Are the insides of a CRT monitor dangerous?

re: if I found my daughter dead

I'm sorry, while I accept the idea that warnings are part of life, HC you've really gone a bit over the top on this one. I'm afraid I quite agree with WA on this. If there was a real problem I'm sure we would have seen some evidence by now.

I do think the question you really mean to ask is "Legally, do we need to include warnings of possible danger in this sort of forum because of significant legal exposure if we don't?"

dan k

Yes, I was asking many questions. That was one of the main ones. But please, address the question of this thread. This reply should have been put on the other thread.

I'm all ears. If there's no danger, that goes against the consensus, so I'd love to get to the truth because I'm no expert and rely on the well educated in the field amongst us for the facts. The dangers of a CRT seems to be a question that deserves a debate.

It occurs to me that there's probably not many around right now. It's 3pm here which means it's already New Year's Eve night for most of the rest of the regulars here and many are out celebrating already. Happy New Year, one and all!

HC,
I was actually going to measure the capacitance of the 2nd anode part of a Mac CRT and estimate the stored energy, but I happened across this in the LEM:

http://lowendmac.com/tech/crt_danger.html

It seems to pretty neatly cover it. I'm going to have renounce my previous assertion about the possibility of death. It's looks very very difficult to die from a shock from the 9" CRT in a compact Mac. Maybe a bigger CRT, maybe while the Mac is actually on- then you aren't limited to the discharge pulse, as the flyback would be continually supplying juice. BTW, the HV lead from the output of the flyback to the second anode is the only place in the Mac where "high voltage" is present. The next highest voltage is gonna be in the switching power supply- something like 200-300 volts.

I'm sticking my neck out here and saying that it looks more dangerous to work around the switching supply (before the caps bleed down, or while on) or to accidentally break the neck of the CRT than it is to tangle with the 2nd anode lead.

That still doesn't preclude some darn lawyer from trying to sue your posterior in the extremely unlikely event someone gets hurt. I still think a simple, non scary, "warning" aka reminder about high voltage safety is in order when talking about working in the inside of the compact Mac.

mike

Hey,

The salient point of that article -- reading it my slanted way -- is that all the fear -- whipped up by the drama queens -- accomplishes is to send a lot of compact Macs to landfill instead of being used in some constructive way even if that salvation is merely to keep the machine alive. Can we stop with the lawyers? I mean, really. They've had decades to try a case and even the sleaziest, low-life, swamp-crawling, ambulance-chasing weasel lawyer hasn't developed a case. So can we encourage saving some vintage machines instead of scaring the be-jesus out of everybody due to ignorance and fear-mongering? Isn't that the point of places like this? To dispel false fears and keep some vintage gear alive? This notion of instant death should have been dispelled years ago and it's truly sad that we're having this conversation in this day and age.

William
www.williamahearn.com

Well, better this day and age rather than never, right? That article is dated this year. You seem to be vindicated by that article, William. Strange that my searches didn't turn that one up. Death, as in dead, seems to be the word on most lips, like on the thread I linked to before. That guy who said he watched a classmate die was either lying or referring to some other operation. He didn't actually say what the other classmate was doing, but intimated as much.

Ok, so is this the verdict? As this stands, is there a need for a warning? Someone should detail what not to do with a portable Mac in this regards.

Sorry, now I'm remembering a few here are from Oz and NZ, so New Year's Day is already a happening thing.

Hey,

Of course there should be a warning. There should also be a warning about cracking the plastic that holds the RAM in most compacts, and reconnecting the sound cable, and what size hard drives actually fit in those machines and several other things. The point that I was trying to make had to do with encouraging saving rather than trashing the cute little toasters.

Thanks for your response. I've been fighting the fear of CRTs since my days on the LEM lists and there the roar of the crowd drowned out the truth written in grease paint.

William
www.williamahearn.com

*grin* I didn't miss that point. The math looked good to me, and the point was well taken. I tried to word my previous post to convey that I don't think anyone is dyin' from working on their compact mac. I think a "reminder" like: "Don't disconnect the 2nd anode lead from the CRT without discharging it properly. It can give you a nip." should be in a take apart guide. I'll concede that it's (in light of the aforementioned article) overkill in terms of a forum discussion about opening the Mac up to change the RAM.

I don't want any more Mac's heading to the scrapheap than can be helped. Heads up's are nice, though, when appropriate.

mike

Ok, so we've addressed the question in regards to the CRT portable Macs--unless someone wants to contest the findings of that article. So now, how about other CRT's? Is it a matter of size? The larger the CRT, the more dangerous? The iMacs? The eMacs? Would any have lethal potential? Could a 22" Sony Trinitron CRT turn you into a crispy critter?

The stored energy in the CRT (when the TV/monitor is off) is a function of the voltage used on the second anode for acceleration and the size of the screen. I think the accelerating potential also increases as a function of screen size. The bigger the screen, the more surface area for the aquadag (graphite) coating, which should mean more capacitance. More voltage, more capacitance should equate to a bigger jolt. That being said, we'd need to go through the same sorta mathematics that the article did. I happen to have a couple of 21" trinitrons, and if I had a high voltage probe we could make the needed measurements.

I also don't know if all monitor/TV configurations employ a CRT with coatings set up in such a way as to form a capacitor. No clue. That'd require some research on someone's part. It'd be simpler to find the biggest CRT around, measure the second anode voltage and the CRT capacitance, and crunch the numbers. I reckon that'd be some sort of Sony Wega or something. Then we'd need to find some kinda reputable reference on death = X joules of energy in a shock. You know someone has measured that.

Sounds like fun. Lesse, that'd fall out in my to do list between "learn to play the guitar" and "dig out a new basement".

mike

So then, other than the compact macs, and the motherboard level of the CRT iMacs, your advice to anyone not trained in the field is the standard, just stay out of a CRT, especially considering there's not a whole lot a consumer has to do inside one, anyway? How about the eMac? Are the insides of an eMac to be as little feared as the insides of a Classic II? To get to the drives in an eMac, you are similarly exposed to its CRT.

It still occurs to me that we may not have addressed the dangers of a portable Mac question thoroughly. There are still some who are susceptible, are there not? People with compromised physical health, ie. a weak heart, susceptible to stroke, etc. for whom, presumably, even as minor a jolt as 46V (see my reference in the other thread) can possibly kill. In the LEM article, he dismisses this with, "...as long as you're in good enough health that you don't go into cardiac arrest when someone surprises you with a "boo!" Is this statement correct, is this an informed comment, or is he being too flippant? I would think that there are some people who could be sent into cardiac arrest by this level of shock. The 46V reference was from some periodical called "Stroke," so I would assume a lethal stroke is possible as well. Of course, what do I know? Now we could use the input from a doctor in the house. Anyway, based on the LEM article, we don't need a warning with the prevailing hysteria, but there still certainly needs to be a warning that through mishandling, the insides can produce a significant shock, correct?

I've given myself a hefty jolt across the heart while working on a Mac 512 many years ago. Less cautious and less knowledgeable, I had my hand on the metal chassis and my other hand contacted the metal of the screwdriver I was using to pry off the anode.

Hurt like heck for over an hour, but no harm done. Ten years later, and maybe that'd be enough aging to cause a cardiac arrest. Not the cause of death, but a contributing factor. Who knows.

But there's more in there than just stored voltage: Maybe not as potentially fatal, but harmful enough. I can't count the number of times I've had my hands sliced open by a sharp bit of metal, and CRT yokes can break off if you're a bit ham-fisted. 110V can do enough damage if you've forgotten to unplug the darn thing...and that can applied whether it's a CRT Mac or a clock radio.

(and to answer you, HC, as CRTs increase in size, so does the stored voltage)

IMHO, it's correct to describe any CRT as potentially fatal. Most posters here usually insert a warning whenever describing or recommending any operations in that area, but whether something like that needs to be mandated...I don't know how we could go about doing something like that other than adding it to the AUP or FAQ. It's not my call anyway.

It would be irresponsible to describe a Mac CRT anything other than dangerous and a risk for injury, even if there's disagreement as to their risk for terminal injury.

Well, really, the insides of any mains-powered object are potentially lethal if handled just right. Open the case and open the way to your (un)timely demise.

It's hard to know where to begin with the warnings, other than to suggest staying out altogether. If that were the case, why are we all here anyhow?

Specifically regarding CRTs and flyback transformers, all modern such devices are equipped with bleeder circuits that suck off excess stores of electrons very quickly. Unless one is operating on live powered equipment, this particular threat is very very minor.

By modern BTW, I mean anything Mac SE and younger. The 128 through Plus didn't include that circuit. Still, they would self discharge within a pretty short time. IIRC if I unplugged it and then pulled the case off, by that time there would be no appreciable spark given when I jumpered the anode connection to ground.

Live circuits - my electronic education included the advice that when working on live (or potentially live) circuits one should always keep one hand behind one's back. That way any exposure is very unlikely to include that fatal cross-the-body electrical pathway.

dan k