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Another MS2931 struggle...

Posted: April 29th, 2021, 10:46 am
by Panther
I dealing with a MS2931 (With some black ooze on it). At first it was running some hours when I got the Blast City but then suddenly I had no picture anymore. Just heard two relay clicking, one by turning it on and another click few seconds after shut down, I suppose this is a kind of protection mechanism which kicks in...?

Anyway I was sending the chassis to a repair guy and he said he fixed it and it should work now. Well, it still don't and I hear the same clicking. So I thought it might be a issue with the yoke and I measured it. But I found different readings online, so I am not sure if my yoke is broken or if the tube is death, or whatever.

My readings are;

Original yoke

Red/Blue 1.7 mH and 0.5 Ohm
Grey/Brown 136.3 mH and 6.8 Ohm

Another yoke I bought reads

Red/Blue 2.5 mH and 0.7 Ohm
Yellow/Green 86.3 mH and 7.4 Ohm

Any ideas which yoke should work? Tube is a A68LBT696X
How can I check if my tube is death? Or should I look on the chassis again?

Thank you very much for any suggestions:)

Re: Another MS2931 struggle...

Posted: April 29th, 2021, 10:55 am
by nem
Faulty MS293X are known to take out the tube with them. That would be my first guess.


Ask your repair guy what the issue was with your chassis.

As for your yoke readings, neither of them make any sense. I measured mine and I got:

Lh 0.19 mH (red & blue)
Lv 15.1 mH (yellow & green)
Rh 0.5 ohm (red & blue)
Rv 6.8 ohm (yellow & green)

Re: Another MS2931 struggle...

Posted: May 1st, 2021, 6:24 pm
by Panther
I see, in my case I don't see any neckglow. My Ohm readings are the same as yours...Did I measured the mH correctly?
If my Yoke is really bad the tube might be still fine?

Re: Another MS2931 struggle...

Posted: May 2nd, 2021, 2:07 pm
by nem
Right, I meant your impedance readings.

Anyway, your yoke is fine based on the resistance. I think your tube might be toast, sorry.

Re: Another MS2931 struggle...

Posted: May 2nd, 2021, 4:19 pm
by Panther
But my mH are pretty different to yours? Are mH not important in this case? And if the chassis is good and the tube death, shouldn't be there any sparking in the neck when I fire it up? Sorry for my noob questions, it's my first time work on arcade monitor :oops:

Re: Another MS2931 struggle...

Posted: May 2nd, 2021, 5:01 pm
by nem
Sure, but your impedance readings are all over the place. Your resistance readings on the other hand are spot on. So I think your meter isn't really meant for reading yoke impedances.

As for the tube, easiest would be to connect another, known to be working chassis to it. Or connect your existing chassis to a different tube. Or ask around if someone locally has a rejuvenator you could borrow.

Re: Another MS2931 struggle...

Posted: May 2nd, 2021, 5:33 pm
by PrincessPrinPrin
Try the black lead in the hole with a - near the red one. And set it to 2mH for horizontal and 20mH for vertical.

Re: Another MS2931 struggle...

Posted: May 3rd, 2021, 11:14 am
by Panther
Okay, now it looks more or less closer to nem's readings, so this yoke should be good? :eh:
Lh 0.20 mH (red & blue)
Lv 16.08 mH (yellow & green)

I have another MS-8 and MS-9 chassis and a A68KJU96X tube (Which I don't want to bust) but no psu to test them.
Is it actually possible to use one those chassis to test the Blast City tube? (It's a A68LBT696X)
I guess the connectors are different and the voltages and yoke specifications as well?


Re: Another MS2931 struggle...

Posted: May 3rd, 2021, 1:00 pm
by nem
Well spotted by @PrincessPrinPrin.

The tubes are compatible, the yokes are not (0.200mH vs. 0.300mH for a MS9). However, they're not that far off that it should result in any damage, so AFAIK you could test the tube with a MS9. If you get any kind of pic, your tube is fine. This said, I've never actually done this.

Re: Another MS2931 struggle...

Posted: May 4th, 2021, 11:17 am
by Panther
Okay, I got my MS9 in hand now, so you say, I just can exchange those chassis for testing the tube and the yoke for a moment?
Can I just connect the power wire from the Blast City?

181585666_2935987596616591_6944816274484792127_n (1).jpg
Which of those two pins I should use for the horizontal wires, yellow or green?
And the power connector is the same as the one on the MS2931 (Blue circle), can I just plug it in? And whats the far right pin for? (Red circle)

Re: Another MS2931 struggle...

Posted: May 4th, 2021, 2:35 pm
by nem
Yellow circle is the horizontal yoke connector (red and blue).
Green circle is the connector for the degaussing coil.
Blue is for AC, your power input.
Red is a ground post.

Pictured below, purple is for the vertical yoke connector (yellow & grey).

yoke_connectors.jpg (80.81 KiB) Viewed 63 times