attend to as well. Holding off on recapping it until it is fully calibrated and reevaluate from there.
 

nnap

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hum, no I have to check my working MS-2931
 

cleure

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If you're telling me the gray, rubber like substance that's between the plastic and the glass is completely inconsequential, then I'm probably mistaken in this matter.
FYI, that stuff is just glue/epoxy, to hold the plastic "key" in place.
 

Hatsune Mike

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I have received a Blast tube that reportedly had a spark within the neck, and developed a fracture near where the yoke bonds to the neck.
 

Hatsune Mike

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From seeing it, I think it is much more likely that the crack caused the arc, rather than the reverse.
 
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