Did I break my Oscilloscope?

[jahonen]

Now, every time I turn my scope and set it on the GND coupling the trace is slightly bent. Its like I need to turn a knob that pulls the center of the trace down because the trace goes up slightly and goes back down.

To me that sounds like you'll just need to adjust the trace rotation to put the trace straight again. Try that before trying to fix anything else. Could you please post a picture what the trace looks like now?

BTW, mains should not be measured with an oscilloscope ever without using an appropriate differential probe. Reason for this is that scope chassis and input jacks are connected to the protective earth terminal on scope power plug. It is too easy to make short circuit.

Regards,
Janne

[cybergibbons]

There's a few lessons to be learnt here:
1. You can't assume that line and neutral are black and white - two pin plugs, figure-of-eight connectors into AV equipment, wiring mistakes etc. mean that they can be swapped round.
2. You always treat line and neutral with the same respect. In fact, until you know green is ground, treat that with respect too.
3. Oscilloscopes are not normally isolated - when you connect the ground clip to line, the case and everything else would have likely been connected to line.

[Simon]

that's what I was just thinking, if the scopes chassis is earthed and you connected the earth pin to live your causing a direct short circuit ?

[Mechatrommer]

Black is Hot.
White is Neutral.
Green is Ground(Earth) could also have a yellow stripe.

we use brown (life), blue (neutral), green (earth). but when its black and white... White is hot, Black is neutral.

[safarir]

Wikipedia have a great list of all the color code:

http://en.wikipedia.org/wiki/Electrical_wiring#Color_code

[saturation]

Sorry to read of this.

Its not a good idea to measure line voltage with any oscilloscope, except via a HV probe.  Its more than just the proper lines being used, good scope are very sensitive and most likely will not take transients on line voltage, transients that can be generated as simply as static atop the line voltage.  I think the Rigol 1052E is only CAT I, not more than II rated. 

An HV probe will reduce line voltage 100:1 or more, providing a wide safety margin for delicate instruments.  After all, what you want a scope to do is read the waveform, not the raw voltage, you can use a cheaper DMM for that.

[jahonen]

Sorry to read of this.

Its not a good idea to measure line voltage with any oscilloscope, except via a HV probe.  Its more than just the proper lines being used, good scope are very sensitive and most likely will not take transients on line voltage, transients that can be generated as simply as static atop the line voltage.  I think the Rigol 1052E is only CAT I, not more than II rated. 

An HV probe will reduce line voltage 100:1 or more, providing a wide safety margin for delicate instruments.  After all, what you want a scope to do is read the waveform, not the raw voltage, you can use a cheaper DMM for that.

Even HV probe is not sufficient, due to common ground. Thus if you accidentally connect the scope ground to live, short circuit results. Or if scope is itself floating, it creates a great shock hazard. There are scopes with isolated channels like Tektronix TPS2000-series to safely measure the mains directly. Most scopes require the use of the differential probe due to safety issues.

Regards,
Janne

[tayexdrums]

I appreciate the feedback from everyone. I have spent at least a couple of hours looking carefully at the PCBs. The traces around the BNC connector all look good with no signs of charring. So none of the traces are bad. Now I'm thinking its either a bad component that didn't mess up the solder pad which would make it hard to detect or the CRT is screwed up.

Jahonen: I have tried the trace rotation but the problem is that I need to bring the MIDDLE of the trace down, not rotate the trace altogether. Also, i've tried taking a picture of the trace but my camera won't pick up the minute detail.=/

[RayJones]

A good degaussing comes to mind, can't hurt to try....

[saturation]

Thanks jahonen, you are right.  It can be done under certain circumstances but its best to get a scope designed for line use.  An app note about line measurements with general DSO.

http://www.tek.com/Measurement/App_Notes/tds220-p5100/eng/40W_11342_0.pdf

Sorry to read of this.

Its not a good idea to measure line voltage with any oscilloscope, except via a HV probe.  Its more than just the proper lines being used, good scope are very sensitive and most likely will not take transients on line voltage, transients that can be generated as simply as static atop the line voltage.  I think the Rigol 1052E is only CAT I, not more than II rated. 

An HV probe will reduce line voltage 100:1 or more, providing a wide safety margin for delicate instruments.  After all, what you want a scope to do is read the waveform, not the raw voltage, you can use a cheaper DMM for that.

Even HV probe is not sufficient, due to common ground. Thus if you accidentally connect the scope ground to live, short circuit results. Or if scope is itself floating, it creates a great shock hazard. There are scopes with isolated channels like Tektronix TPS2000-series to safely measure the mains directly. Most scopes require the use of the differential probe due to safety issues.

Regards,
Janne

[tayexdrums]

Degaussing? Sounds good to me!
How do you go about doing that to an oscilloscope CRT?

[abbtech]

Black is Hot.
White is Neutral.
Green is Ground(Earth) could also have a yellow stripe.

we use brown (life), blue (neutral), green (earth). but when its black and white... White is hot, Black is neutral.

Wow that would really mess me up. Reminds me of a job I was doing where the electricians wired our entire DC system in the plant backwards (red was negative and black was positive). That made troubleshooting a nightmare since you always needed to think backwards.
The boss didn't force them to change it to save money...

[Simon]

Black is Hot.
White is Neutral.
Green is Ground(Earth) could also have a yellow stripe.

we use brown (life), blue (neutral), green (earth). but when its black and white... White is hot, Black is neutral.

Wow that would really mess me up. Reminds me of a job I was doing where the electricians wired our entire DC system in the plant backwards (red was negative and black was positive). That made troubleshooting a nightmare since you always needed to think backwards.
The boss didn't force them to change it to save money...

WHAT !!!!!!! Just tell me, roughly where do you live - I'll make sure i never set foot there

[shodan]

oh please, there is not enough energy to kill in any of the caps inside a scope

unless you count having a cardiac arrest for the surprise of being shocked

[Jamesthresher]

oh please, there is not enough energy to kill in any of the caps inside a scope

unless you count having a cardiac arrest for the surprise of being shocked

I wouldn't risk it, the heart can be stopped with only a small amount of current (in the milliamp's), It isn't worth the risk. I always employ the one hand in the pocket strategy when poking around inside anything like this (I occasionally work with large HF amplifiers where the risk is much higher). At least then if you do get a shock it won't be directly across the chest.

[alm]

I don't think there's enough charge in the CRT/HV circuit, the main danger there is injuries from the reaction to the shock, like getting the scope on your toes (and hurting your head from banging against the wall that you just destroyed an expensive piece of equipment). I wouldn't be so sure about the mains voltage power supply filter caps (if it's a switcher). But I would just stay clear of both to be safe, no point in taking unnecessary risks.

[tayexdrums]

Okay guys, so I crucially analyzed all traces and components and found nothing that is broken. I turned the scope on with the case off of it and voila! the trace was back to normal so I thought I had fixed it somehow. So I everything back together, put the case back on it, turned it on and the trace was once again slightly bent. I am so confused!!

[jinuq]

Sounds like the case is connecting two point that shouldn't be. Is there any discoloration on the inside of the case?

[Mechatrommer]

or any lose solder joint.

[RayJones]

I'll say it again, degauss the CRO.

Your lid is probably magnetised.

[allanw]

Take a picture.

[jinuq]

@RayJones, Makes perfect sense. Completely slipped my mind.

[RayJones]

Actually, magnetisation (is that a word?) can be very insidious.

I know of a colour TV set that was being used for a long period of time beneath a low metal roof.
One day the set was moved, and rotated 90deg to it's usual position and the colour purity went for a row.
It ended up being the roof had become magnetised, and over time the set established a normal balance in the environment.
Once moved, the magnetic environment was disturbed, and the electron beam in the CRT behaved slightly differently and thus distorted colours.

A once over with a de-gaussing wand seen the situation corrected.

Back to the CRO, are you certain the curved trace was not always there and the BANG mde you more observant?
Or does it change if you rotate the CRO relative to the earth's magnetic field?

[tayexdrums]

I checked the case for any signs of discoloration and found none. The scope was sold to me as "brand new and never been used" so how could it have magnetized the case already?

Okay, so you're telling me to degauss it. My dad says he has a degaussing gun but its probably from 1980 when he owned a rental business. There is no specific type of degaussing gun/wand that I should use is there?

Also, I just bought a canon power shot  SX20 IS, so I took a video of the trace and as I type this I am uploading it to youtube. So when its uploaded you can look at it for yourself.

[DJPhil]

Okay, so you're telling me to degauss it. My dad says he has a degaussing gun but its probably from 1980 when he owned a rental business. There is no specific type of degaussing gun/wand that I should use is there?

There's not much difference between degaussing tools except for size and power. They're basically a coil of wire powered with an AC signal (often line voltage through a transformer) to set up an oscillating magnetic field. You can check the case with a compass to see if it's magnetized, any needle deflection will show what areas are magnetized and how strongly. It's the alignment of the magnetic domains in the metal that constitutes magnetization.

To use a degausser just turn it on while it's a few feet away from the item in question and move it close, then away again before turning off the power. This basically scrambles up and randomizes the domains in the magnetic material, which is what you're after. Check with a compass after a pass, and repeat as necessary. Be sure to do this well away from sensitive magnetic media!

For a poor man's version you can use the coil that's built in to most CRTs (monitor or TV). Each time they're turned on they degauss with a coil that's wrapped around the big end of the tube. You'd have to hold the case near the face of the monitor, turn it on, and move the case away a couple of feet in the few seconds the coil's active. It works surprisingly well, and was often used by the folks in my father's shop in the military to demagnetize their wristwatches on occasion. Keep in mind that the degaussing coil will have diminished effect if used again quickly, best to wait five or ten minutes. It's often current limited by a thermistor, and letting the thermistor completely cool off will ensure that you get the full effect each time.

Hope that helps.