Author Topic: Rigol Scope shorting out  (Read 2543 times)

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Offline Stretto

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Rigol Scope shorting out
« on: July 23, 2017, 12:10:20 am »
I just got a rigol DS1024Z and decided to try to fix a speaker system that has issues with the main speaker not sounding(before I could hit on it a few times and it would come up, now nothing). I used connected the tip of the probe to a trace and it immediately sparked and noise was output on the working speaker. Obviously a probe shouldn't do that as it's suppose to be hi-z. Note that the ground of the probe wasn't connected, but again, that shouldn't matter. I connected a volt meter to the same spot without issue.

Pretty much all the gear is connected to the same outlet(they do come off two different power strips though, but that shouldn't really be a problem. I'm sure the scope isn't floating or much different voltage than anything else. But surely this shouldn't happen otherwise? If the probe is hi-z and it sparks on what is probably a 12-15 system, then something is wrong! The spark wasn't just a minute one from static electricity but significant(but not like it was mains).

Any ideas how to resolve this?  I was able to connect it to the input to the amplifier, which comes off the pc) and no spark
 

Offline Muxr

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Re: Rigol Scope shorting out
« Reply #1 on: July 23, 2017, 04:39:09 am »
This probably should have been posted in Test Equipment or Repairs sections.

Anyways, did you try measuring your probe with a DMM (:-DMM) to make sure you don't have a short?

Is the signal you're measuring high frequency? There could be some capacitive loading by the scope's probe at play here as well, although I don't think it would cause sparks.
 

Offline NiHaoMike

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Re: Rigol Scope shorting out
« Reply #2 on: July 23, 2017, 05:25:35 am »
A modern amplifier works with a carrier on the order of 30-50Vpp at a few hundred kHz. Could be enough to get a tiny spark into a capacitive probe.
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Offline abraxa

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Re: Rigol Scope shorting out
« Reply #3 on: July 23, 2017, 06:15:36 am »
Could it be that the probe divider was set to 1x instead of 10x?
 

Offline alm

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Re: Rigol Scope shorting out
« Reply #4 on: July 23, 2017, 08:34:49 am »
I just got a rigol DS1024Z
Are you sure this model is correct? I could not find any reference to it.

A modern amplifier works with a carrier on the order of 30-50Vpp at a few hundred kHz. Could be enough to get a tiny spark into a capacitive probe.
A few hundred kHz at 50 Vpp should be well within the limits of a 10x probe or even a scope with 1x probe. The Rigol PVP2150 is specified up to 300 VRMS from DC-400 kHz, and derated by 20 dB/decade until ~10 VRMS (see attachment). I could not find a similar graph / data in the DS1000Z manual or datasheet, so apparently that is too much effort for Rigol. A random Tek DSO was limited to 300 VRMS until 2.5 MHz, derated by 20 dB/decade to 50 V above 2.5 MHz. So neither should have had a problem with a few hundred kHz at ~18 VRMS. Assuming the DS1000Z has a similar voltage limit.
 

Offline rdl

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Re: Rigol Scope shorting out
« Reply #5 on: July 23, 2017, 10:40:01 am »
A modern amplifier works with a carrier on the order of 30-50Vpp at a few hundred kHz. Could be enough to get a tiny spark into a capacitive probe.

On the speaker outputs of an audio amp?
 

Offline abraxa

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Re: Rigol Scope shorting out
« Reply #6 on: July 23, 2017, 04:20:18 pm »
Another thought: could it be a PA system? The thread starter never specified what it is, only that it's a "sound system". So, what are we talking about here exactly?
 

Offline Molenaar

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Re: Rigol Scope shorting out
« Reply #7 on: July 26, 2017, 12:13:36 pm »
A modern amplifier works with a carrier on the order of 30-50Vpp at a few hundred kHz. Could be enough to get a tiny spark into a capacitive probe.

On the speaker outputs of an audio amp?

It might be a filterless class D amplifier?
 

Offline rdl

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Re: Rigol Scope shorting out
« Reply #8 on: July 26, 2017, 04:41:15 pm »
Obviously "a few hundred kHz" is in the audio range of frequencies so it seems like any such "carrier frequency" would be audible and probably pretty loud at "30-50Vpp". I just can't imagine any need for it. On the other hand, I can certainly imagine an amplifier putting out enough voltage to create sparks.
 

Offline Molenaar

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Re: Rigol Scope shorting out
« Reply #9 on: July 26, 2017, 04:51:52 pm »
Obviously "a few hundred kHz" is in the audio range of frequencies so it seems like any such "carrier frequency" would be audible and probably pretty loud at "30-50Vpp". I just can't imagine any need for it. On the other hand, I can certainly imagine an amplifier putting out enough voltage to create sparks.

I don't know what kind of super-bat you are, but " a few hunderd kHz" is certainly outside my hearing range :D
 

Offline alm

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Re: Rigol Scope shorting out
« Reply #10 on: July 26, 2017, 04:54:15 pm »
A few hundred kHz sounds like a perfectly sensible carrier frequency: high enough that no human will hear it and no loudspeaker will respond to it, but low enough as to keep circuit design and EMC relatively easy.
 

Offline rdl

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Re: Rigol Scope shorting out
« Reply #11 on: July 26, 2017, 07:45:26 pm »
My bad, I was seeing Hz not kHz. I guess this is must be a class D thing, because I've never seen a normal amp that needed or used a carrier frequency.
 

Online tooki

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Re: Rigol Scope shorting out
« Reply #12 on: July 27, 2017, 01:36:53 am »
My bad, I was seeing Hz not kHz. I guess this is must be a class D thing, because I've never seen a normal amp that needed or used a carrier frequency.
"Carrier" is perhaps the wrong word; "switching frequency" is more illustrative. A class-D audio amp is basically a switch-mode amplifier. At its most basic, it uses PWM at a high frequency to reproduce the signal, often with filtering to smooth it to a sine wave, but in small units, often leaving that up to the speaker drivers themselves.
 


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