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Arcade CRT - can just one gun go bad?

mathewbeall

mathewbeall

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Hi Folks,

I have a system here at work with a CRT I have been using for a few years - a 25". In the past week or so, the green output has just died on it - occasionally, and then comes back. One of the times that it had failed, I put in a different board, and the green was still out, so i concluded its not a board issue.

And it's also not a connectivity issues (I think) - since it just fixes itself for a bit of time. I have some male/female connectors that it plugs into (from the JAMMA wires) - that go up to the monitor input.

So - my question - can a particular gun (green in this case) just start to go "out" like this?

Matt
 
Yup, but there could be other reasons why it’s not working.
I would recommend buying/borrowing a CRT rejuvenator so you could test if the green gun has gone bad.
I have fixed plenty of tubes with my trusty B&K precision 467. Single guns included.
 
Perfectly possible for a single gun to go out, and as @BuddyC rightly says this is exactly the kind of fault that a CRT tester/rejuvenator is designed to test/find/fix. Also a humblebrag on the BK467 - it is god-tier and I want one badly. :)

Another common fault is for one of the colour transistors on the neckboard to go, there was an awesome video series where Randy Fromm covered quick fixes to return to service. Swapping the colour transistors around can help quickly test this common fault.

So my suggested course of action would be
1) shuffle the neckboard transistors and see if that helps
2) use a CRT tester/rejuvenator to test and hopefully restore
 
Cool thanks - probably a transister going is much more a likely culprit.

And like I said - it's completely intermittent - works fine for 90 minutes, then goes out for 20m, repeats in a random pattern.

Matt
 
Yup could be -

Neckboard socket / pins
Cold solder joints (in various places)
Transistors
Cabinet wiring/monitor wiring
Gun. Although a weak gun tends to go weak and stay weak. Or goes dead. There are lots of failure scenarios

You could save a lot of time with a rejuvenator. But if you dont have one in the meantime check the basics.
 
I am assuming the 3 transistors are the guys with the big heat sinks on them.

Edit - yep - P719 neckboard, Q503, Q504, Q505 - Sanyo 2Sc3782

What is the red stuff on the back of the board?
 

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Silicone that someone applied to protect trace repair. Looks like work has been done. Always should be a clue.
 
Oh yeah - I can see that now.... super obvious... well - I have a new small project... :)
 
what is the best way to get that silicone off so I can replace the transistors?
 
Probably alcohol and a plastic tool. Try the least intrusive first. Which would be scraping it off mechanically with a plastic screwdriver. Any remaining bits use a chemical etc.
 
I'd recommend starting simple.
Confirm that the video connector to the chassis/wireing harness is good I've had two monitors in the past exhibit this behavior and it was nothing more than a bad crimp or bad solder joint on the video connector.

Also check the adjustment pots... they can and do go bad and can also exhibit similar behavior.

going over the board looking for bad solder joints and just reflowing anything that looks even remotely suspect is arguably worth doing, maybe a cap kit while you're at it.

Guns can go bad but it's best to go over the chassis completely before looking at the tube.
 
I ended up buying some used neckboards from quarterarcade - that don't have a ton of trace repair work with silicon covering the wires. seems simpler to try and get going.

The picture is a bit dim as well though - we will see if the neckboard resolves that issue. If not - maybe someone in so-cal has a CRT rejuvenator I can rent... :)

Matt
 
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