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Q&A

Oscilloscope potentially ESD striked

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I have a Rigol DS1104 oscilloscope. Last week I stood up quickly from my table and saw a spike on the scope. Right now all the channels have a DC offset when probe is connected to ground or unconnected or measuring anything. Changing the vertical scale changes the offset. At 500mV all channels show 1.2V when grounded, at 1V 680mV, at 5V it shows 4.4V etc.

I haven't noticed anything else out of usual besides this. Test signal provided by the scope works, aside from the DC offset.

To check that this isn't some weird setting, I performed a factory reset on the scope and the issue persists. The next steps would be to contact manufacturer and send it in for repair, however, I need a scope ASAP. Therefore, I am wondering how difficult could it be to repair it myself. What could be the reasons for this DC offset on all channels, and what are the chances of repairing it without sending it off?

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2 answers

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The usual culprits would rather be the ground clip itself or accidentally shorting something with it, more so than ESD. And if something has actually broken on the scope, I'd suspect the probe to be broken before anything else.

First try to calibrate the probe by hooking the ground clip to the metal terminal (bracket? I might be using the wrong English term) in the far lower right corner of the scope, then the probe to the terminal just above it. You should be looking at a perfect square wave - if not, then tune the probe until you do by using a small screwdriver. This is done by twisting a small screw on the probe itself - assuming these are probes with a square-shaped filter next to the connector, you'll find the screw of the opposite side of the text and Rigol logo.

After that, you can try to calibrate the zero offset through CH1 etc buttons then pick "delay cal" and turn the menu/intensity knob. You should notice a difference here or something might be broken indeed.


Finally, I've got some experience of using both the very model you mention as well as one of it's bigger brothers. These are not high quality products. Expect random errors to happen, there's a reason they are one of the cheapest brands on the market.

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If you're really sure the symptom appeared right after the static discharge, then something in the front end of the amplifier may have gotten damaged. However, that sounds rather far fetched. Scopes should have protection against these kind of events. Were all the effected channels connected to some equipment at the time? Is is possible that the mechanical jolt of you bumping the table caused the equipment to short the scope inputs to a high voltage?

How are you deciding there is an offset? I'm not familiar with your particular model, but there must be vertical position settings for each channel that make any offset somewhat arbitrary.

I would look in the service manual of the scope and see if there is a zero offset adjustment. You probably have to open the box to get at such adjustments. I have seen scopes with zero offset trimming capability per channel.

If the offset is too large to be able to be trimmed away, then something really did break. In that case, unless the service manual gives you a lot of detail, you need to send the scope out for repair. Nowadays, manufacturers don't supply the kind of information required for you to do your own repairs. It used to be equipment like this came with schematics, but that's not been the norm now for decades. Without a schematic, you have no hope of being able to diagnose this yourself. Even with a schematic, lots of stuff now happens inside proprietary chips that are only shown as black boxes on the schematic.

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