Nanao ms2931 help

[Maverick1978]

Hey folks. So as some of you may have seen, I've recently purchased a blast city (sega bass fishing) on the cheap for $300 locally.

I speak about it here: Blast city value?

Here's the monitor problem as told to me by previous owner: "He says he connected a 645 in 1 heros of the storm 2 and it wouldn't rez to the screen. He hooked it up to another 31khz monitor and it came on. S he thought it was a loose vga wire, so he tightened it and tried again. He heard a screech and the monitor shut off. From there on it flashes on briefly then shuts off again. Sometimes it stayed on but for the most part it doesn't, so he pulled the monitor to visually inspect but didn't see anything."

So the previous owner had the monitor pulled from the cabinet when I purchased it. I've been really careful to not touch the neck, to transport it carefully home, and it's sat untouched - until today.

I go to pull the chassis to mail out to pnl. I discharge the tube, then go to carefully pull the yoke board from the neck... When the whole neck tube moves. Wtf?? So I hold the neck in place, pull the yoke board, pull the chassis, and I try and see what I'm left with...

Ultimately, the neck is unbroken in and good visible shape. It sits nice and looks normal - until one lifts up on the back of the neck tube, where the entire thing raises as the "goo" that holds it to the crt tube are broken on left/right/bottom. Top portion is affixed still.

So... My question. Could this be the whole problem? And is it fixable - without sending it off?

I've a pic of the left of the neck tube as I'm lifting slightly.

 

[Mitsurugi-w]

If the glass tube the neckboard is attached to is moving then the tube is cracked and it cannot be fixed. All of the glass is one piece. Can't see anything in the pictures though.

 

[Maverick1978]

My apologies - I'm probably not using the right terminology here.

The glass tube the yoke board attaches to isn't moving.. There is nothing cracked or broken or moving at all on the neck tube.

However the entire neck tube is moving where it attaches to the crt.

I tried to get clear pix, but camera phone isn't the best. First pic is of the entire neck tube, trying to show nothing is broken on it.

Second pic is me lifting up slightly on the neck tube trying to show one of the 3 broken mounts where the neck tube as a whole affixes to the crt. Whatever that white epoxy stuff is that is used to hold the neck to the crt is broken through.

I guess I'm trying to figure out if my whole tube is toast, or if I can just apply new epoxy to hold the neck in place, then focus on my "broken" chassis?

Really out of my realm here. I can discharge a crt and recap a chassis all day long, but this is a whole other can of worms.

 

[Mitsurugi-w]

The neck is the glass tube that the neckboard plugs into. The part that slides over the neck with the coper wire wrapping is the yoke. A loose yoke won't prevent the monitor from working but a shorted one will. It's unlikely your yoke is shorted.

 

[Maverick1978]

Awesome... Thank you so much! Had me worried I had another problem and was going to be wasting my time with a chassis repair

I may have a line on a nanao 2934 monitor and chassis on the cheap from a Nascar arcade (same toshiba crt), but was really hoping not to have to spend anything else beyond my chassis repair. On all that, we shall see! That other monitor isn't going anywhere... Yet.

Thanks again

 

[XeD]

The white thing is like a silicone type adhesive that hold the wedges in place. The wedges are in place so the yoke does not move closer to the tube, which in turn will effect the purity of the colours. Does the yoke move if you gently push it with 1 finger? if so it is necked. A bad yoke will sometime give you a partial vertical collapse with a wavy picture. The only problem with a 2934 is you will loose cga (15khz) and ega (24khz) and in turn jamma games

 

[Maverick1978]

I haven't pushed in on it at all, so I don't know yet. Will try that tonight after work.

So far as the 2934, It appears to be the same tube, different chassis. If I went that route, I'd verify the 2934 chassis worked, then swap chassis with my 2931 and go from there.

 

[XeD]

If you do go the 2934 route I would check and make sure the yoke has a compatible reading for the 2931 chassis.

 

[nem]

Does the yoke move if you gently push it with 1 finger? if so it is necked.

Not sure what a loose yoke has to do with a broken neck?

This is the best CRT pic I found quickly googling:



The symmetry rings will sit where the twister coils are in your monitor. The PCB that connects to the top is the neck board.

So which part is moving again?

 

[Maverick1978]

@Xed: I've read about how a chassis has to be "tuned" to the display, but given that these are the same model displays, I would have thought that any "tuning" would be pretty close. Any guides/further reading you could point me to on these readings you mention, and how to tell if the yoke readings are correct for the tube? - bear in mind that my current 2931 doesn't work, so I can't exactly take comparison readings from it, assuming that would be normal procedure.

@nem: Apologies - my terminology is wrong. I'm still learning this stuff.

What I referred to as the "neck tube" is essentially the entire "funnel" that attaches to the CRT display itself.

Where it's broken is where that piece attaches at the CRT. And when I say broken, I mean that the silicon adhesive that holds the thing in place has dried and cracked and now allows some movement. The wedges that XeD mentions appear to still be held in firm place.

Using your pic, I've circled where these glue-mounts would be. Well, kinda There's 4 of them: top, bottom, left, right. B/L/R have given way and there is some movement away from the CRT itself. It's unknown if there is forward movement into the CRT display that would, as XeD suggests, cause color impurity.

 

[nem]

@Xed: I've read about how a chassis has to be "tuned" to the display, but given that these are the same model displays, I would have thought that any "tuning" would be pretty close. Any guides/further reading you could point me to on these readings you mention, and how to tell if the yoke readings are correct for the tube? - bear in mind that my current 2931 doesn't work, so I can't exactly take comparison readings from it, assuming that would be normal procedure.

Well, you need to measure the yoke that you currently have and then find out the specs for the yoke on the 2934. You don't need the 2931 chassis for this part.

What I referred to as the "neck tube" is essentially the entire "funnel" that attaches to the CRT display itself.

That's the deflection yoke or yoke assembly as it is in the picture.

Where it's broken is where that piece attaches at the CRT. And when I say broken, I mean that the silicon adhesive that holds the thing in place has dried and cracked and now allows some movement. The wedges that XeD mentions appear to still be held in firm place.

Using your pic, I've circled where these glue-mounts would be. Well, kinda There's 4 of them: top, bottom, left, right. B/L/R have given way and there is some movement away from the CRT itself. It's unknown if there is forward movement into the CRT display that would, as XeD suggests, cause color impurity.

Well, it's not broken in any way. It's pretty common that they're loose. Like you said, the adhesive dries and no longer holds the yoke in place. However, there will be no forward movement because the clamp is it keeping in place. It's just small lateral movement.

 

[twistedsymphony]

You need a serious CRT anatomy lesson...

The "Tube" is the glass part of the CRT.. ALL OF IT. And it extends from the part you look at in the front all the back to, and INCLUDING, the plastic circular connector that the "neck board" plugs into.

here's a good picture of a mostly naked Tube:

This is NOT 2-parts, it's one giant piece of glass.

What you normally see wrapped around the back of the tube is a funnel shaped electro magnet called a "yoke", when removed from the CRT it looks like this:

The yoke attaches to the tube with one, sometimes two circular clamps that squeeze the neck of the tube (you can see this in the picture above: the metal ring with the bolt to tighten it is the clamp). At the front there are little rubber wedges that serve to both hold this in place and help align it properly with the the tube.

The yoke is what directs the electron beam to the appropriate part of the screen, without it you'd get nothing but a little white dot in the center. When the yoke is mis-aligned you will get "convergence" problems which is the red/green/and blue colors separating on screen like this (this picture SHOULD be a white grid on a black background, if the convergence was adjusted properly):


Convergence is adjusted by physically shifting the position of the yoke, and by moving the black rings you see on the yoke above. Adjusting the Convergence is an ENORMOUS pain in the ass, so that's why these things get glued down with that white silicone glue you see, so it doesn't shift around.

The yoke has a 4 pin-connector... red and blue are generally for the horizontal windings on the yoke, and the yellow and brown are generally for the vertical windings on the yoke. Fun fact if you swap the red and blue pins it will produce a picture on the CRT that looks mirrored. (may older games that used a mirror in the cab actually had these pins swapped so that the resultant image would look normal)

I assume you know that the "Chassis" is the circuit board that controls the monitor, generally the "neck board" and the "remote board" (the small external board with the adjustments on it) are also considered part of the chassis.

To check compatibility of the yoke with a different chassis you will need to measure the resistance of both the vertical and horizontal pin sets to make sure they're within the spec that your new chassis expects. This is also how you can determine if your yoke is bad, as it will either show 0 resistance, and open circuit, or be out of spec. What's "in spec" or "out of spec" for a yoke? That changes quite a bit from monitor to monitor so you'll need to do some googling and figure out what it should be for the original chassis and what the new chassis needs.

A lot of people suggest swapping the yoke when swapping the chassis, but there are debates on whether or not this is really necessary or prudent.

-----------------
The rest of it....
the heavy wrapped wire that goes around the parameter of the tube, usually plugs into the chassis with a 2-pin connector is the degauss-coil. This helps de-magnitize the tube. without it you'd end up getting rain bow patterns in the picture usually in the corners. This is what makes the buzzing and the slight wiggle to the image when you first turn it on. The chassis has a relay that runs AC power to this coil for a few seconds when powering on.

the degauss coil can stay with the tube though you may need to swap to a more appropriate connector.

The metal brackets on the 4 corners of the tube are called "ears" or "mounting ears", and the structural metal bits that hold the chassis and the tube together is known as the "Frame", and not all monitors have this. in a lot of cabs the tube and the chassis are mounted directly to the cabinet itself.

You will also notice some bare metal wires running along the outside of the tube and a gray powdery sometimes greasy coating on the back of the tube (called "Aquadag")... these are important, vital parts of the tube used to ground it properly... DO NOT attempt to wipe off or clean this material off of the tube.

------------------------------
Basic Trouble Shooting:
Yokes don't typically go bad, I mean it's just a bunch of wrapped wires. so a bad yoke usually suffered some physical damage causing a short or a break in the windings somewhere.
When that happens it usually causes some other component on the chassis to burn out as a result. So it's important to check the resistance even if you've sent the chassis out.

if you do happen to just get a single white dot on your screen, it's not usually a bad yoke, but rather the circuit on the chassis that controls the yoke has failed. Similarly when convergence issues first start cropping up it could be due to bad/weakening caps on the chassis. The signals being sent to the tube and yoke are weak or sloppy and as a result you start to get bleeding and blurryness in the picture. Replacing the caps generally resolves this and could save you from having to do a convergence adjustment. Similarly if you do a convergence and then replace the caps, you may have to do it AGAIN... so yeah, caps first.

If you are getting a single line or just a dot, usually it's the fault of the "Horiztonal Output Transistor" or "HOT" this is the device that converts the incoming sync signal into pulses used to control the yoke and drive the position of the electron beam. if the HOT dies your image "collapses". Other components can sometimes cause this behavior as well. and sometimes other bad components can kill the HOT, or prevent it from functioning. Unlike Caps the HOT either works or it doesn't. so there's no need to replace it unless it's not functioning at all.

When powering on if you're not getting a picture you should also check the neck of the tube for a yellow/orange glow (like an old, weak light bulb) This means that your tube is receiving power and it's a good sign. If you're not getting any glow, then it means something is wrong with the high voltage circuit, which could be anything from a blow fuse, a bad flyback, a cracked tube, or a number of other chassis problem.

 

[Maverick1978]

** edit... Scratch all this. Tube is necked. The yoke isn't what is moving. The tube is. It doesn't really move when I gently press one finger in however I can hear a slight grinding sound. With crt face down on a moving blanket and gently lifting the ring on the yoke, the end of the tube with the pins moves - not the yoke. More slight grinding noises. I took a really poor video with my phone... I'll have to see if I can get it shared sometime tonight to gather you guys' opinions. You're certainly alot more informed than me.

----
Thanks for the anatomy lesson - seriously. I sincerely appreciate the level of detail there (and being a detail-oriented guy that some would call long winded, I love posts like that!)

Some of the info I knew (chassis, caps first, degauss coil), some of it I obviously didn't. Here's the trick... when I mentioned that I "lifted up slightly" on the "neck tube," I was lifting up on the pin-end of the tube. And it was moving the yoke slightly. (see pic in case I'm screwing up terminology again!)

I'm suspecting that this is bad, and that my monitor is necked. And if it's necked, then it's been that way since I purchased it non-working with a chassis problem, and I didn't know enough to check it.

I have never applied power to the monitor. At this point, I've pulled the chassis, but it's easy enough to install again.

So, at this point, I'm suspecting that I need to do the following:

1. check resistance on the yoke, if 0, yoke is toast. If not zero, it's good... though not necessarily in spec. Move on.
2. reinstall chassis (since I haven't sent it out yet), power on monitor. Check for glow in the tube in front of pins. If glow, good, if no glow... more work.
3. Assuming glow, pull chassis and mail it off for repair, just in case.

Given the information above regarding the lift in the neck, would it be prudent to pull the yoke, despite the convergence issues that it will cause, to ensure that it's not necked?

As an aside... I'm beginning to realize why the monitor was pulled from the cabinet when I purchased it. The better to not apply power and check in more detail for things (tube glow is one of the first checks I do when messing with my vintage computer monitors when a screen doesn't light up immediately). Sigh... live and learn.

 

[zero238]

Might need to put the anatomy lesson as its own thread. I can also help to put the different boards and stuff that makes it run.

 

[twistedsymphony]

The inside of the tube is a vacuum so if the glass is cracked the then air rushes in and contaminates everything inside and it's toast... just like when air gets inside a lightbulb the oxygen and other particles against the metal bits cause them to burn up. A "necked tube" is about as valuable as a burnt out light bulb.

the connector on the end of the tube shouldn't have any play, though I don't think it's impossible for it to have a little bit of movement and still be ok. if you push gently on the glass part just next to the connector does it move and does the yoke move with it? if so then I'd say it's definitely necked.

I don't now what benefit there is to hooking up the chassis. If you hook up the chassis and power it on and the neck is indeed cracked then you'll likely hear high voltage arcing across the crack in the tube. I honestly don't know if or what kind of damage it could inflict on the chassis, but chances are that damage is already done anyway.

-----

In most arcade machines your option is to find another similarly sized monitor that supports the same resolutions but unfortunately with candy cabs like the Blast the shape of the cabinet is designed to fit around specifically shaped tubes. the most common 27" Tri-sync in the USA is the Well's Gardner D9200 and by all accounts it doesn't fit right in a Blast. requires special mounting and even then leaves gaps.

I've seen some success with people mounting in 27" tubes from Sony Trinitron TVs and the chassis on those can be modified to accept an RGB signal.. but it's A LOT OF WORK and the results are still less what you'd get from the original monitor.

 

[Maverick1978]

If I push gently on the glass part in front of the pins, the whole piece moves, yoke and all, like it would if it's broken nearest to the back of the display tube like I suspect.

I may very well have access to the exact tube that's in my blast. That tube is in a Nascar racing cab that's a parts machine, and has the ms-2934 31khz chassis attached to it. From what I've read, that chassis and the 2931 chassis are usable with these tubes, though I don't know about whether the yoke on the Nascar tube is the same. I suppose it would be possible to swap the yoke and chassis on the Nascar tube with the one on mine. More research needed here....

And I kinda need to get that 2934 monitor first. It's a parts machine that my landlord owns for another one that was working up until recently.

Obviously the d9200 is another choice, but man, I really wanted that tri sync working if I can get it...

 

[twistedsymphony]

definitely see if you can get the monitor out of that NASCAR machine.

 

[XeD]

I figure it would be necked as nothing should really just removing the backboard. One of my 9blast city did the same thing. All I heard was acring when I turn it on. I guess it broke during transport? Any way good luck with finding a replacement. If these thing weren't so delicate and heavy to transport, I would send my spare from a 2933

PS: great write up @twistedsymphony

 

[Maverick1978]

I appreciate the thought, XeD.

I've a feeling that I'll be ok, one way or the other. Landlord has 2 Nascar cabinets. He got them for free along with a trailer full of like 15 other cabs and a few pins. Never mentioned it to me, laugh, just sold them all to a dealer that fixes the easy fixes and sells as collectibles, then guts the rest for 1000-in-ones, no matter how collectible the cab. I think he got $100 per on the cabs, 400 on a star wars pin, and 50 ea on the slots. As one Nascar is parts only, and the other recently stopped working, I'm hoping he will give me a similar deal. I wouldnt mind having two nanao 2934's around.

We will see.. Hopefully he will make up his mind soon. I'm hoping to not have an empty Blast around for a year or two!

 

[nem]

The tube from a 2934 will definitely fit a Blast. I've never measured the yokes, so I can't say if they're the same.

You should jump on that 2934.

PS: great write up @twistedsymphony

Agreed. Needs to be put in its own thread.