Xray hazard?

Bangback

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I had an issue with a WG 19" K7000a chassis with a zenith flyback. Put in a cap kit, and transplanted a good R103 from another chassis.

After putting it back in, the monitor would go into shutdown after a few seconds.

Took it back out, removed the epoxy off of the HV shutdown pot, put it back in, and adjusted it so the monitor wouldn't shut down anymore.

Picture is now perfect, crisp and bright, and stays on all the time.

Is there any possibility of xrays coming out the tube now since I messed with that pot? Is there something to check with my meter to make sure it's within limits? I'm sure the epoxy was on that pot for a reason.
 
no that circut is there to keep x-rays from getting to you. adjusting that pot is sometimes nessary to get it out of HV shutdown.

you are ok and that chassis is good to go till the flyback craps out.

Peace
Buffett
 
The purpose of the HV shutdown circuit is to limit HV to the tube so excessive x-rays aren't generated. If your monitor is going into shutdown, either the HV is to high or the shutdown circuit is not functioning properly. Given the age of these monitors, it could be either.

Blindly tweaking the shutdown circuit to make it work is not a good idea because you don't know if you just corrected a circuit drift or disabled a properly functioning safety mechanism. It's not a huge risk, but I would recommend that you check the HV levels with a probe after making any adjustments to the HV shutdown circuit.
 
If obtain a HV probe, what would be an acceptable reading or range?

Is there a rule of thumb that says if the HV is past a certain point, then X-Rays are being transmitted at a harmful level? Would this only apply to 19" WG's or across the board to Electrohome's, Sanyo's, etc?

The radiation meters seem expensive, so this looks like the best way to gauge how much of it may be coming out?

Sorry for all the questions! I just don't want to glow in the dark after my game is turned off...
 
First, don't panic. It's not a huge issue if you're a couple of KV off. The fly pots move it more than that in normal use, and you'll probably be dealing with retrace lines long before x-rays. But you don't want to be driving a 19in tube at 50KV or something nutty like that.

If obtain a HV probe, what would be an acceptable reading or range?

To be 100% certain, match the specs on the monitor schematic. 19.5KV for a K7000 IIRC As a rough rule of thumb, 1KV per inch of tube, but I'm not certain if that scales properly at larger sizes.

Is there a rule of thumb that says if the HV is past a certain point, then X-Rays are being transmitted at a harmful level?

I've seen some numbers published, generally in the > 35-40KV range, but it depends on a lot of factors. CRTs have built in protections like leaded glass and HV shutdowns so the risk is extremely low. I mentioned it because you tweaked the shutdown pot blindly, and without knowing the range of that circuit, there is a risk. It could very well be that the upper limit of that pot is well below the limit at which you should be concerned.

Would this only apply to 19" WG's or across the board to Electrohome's, Sanyo's, etc

Brand/model does not matter as all CRT's produce X-rays. Arcade, TV, oscilloscope, baby monitor, etc.

The radiation meters seem expensive, so this looks like the best way to gauge how much of it may be coming out?

That would be SERIOUS overkill. At normal operating voltages, the risk is near zero. I just recommend it to be sure your HV circuit wasn't kicking in because your fly was putting out way too much voltage.

Sorry for all the questions! I just don't want to glow in the dark after my game is turned off...

Take a deep breath and relax. Worst case scenario, it's putting out more than normal and/or is recommended. And even those specs are based on "typical" daily use, and not "once a week for 20 minutes" use. besides, if you turned your CRT into a portable x-ray machine, your flyback won't last long enough to matter anyway...
 
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I was joking about glowing in the dark. :)

That's great information! Thanks for posting that!

I'll look into getting a probe and seeing how much is coming out.
 
I don't think so? The picture seems about perfect.

I adjusted the brightness, contrast on the board, and also the brightness on the back of the flyback so that it isn't too bright. Adjusted the other pots to make the picture fit on the screen.
 
I don't think so? The picture seems about perfect.

Here is an example of retrace lines. Typically caused by screen voltage too high. If you've got a perfect picture at normal brightness, I'd put checking the HV on the "when I get a chance" list.

Unless of course you're like me, and this presents a great opportunity to purchase another tool. If that's the case, then by all means do not risk your family's safety over a few $$, go get a probe man! :)
 
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