Dangers of the CRT ??

[srieck]

I have no intention of monkeying with CRTs but I want to recap my se/30. I am technically proficient with Mac repairs but I have a wife and two boys and I generally enjoy life more than playing greyscale asteroids...

So just how dangerous are these specific CRTs on the SE and SE/30? Are people killed by these things?

I understand how to make and use the discharge tool so I don't need a lesson in that stuff. I'm just curious of the risk involved.

Anyone here been zapped and lived to tell?

 

[Unknown_K]

You don't have to do anything with the CRT to remove the main board on an SE/30. You hand will be on the CRT side to remove a couple cables but not close to anything that will shock you. Worst thing you can do if you are a clutz is break off the back of the CRT tube.

 

[srieck]

The answer I've heard is VERY dangerous and people are killed....in which case how is it that all you guys seem to recap your boards?

 

[srieck]

Ok thanks ...didn't see that response.

 

[MacJunky]

Because most of the people who say that people die left and right because of CRTs are spouting misinformation.

It is not so much high voltage that kills, it is more the amperage. If any high voltage killed you just like *snaps fingers* then there would not be taser survivors or lightning strike survivors.

If you are 90 and have a wonky pacemaker, sure, stay away. Otherwise, meh, go at it.

 

[srieck]

And where exactly are the danger spots on the CRT?

 

[srieck]

What is the amperage on these and how much is lethal?

 

[Mk.558]

They are high voltage, low amperage.

I have opened Compact Macs many times (as have others). I, like many others, have had no problems.

Straight talk: Act responsibly, and you won't ever have a problem.

There is no need to discharge the CRT if you are popping the motherboard.

There are four cautionary notes about the CRT: 1) Implosion hazard [high vacuum], 2)High voltage, 3) Burn-in [overexposure to a single picture], and 4) Too much time spent in front of it giggling at icanhazcheezeburger.com.

1) Implosion hazard: Simply don't drop it or smash anything against it. The area near the back of the yoke is a bit weak, but just see the previous sentence to avoid this.

2) High Voltage: Discharge before removing or working with the CRT. Simple. You won't need to do this for the motherboard.

3) Use a screensaver -- the quintessential After Dark: Starry Night does a good job of this. (Newer CRTs are not as vulnerable to this)

4) ...Have fun.

EDIT: Most (if not all) SE/30 CRTs have a bleed resistor which drains the residual voltage after powering down. If you're still hyperphobic, turn the machine on, set the brightness knob to the max, then yank the plug (not the power off switch, pull the plug hot).

 

[Scott Baret]

The "danger spot" is the anode cap, which looks like a large red suction cup. It can only fry you if the machine is plugged in. As Mk. 558 said, most newer CRTs will self-discharge. I believe all Classics, SE/30s, and SEs with newer analog boards will self-discharge. (I've heard conflicting reports about 1984-1987 manufacture Macs, so for those I usually just leave them unplugged for about 3 days; never have had a problem with one even when working on the CRT). I never use the actual discharge tool.

You won't be anywhere near the anode cap with the work you describe. If by some chance you do need to ever replace your CRT, you should be fine as long as the machine is unplugged. I've done tons of work with anode caps inside these Macs (which has involved touching them) and have yet to even feel the tiniest shock.

The area where you want to use caution is if you're ever adjusting a "live" CRT's geometry (that is, positioning the centering rings, adjusting the yoke, or fiddling with the square magnets around the CRT's neck while the machine is on). Again, just use common sense and caution--avoid the anode cap and analog board (some components can give you a jolt when it's on--know this from experience) and be careful with the positioning of your hands.

 

[srieck]

Yes I've seen there'd suction cup...so

You're saying I should resist the urge to lick that when the machine is on...no matter how tempted I get? Lol...

Anyway my real question is based on experience with high voltage with big caps inside guitar amplifiers where it is said you can actually be zapped by other places in the circuit somehow...there's no chance the voltage that is associated with the anode can somehow get somewhere else in the circuit?

 

[Concorde1993]

Srieck,

If you don't know what you are doing, or are afraid to venture inside a Compact Mac, let a trained TV technician recap the analogue board. I did that with one of my compacts (which developed the bright vertical line syndrome), and the cost was under $60 w. labour (I have no experience with soldering, and I, too, was a little weary of opening the case on my compacts). Besides, you get a warranty for all repairs done on the machine (just try and find a reputable technician- and yes, they are becoming harder to find unfortunately).

A good technician may guide you through how to discharge the CRT if you ask so you can complete your own repairs. I took the initiative, and it's really not that difficult (just try not to hit the yoke, or else it's game over for that display, and you don't really want thousands of pieces of glass flying around everywhere, although I do believe that some of the CRTs in the compacts had an implosion safety feature of some sort- one of my upgraded Pluses has a label which states that, although I wouldn't trust it).

 

[techknight]

I could be wrong, but if im not mistaken, i think the flybacks in these things have a bleed-off resistor so when the power is off, the CRT self-discharges.

 

[phreakout]

Srieck,

I've been recapping logic boards on SE/30s for a couple of years now. There are times where I have operated my SE/30 without the case plastics on and disassembled the machine shortly after power down. I think the chances are pretty slim for getting shocked by these compact Macs. The later models have been given enough amble protection against high voltage contact compared to earlier ones. Now I think the risk goes up only at times when you do have to troubleshoot or adjust things on the analog board or crt and yoke assembly. For these, just make sure you don't use both of your hands; the chances of having high voltage go from one arm, across your chest and exiting your other arm will be lessened. Just place one hand in your pants pocket or hold it behind your back as you make adjustments or take multimeter readings.

73s de Phreakout. :rambo:

 

[srieck]

I think analog board looks ok...there is a sound issue in that I have none except a very faint signal from the headphone jack. I assume this is most likely a cap on the logic board.

The official take-apart guide indicates removing the display board on the CRT to get the logic board out.

Could someone describe the most effective method for getting the logic board and hard drive out? Preferably staying out of the way of the CRT?

 

[Scott Baret]

First, I think we need to understand "analog" vs. "logic" board, as these terms seem to be flying around here at random.

The "analog board" is sometimes referred to as the "vertical board". As this nickname implies, it is mounted vertically when the Mac is sitting upright. This is the board to which the power supply is attached (it's actually one unit in non-SE form factor Macs). It mostly controls the power and some video functions.

The "logic board" is sometimes called the "horizontal board". It's essentially synonymous with "motherboard" in description and function, which I'm going to assume is a term familiar to you.

Next, the procedure to remove the logic board and hard drive:

1. Open the Mac. Set it down on a towel, remove the four Torx T-15 screws (two in the shaft, two near the ports). You'll need a long-shafted T-15 screwdriver to do this. These are usually available at Sears (if you can't find one, send me a PM and I can pick one up at my local Sears, which I know has them). Separate the case. Don't use a screwdriver or anything similar to do this, simply pry it apart gently at the seams as not to crack the case.

2. Remove the following from the logic board: floppy cable, hard drive cable, analog board cable. Next, pull the board up from the chassis. You will find it has a series of indentations on the right side, which you can use to remove it. As you remove it by lining these up with the gaps in the chassis, disconnect the speaker wire from the board.

3. To remove the hard drive, you can unscrew the two Phillips head screws of the hard drive bracket from the top of the floppy cage (there is one screw on either side) and pull the bracket out. Make sure you disconnect the hard drive power cable. Be careful when pulling this out as not to damage the CRT or video board (connected to the CRT's neck).

 

[srieck]

Very helpful! Thanks everyone.

One final question - assuming the machine is not physically plugged in (and therefore off), is the only really dangerous part the actual anode (red auction cup thing) ?

Are parts of the analog board, other parts of the LCD or possibly even the chassis potentially dangerous when the machine is off?

 

[Concorde1993]

Are parts of the analog board

The capacitors on the analogue board are known to still retain their charge for over an hour after being unplugged.

If you really want to play it safe, and not physically discharge the CRT, let the Mac sit for about a week unplugged. By then, most of the current should have dissipated.

 

[phreakout]

Srieck,

I think you should be perfectly fine. Later versions of the compact Macs (SE through Color Classic II) will have a bleed resistor attached inline with the anode cap and flyback transformer or just in series with those 2 parts. The whole purpose of the resistor is to quickly dissipate the remaining high voltage. And by quickly, I'm talking as soon as you flip the power switch to turn your Mac off. I believe all the dangerous levels will be gone within a minute. I know that seems like a very conservative value, but not once have I gotten zapped right away when working around the high voltage areas.

The parts with the highest possible potential for shock hazard is the CRT, anode cap/flyback transformer (anode cap all the way back to the metal cage), some of the larger capacitors and the power supply unit. I think the power supply unit has the greatest shock hazard of all since you are dealing with higher current (amperes) than the rest of the machine. You have the highest amps from the AC power coming in through the power cable (about 10-60 amps) and then it starts dropping as the voltage is changed and distributed out of the power supply to where it needs to go. The power supply will output your standard 12 and 5 volts DC and the analog board will raise some of that to a few hundred volts and up.

One thing to add: Scott Baret didn't mention not to forget to remove the plastic Reset and Programmer Interrupt Switch on the left hand side of your Mac before you pull the case apart. You're not the only one who has forgotten about that.

73s de Phreakout. :rambo:

 

[tomlee59]

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

Short version: If the ac cord is unplugged, danger of lethal harm from a compact mac's crt is extremely low. It's not so much volts or amps, it's a function of the energy delivered to your delicate parts. And that energy is not high.