Rigol Scope shorting out - Page 1
Forum section: electronics / projects

author: Stretto
author_rank: Newbie
timestamp: July 23, 2017, 12:10:20 am
content: 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

author: Muxr
author_rank: Super Contributor
timestamp: July 23, 2017, 04:39:09 am
content: This probably should have been posted in Test Equipment or Repairs sections.Anyways, did you try measuring your probe with a 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.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 23, 2017, 05:25:35 am
content: 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.

author: abraxa
author_rank: Frequent Contributor
timestamp: July 23, 2017, 06:15:36 am
content: Could it be that the probe divider was set to 1x instead of 10x?

author: alm
author_rank: Super Contributor
timestamp: July 23, 2017, 08:34:49 am
content: Quote from: Stretto on July 23, 2017, 12:10:20 amAre you sure this model is correct? I could not find any reference to it.Quote from: NiHaoMike on July 23, 2017, 05:25:35 amA 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 VRMSfrom 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 VRMSuntil 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.

author: rdl
author_rank: Super Contributor
timestamp: July 23, 2017, 10:40:01 am
content: Quote from: NiHaoMike on July 23, 2017, 05:25:35 amOn the speaker outputs of an audio amp?

author: abraxa
author_rank: Frequent Contributor
timestamp: July 23, 2017, 04:20:18 pm
content: 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?

author: Molenaar
author_rank: Regular Contributor
timestamp: July 26, 2017, 12:13:36 pm
content: Quote from: rdl on July 23, 2017, 10:40:01 amIt might be a filterless class D amplifier?

author: rdl
author_rank: Super Contributor
timestamp: July 26, 2017, 04:41:15 pm
content: 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.

author: Molenaar
author_rank: Regular Contributor
timestamp: July 26, 2017, 04:51:52 pm
content: Quote from: rdl on July 26, 2017, 04:41:15 pmI don't know what kind of super-bat you are, but " a few hunderd kHz" is certainly outside my hearing range

author: alm
author_rank: Super Contributor
timestamp: July 26, 2017, 04:54:15 pm
content: 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.

author: rdl
author_rank: Super Contributor
timestamp: July 26, 2017, 07:45:26 pm
content: 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.

author: tooki
author_rank: Super Contributor
timestamp: July 27, 2017, 01:36:53 am
content: Quote from: rdl on July 26, 2017, 07:45:26 pm"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.