Ceronix 1793 Cuts Out after a few minutes

[Justin]

Could I... Just get a 1792 chassis and swap it onto my tube. Board is standard VGA. Seems like 1492 are easier to work with.

[rayydio]

good for you stud-boy... you stuck through it and fought it it the bitter end and kicked its ass!

[Chris-socal]

Do you mean a 1492 board? Unfortunately no. All the video is managed on the main board. Are you sure yours is standard VGA? Yours has two wires to the neck socket.
I don’t think 1492s are even VGA, I think they are the equivalent of CGA, standard resolution, whatever that is.

[Justin]

I was wondering about swapping the whole chassis. It does have two focus wires, but definitely is VGA. I pulled the quick swap connector from the monitor and wired it out a VGA breakout connected to a PC monitor and it showed the game. Obvious no touch screen so I couldn't do anything but proof of concept!

I bought a new flyback by the way. Could scratches in the insulated red patch on the tube cause any issues? I slipped with the screwdriver removing the anode cup a few times. Really sucks having it on the bottom.

[Justin]

It seems when it does the snap noise, it goes into shutdown then turns back on really quickly. Could the vertical deflection IC cause this? That's one of the other chips that had pretty questionable solder joints. I don't want to risk making them worse if they wouldn't cause the issue. Otherwise I would've reflowed them again already

[gametech2]

The snap is a very quick, short  burst of Hi Voltage leaking somewhere.
It can come from the anode cap on the CRT, taking the path of least resistance to the ground shield, or from a very small crack in the flyback transformer, arcing to the core (ground), or from the outer case of the flyback having a crack somewhere, and just discharging an "air strike" into the atmosphere if the air is humid enough. It also can come from the focus pot, or the g2 pot on the flyback if they are built in.
These are very hard to catch, you have to completely darken the area, stand clear, put a cover over the CRT, and watch carefully (or set up a video recorder) focused on the high voltage areas. Most times you can see where it is coming from.
 They used to make a substance that came in a small bottle, which was basically lacquer with some red dye in it, which we used way back in the day to cover the cracked areas and stop arcing.  Believe it or not, this was a pretty common symptom and cure with the older television sets back then.
 I can understand the monitor glitching, attempting a shutdown, and then resetting, because the high voltage either spiked, and/or dropped for a couple of milliseconds, then resumed normal operation. If you are not familiar with hi voltage in monitors, I WOULD NOT    recommend fooling around with that area much, you can get a lethal shock if you dont know what you are doing. 
just my 2cents.............................jb

[Justin]

I've always had a fear of CRT ever since I started working with them. It's been a few years now and I can actually bring myself to work on them (not shaking in fear removing the anode cup lol). I do not intend to mess with HV areas until I know it's discharged (I only tweak the G2 pot with power off). I'm sort of forced to work on it though as my wallet can't support getting it professionally repaired. CRT repair is very scarce and getting harder to find by the day.

I do however have a new flyback on the way! I'll swap that out and hopefully resolve the issue. I always thought HV arcing would be MUCH louder!

I have attached a picture of a CRT anode connection point (not mine because it is currently assembled in the machine). The red-ish coating is a little scratched up from my screwdriver. It's not a huge area scratched, but is this something to worry about? I heard of use of a grease to attach the anode cup that acts as a secondary insulator, should I use some of it, if so is it just dielectric grease or something else?

When I replace the Flyback, how of I adjust it properly. I do not have a high voltage probe to measure the EHT

[Chris-socal]

The product is called Corona Dope.
Justin, scratches in the red coating will not cause this. You can probably imagine how much is scratched off the tube I test boards on! Lol
Shutdown can be caused by the vertical IC but not HV pop.

This is most likely Flyback or any of the stuff jb mentioned. If you look really close at the FB you can usually see where it is leaking from. At first it might look like a hairline crack but when you look closely you might see a little pit forming where the HV is leaking out.

Corona dope can buy you a few minutes of time to help prove if you found the problem but modern flybacks have 25k or more and usually break through the dope. You could do something like wrap the flyback in really thick rubber tape and see if the arcing  reduces. Not a long term fix tho.

Stick with your plan and put a flyback in it. I still have those boards in my box.

Oh, I agree that your board is VGA but I don’t think a 1492 is. I think you could get away with another xx93 series but no guarantees. I have a 1493 and I think a 2093 board.

Chris

Chris

[Justin]

What would be the process for a person without special tools (me) to adjust the flyback properly? Also how would I attach the wires to the CRT socket?

[Chris-socal]

HV leakage varies in noise level. Don’t worry about the scratches.
You just described the reason most of us fix our own CRTs!
Wrap yours in black tape or something just to see if it blocks the arc.

[Justin]

I'll take a look after work to see if I can find a point of leakage. There is definitely carbon build up around the flyback so that could be an indicator.

[Chris-socal]

What would be the process for a person without special tools (me) to adjust the flyback properly? Also how would I attach the wires to the CRT socket?

There is a pin on one of the ICs, on a 1492 its pin 8 of LM324 and you set it for 4.6v. The manual usually says 50%…Thats because Ceronix boards do all of the bias control electronically. As long as you don’t have retrace lines, the IC will do the rest.
See attached, screenshot from 1793 manual! There is also a troubleshooting section in the manual on shutdown specific. For most of the tests you need a HV probe but it helps you understand that sometimes the internal coils on the FB fail and send the board into…..shutdown!

Imagine that!

[gametech2]

I never used the grease, I saw it on a few sets back then.
Ground the anode connection to the metal frame, and use a towel and some cleaner such as brake cleaner on a rag, and carefully wipe all around the red area, just enough to remove  any metal traces to the dark area (shield). Then go over it with a clean, dry rag, to remove any cleaner residue. be careful. CRT's are under a very strong vacuum. if broken, they can implode violently.
Unless you scratched it pretty deep, it isn't something to worry about.
the red stuff is basically what I was referring to that the factory used also to insulate the CRT anode.
while you are in there, inspect the anode lead going to the CRT very carefully. It may have a tiny crack in it.
............jb