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Those chassis are use and scrap, on the main there is little board placed vertically it should control the hv but if something go wrong in this little bastard, the Cassis just kill the the tube in one sec , releasing itself in "overload protection" Or in the worst case just ready to destroy another next tube!!!
You will never be able to repair this little board and also you should not risk to destroy another tube!
The board uses an IC that can be acquired NOS from a few vendors, and aside from two capacitors this board is not too fragile.
 
The board uses an IC that can be acquired NOS from a few vendors, and aside from two capacitors this board is not too fragile.
Unluckely the ic (MPC..) is not the issue you can easily replace this and the chassis will remain in protection or ready to destroy another tube, most likely any other smd fuse resistor or t.. Still not find out a solution but slso not want spent any other minutes on this chassis.. As far as I know the only one I know who repair or still try to repair those chassis is located in Spain and he is very good at repair maybe he can find a solution.
 
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The thought of this terrifies the heck out of me since these tubes are so hard to come by and these chassis are known to be a pain to work with.

Considering selling my blast and getting an Astro instead. Or maybe just wait for Axun to open up the preorders again for a supergun set up in the end lol.
 
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The thought of this terrifies the heck out of my since these tubes are so hard to come by and these chassis are known to be a pain to work with.

Considering selling my blast and getting an Astro instead. Or maybe just wait for Axun to open up the preorders again for a supergun set up in the end lol.

Actually, I find suitable TV donor tubes that are a fitment replacement match for MS293x monitors quite readily, at least in the US. For every 27" curved donor I pick up, 4-of-10 will work for the MS293x. The rest get recycled. Maybe it is different in AU?

Donor TV tubes for MS8/9 monitors are impossible to find. As of yet, I've only found MS8/9 donor tubes can only be sac'ed from other arcade brand monitors like Kortek.
 
Don't give up @klee123 -- you're not going to find an Astro easier locally and the Blast is a nice machine when up and running.

I'd give Joey (Jomac) a call and genuinely explain to him all that's going on. He's a top bloke and can probably help out or give solid advice. You can just drop him an e-mail to the address on his website if you don't wanna call.

He's helped me out in the direst of situations in the past.
 
Don't give up @klee123 -- you're not going to find an Astro easier locally and the Blast is a nice machine when up and running.

I'd give Joey (Jomac) a call and genuinely explain to him all that's going on. He's a top bloke and can probably help out or give solid advice. You can just drop him an e-mail to the address on his website if you don't wanna call.

He's helped me out in the direst of situations in the past.
Joey, is the only one who can doing something, he is the best technician for monitor chassis all over the world, he just no more service any chassis outside the Australia but I hope he will do an exception!
 
Yep, we’re extremely lucky to have him. Not only talented but a great and genuine person too.
 
Yep, we’re extremely lucky to have him. Not only talented but a great and genuine person too.
15 Years ago I talked with him, I was from Italy, was just an honour for me! Great person and a precious resource!
 
Actually, I find suitable TV donor tubes that are a fitment replacement match for MS293x monitors quite readily, at least in the US. For every 27" curved donor I pick up, 4-of-10 will work for the MS293x. The rest get recycled. Maybe it is different in AU?

Donor TV tubes for MS8/9 monitors are impossible to find. As of yet, I've only found MS8/9 donor tubes can only be sac'ed from other arcade brand monitors like Kortek.
I'd say availablity would be the likely reason, however from what I've read the Astro MS9 Monitors/Chassis are generally more reliable? At least people I know who service Arcade monitor chassis are willing to service those over the MS293X.


Don't give up @klee123 -- you're not going to find an Astro easier locally and the Blast is a nice machine when up and running.

I'd give Joey (Jomac) a call and genuinely explain to him all that's going on. He's a top bloke and can probably help out or give solid advice. You can just drop him an e-mail to the address on his website if you don't wanna call.

He's helped me out in the direst of situations in the past.

Well, I'm going to give neckboard on the replacement 2930 a test, so definitely not giving up :thumbup: . Thankfully the replacement chassis is working(and god is the replacement tube is so nice), just need to sort out the missing blue color.
 
I'm the latest victim of this. Ms2931 Chassis bench tested by PNL for 8 hours. Worked for a few minutes and then a loud screech. After some troubleshooting I suspected my tube was shot. Confirmed with my rejuvenator that it was dead. Salvage the yoke and found this bad boy. Fun fun
 

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Dumb question for the CRT experts. If I test the 2931 chassis on a 25" tube, will i just get a really crappy image or could i potentially damage the chassis? The tube is a throwaway tube on it's last legs with really bad burn in, so I would not care if it broke the tube. I would care if the chassis took damage however....

I just want to test the chassis on something without risking another hard to find semi flat 27" tube....
 
The test CRT will need similar specs on the deflection yoke. Also, by using a chassis designed for a larger tube, you might be overdriving the High Voltage. This bit is potentially dangerous since you start to generate X-Rays when the HV gets too high or trigger the chassis X-Ray protection circuit (assuming it has one). Its not a huge difference in tube size so you might just need to turn the HV down a bit if you can find a test CRT with similar DY specs.
 
It is possible for a chassis to break the tube. The line output transistor (horizontal output transistor depending where you live) not only drives the scan left-to-right deflection, it also via the Line output transformer (LOPT, horizontal output transformer) derives the EHT voltage for the tube.

The waveform on the transistor requires tuning, so you'll find 1 or 2 capacitors across it, generally around 8200 pf or thereabouts. If the capacitor falls off or goes open-circuit, the transistor will pass high-voltage narrow peaks through the LOPT, resulting in the EHT rising to crazy values. This can cause a spark to jump from the internal coating, through the glass to the scan coils (yoke), puncturing the glass and admitting the air. The hole itself will usually be star-shaped, but a particularly violent activity could cause an implosion of the tube.

The EHT spark that hit the yoke can then run amok, blowing up ICs and other parts all over the place - something like getting hit by lightning.

As you can imagine, the time taken to track down and replace all the broken bits can cost a lot of money to repair. Then the new tube needs alignment of the yoke and magnets for purity, which takes even more time.

The last generation of CRT TV sets had protection against just this sort of thing happening, shutting down if a fault was detected and hopefully saving your precious tube.

Of course, faulty badly-made tubes do exist and the neck is the most likely place to break.
 
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In the event the chassis malfunctioned and caused the spark that cracked the glass, will I see obviously damaged/burned components on the chassis?

Or could the chassis itself be OK after an event like this?
 
Depends what you mean by obvious. A cursory glance probably won't reveal anything, but it's unlikely the chassis will survive intact.

If you turn it on, look for one of these: heater in the tube not lighting up; sparks in the tube neck; arcing around the yoke; the spark gaps on the neck lighting up.
Of course if you do see sparking, then other parts are probably breaking as you watch.

Another thing you could do is to loosen the yoke and carefully slide it back, then look for the hole where the yoke was (could be underneath).

Those tuning capacitor(s) are very important !! You must make sure they are soldered properly and not bulging or burnt.
 
Depends what you mean by obvious. A cursory glance probably won't reveal anything, but it's unlikely the chassis will survive intact.

If you turn it on, look for one of these: heater in the tube not lighting up; sparks in the tube neck; arcing around the yoke; the spark gaps on the neck lighting up.
Of course if you do see sparking, then other parts are probably breaking as you watch.

Another thing you could do is to loosen the yoke and carefully slide it back, then look for the hole where the yoke was (could be underneath).

Those tuning capacitor(s) are very important !! You must make sure they are soldered properly and not bulging or burnt.
It already broke the tube. But the chassis looks fine, it even still turns on. I turned it on many times before I realized the tube was cracked.
 
On the 293X series the horizontal circuit is completely isolated from HV. You can even remove the HV fuse and run the chassis sans HV. Robbbert's notes and advice are sound and applicable for more typical fixed-scan chassis (televisions, MS9, MS8, wells-gardners, etc).
 
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I would like to remind everyone that getting a replacement tube for a MS2930 is a huge PITA. Best guess right now that for this chassis the problem is the two SMD caps on the MSPAC004 sub-board:

mspac004_1.jpg


Left cap is 2.2uF 50V, right cap is 22uF 6.3V. Both caps are 4mm.

I actually measured the old 22uF cap on the chassis that blew my tube and at least the ESR is way off:

mspac004_2.jpg


Here's a brand new 22uF that I measured just now for comparison:

mspac004_3.jpg


The 2.2uF cap seemed to be in spec.

If you've had your MS2930 "serviced", more than likely they haven't done jack shit to the SMD caps. Get them replaced!

Thanks to mufunyo on Arcade-Otaku for the tip.
 
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Strange. I have like 2-4 suitable MS2930 tubes handy. MS9 tubes are another story.
 
I'm the latest victim of this. Ms2931 Chassis bench tested by PNL for 8 hours. Worked for a few minutes and then a loud screech. After some troubleshooting I suspected my tube was shot. Confirmed with my rejuvenator that it was dead. Salvage the yoke and found this bad boy. Fun fun
nice shot of the "exit wound". I can't help but notice that that pinhole is right below the enormous resistor that goes from the anode/HV to pin 4 on the neck. This further supports my theory that an arc is happening through the neck to the yoke. Perhaps this is something that happens as a result of a spike in HV.
 
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