X-rays and you?

[Dave Wave]

So I am working of my game with the monitor running, my head pretty close to CRT, which is ruiing on its merry way, and I start thinking about the warning in the operators manual about X-ray hazards if the unit is "out of adjustment". What exactly goes wrong to turn a CRT into an X-ray machine?

Am I glowing?

-Showtimne

[Ken Layton]

Since 1970 all tv sets and monitors have an xray protection circuit built-in. If the high voltage climbs to 30,000 volts or more the power is shut down preventing xrays from occuring.

[Dave Wave]

So that protection would have to fail to produce Xrays...hence the Horizontal Oscillator disable test on my Matsushita 202G (although it looks at the heater voltage going above 10v).

Have you ever heard of one going bad and nuking somebody?

-Showtime

[Level42]

Well, you could always ask some x-ray film from your local hospital, hang it behind you while playing in front of the CRT and see if anything gets on it

Not sure, what Ken says is correct and I don't think there is a way to get that protection mailfunctioning unless deliberatly. However, I do think every CRT still produces a small amount of radiation. Very small indeed. I think I remember reading somewhere that a single transatlantic flight subjects you to more radiation than watching TV for a whole year. Or something like that.....nothing to worry about...

[Rickn]

Hi Guys, here is the real scoop.

In the very early days when tV's and monitors used vacuum tubes, FDA (food and drug administration) and DHHS (Department of Health and Human Services) put into effect CFR part 47.
This regulates the possibility of a picture tube as a raw componet and when used in a monitor to emit X-radiation.

A tube manufacturer is required to sample their production using High Voltage supplies that can produce in excess of 50,000 volts.
They measure the amount of x-radiation emitted using a Victoreen Survey meter. They must record when the tube submits .5Mr/hr- this is normally in excess of 50,000 volts.

Strict records are kept and anual reports are required.

When we as a monitor manufacture build the monitor we must comply by submitting a huge engineering report, we must sample a monimum of 1 monitor per day per production line per shift ...
By the way we must take action if even ,1mr is emitted.

When we export into the USA it is even stricter than if we build there as every monitor requires a certificate indicating we have complied with all this.

Anyway, most of this is really an out of date formality.

I say this because:
- Ken is partially right, but there is not a requirement for all monitors to have the shutdown circuit.
- During the original engineering report we are required to create a special chassis that has all of the worts possible conditions including worst tolerance components, component failures such as shorts and opens...

Bottom line is I have never seen a modern board (I have been doing this for 25 years) even get close to the 50,000 volts for the tube to emit x-ray, the flback just cannot get there and even if it could fuses, resistors etc would open.

The closest I have ever seen to this was with a projector years ago at Electrohome where the tube manufacture did not apply a lead tape shield inside the tube. The tube emitted radiation but well within limits.

All this said, it is extremely unlikely- and I stop short of saying impossible, (I gave up in saying aything is impossible) that you have to worry.

Hope this helps.

Rick Nieman
Nieman Video Displays
Rick@niemandisplays.com

This is because of 2 things

[Level42]

Hey Rick,

Thanks for all that info ! Didn't know testing was that tight, but it's probably there for a reason

Just had a look at your site, and at a point I actualy thought you were based in Cambridge UK....but regretfully for me it's Canada....

Who's your European distributor ?

[Rickn]

Sad to say we have no one in Europe, this is primarily due to 2 reasons, transportation costs and a new regulation placed on most electronic devices this past July that restricts the amount of lead content allowed anywhere in the monitor.
This includes even the smallest of components right down to the pins of an IC.

If you have any insight on how the new RoHS regulation is being handled there, it would be greatly appreciated.

Rick