Nothing, hopefully, is shocking.

May 3, 2009 2:24 PM

Yet another "how do I overcome the fear of touching this CRT" question, this time somewhat specific to Atari vector monitors.

So, I picked up an old, used Tempest machine. The cabinet's in decent condition, I rebuilt the spinners, and the monitor's bright with no burn-in. It plays great, and I'm pretty happy.

There's one small issue, though, and that's a hint of instability in the video. The display is just slightly unstable -- not enough to affect gameplay, and not enough that you'd even notice the slight jumpiness from a couple of feet away, but it's still there. I'd love to get it rock-solid, and from my reading, it sounds like a cap kit and some resistors on the HV board and a new LV board might do the trick. I went ahead and ordered those parts and have them in my possession.

The problem? While I've worked quite a bit on pinball machines and PCs, and feel comfortable will all of the other parts of the Tempest, I've never done CRT repair, and I'm well familiar with the danger inherent in repairing old monitors. I've read the online repair docs, have watched the videos of people doing the discharge, and I still don't have the 100% confidence the repair guides recommend.

My two questions:

1) Is a certain, slight amount of instability correctable in a Tempest, or will there always be just a little bit of jumpiness? I hadn't seen an original Tempest machine in years before picking this one up.

2) How can I get to 100% confidence to work on this kind of monitor? I live in the Bay Area, and would consider paying an experienced hobbyist to go through the removal and discharge procedure with me a couple of times so I can get up to speed, but I'm not sure that's an option. How did you get confident working with CRTs on your own?

posted by eschatfische to computers & internet (8 comments total)

Personally I'd never be 100% confident about CRT work on principle - and I might be misinterpreting, but I'd never do work on a tube literally on my own - make sure there's always someone within earshot (ideally in the room, and ideally trained in CPR.)

Fwiw, I was trained by someone who'd been repairing TVs for decades, and it was extremely reassuring to have someone standing there who could confirm that I'd discharged it correctly the first time I tried - and who was willing to poke the EHT terminals to prove it. I don't know how comprehensive the internet videos and documentation is, but the working practices are also important; make sure that you discharge the tube every time before you go near the terminals (especially after they're disconnected), watch out for charged HV caps, never reach into the live chassis, be slow and methodical when working, etc. For a long time I literally sat on my left hand whenever possible when working on a live set.
posted by Luddite at 2:56 PM on May 3

Luddite and I must have known the same people. I am not sure where I picked it up, but when I've had to discharge something, I would always end up in this strange pose: left hand either behind my back or in my pocket, left leg tucked up behind me. Looks dorky as hell, but I always feel safer doing it.

I think perhaps a little bit of non-confidence might serve you well in this case. 100% confidence can quickly lead to casual behavior.
posted by adipocere at 6:35 PM on May 3

Discharging the HV on the CRT is no big deal. It's scary but over really fast. In fact, usually you don't even hear it. I use a looooong, thin flathead screwdriver and a beefy jumper clip with one end on the screwdriver blade and the other on the chassis. Not familiar with this particluar beast.

It's such an arcane thing to do these days, I'd heartily suggest finding a ham radio operator in the 55-75 year old range and get him to help. Barring that, a middle aged electrical engineer and barring that, a retired TV repairman.

Honestly, the high voltage is less likely to kill you than the supplies in the 500 volt range, which have substantial current capabilities. Mains voltages are much more likely to nail you than charges built up on tiny caps in a TV. Not to say they won't, but rest assured, if you do this 100 times, you'll get nailed several times. You either get careless, overconfident, make a mistake, or fail to be prudent. Unplug the set. Two or three times. Don't work alone on lethal voltages.

I am not sure why you think you need to make alterations to the HV and/or LV power supplies.

'Instability' in a video display can come from several things. Usually, there are horizontal and vertical hold controls and I'd go for basic adjustments before going any deeper. Noise on a low voltage power supply MIGHT impact stability, due to its potential effect on the sync circuits, and I'd have to see the symptom to assess the likely cause.

There are almost too many variations to type, but if you'll take some pix, label the areas where the effect is seen, and post a link, I'll peek at it and see if I can shed light on what you are seeing.

Is there anything else you can describe about the symptom? Is it content-specific (i.e., more noticable when the screen is displaying bright or dim scenes)? Is it thermally sensitive (i.e., goes away/comes back when warmed up?). Are you close to any sources of magnetic energy (big ass speakers, motors, etc?). What year was this thing made?
posted by FauxScot at 6:37 PM on May 3

I used to work in a computer store where I worked on lots and lots of first generation iMacs with CRT's in them. I must have discharged dozens, and never got used to it. It does help to have someone around to show you the ropes the first few times, but the bottom line is: there will always be (or perhaps, should always be) a healthy amount of fear associated with not only the discharging itself, but actually disconnecting the tube from power.

As for your first question, I don't have any experience with Tempest machines in particular so I don't know. I can tell you that it's not uncommon for CRT's for get a bit of judder. You may be able to adjust the CRT focus without having to do the discharge and see if that helps before you replace the HV and LV boards. I used to have a set of plastic tools specifically for this; I'm not sure if the adjustment screws even exist on your CRT.

Don't get fried, and good luck!
posted by littlerobothead at 8:04 PM on May 3

Given that the consensus is that I really should have someone to show me the ropes (or at least "spot" me while I do it), short of Fauxscot's recommendation that I find an older ham operator, any other ideas on how can I find a person who I can hire / cajole into spending a few hours with me and my machine to learn how to do this?

Fauxscot, certain HV power supply components are known to cause instability when they age on the Tempest monitors (according to the Atari Vector repair FAQ). Various Atari repair sites also recommend rebuilding the low-voltage board if you're going to be opening the thing up because it's especially prone to failure. A still image wouldn't be helpful for diagnosis, the instability results in a small amount of "twitchiness" that isn't captured in a still image.
posted by eschatfische at 9:29 PM on May 3

If you don't think you can find anyone just by asking around, post a note on Craigslist.
posted by mikepop at 5:46 AM on May 4

go search the rec.games.video.arcade.collecting newsgroup. That bunch of guys has many years experience doing the type of repairs you're talking about, and they're willing to answer questions. groups.google.com and search for rec.games.video.arcade.collecting. There's probably somebody on that group near you who'd be willing to help.
posted by cosmicbandito at 3:43 PM on May 4

Give T-Minus One in Benicia a call. They do arcade game repair and fixed my cocktail of this very same problem so someone on staff definitely knows how to safely deal with Tempest CRTs.
posted by jamaro at 1:45 PM on May 9