Products > Test Equipment

New toy(?) scope Fnirsi DPOX180H, claimed 180MHz/500MSps (May 2023)

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battlecoder:

--- Quote from: csuhi17 on March 04, 2024, 09:16:38 am ---Have they already replaced the incorrectly chosen capacities in the newer sold versions?

--- End quote ---

I sold my "old" version and bought the new one a couple of months ago. I have not disassembled it, but considering what I saw in my tests after receiving the unit I don't think they did.
I didn't bother modding this new unit because even with "better" caps the problem wasn't fully gone. It was better, but still there.

I can check by opening the unit tomorrow, assuming people here are truly interested in knowing whether they made any change to the caps they picked for the new version  :-//

infino:
What's the sense of replacing it then?

battlecoder:

--- Quote from: infino on March 08, 2024, 10:15:28 am ---What's the sense of replacing it then?

--- End quote ---

Just to be clear, the problem occurs when measuring low-frequency waveforms (up to a couple of KHz) in AC coupling mode, with the probe at 10x. If you don't replace the caps, you get a severely attenuated signal under those conditions. Replacing the caps improves the situation and lowers the attenuation by a lot, making it a lot more useful in those scenarios BUT it doesn't eliminate it entirely.

After I sold my old unit and got a new one I couldn't be bothered to do the mod, mostly because I've not used the device a lot, and but also because I'm already aware of the problem so I can avoid it by not using the probe at 10x with low frequency signals if I want AC coupling.

I might still do the mod, but it's not in my priority list.

Randy222:

--- Quote from: battlecoder on March 14, 2024, 01:22:10 pm ---
--- Quote from: infino on March 08, 2024, 10:15:28 am ---What's the sense of replacing it then?

--- End quote ---

Just to be clear, the problem occurs when measuring low-frequency waveforms (up to a couple of KHz) in AC coupling mode, with the probe at 10x. If you don't replace the caps, you get a severely attenuated signal under those conditions. Replacing the caps improves the situation and lowers the attenuation by a lot, making it a lot more useful in those scenarios BUT it doesn't eliminate it entirely.

After I sold my old unit and got a new one I couldn't be bothered to do the mod, mostly because I've not used the device a lot, and but also because I'm already aware of the problem so I can avoid it by not using the probe at 10x with low frequency signals if I want AC coupling.

I might still do the mod, but it's not in my priority list.

--- End quote ---

So in this case where 10x is an issue, is it better to use 1x with a divider network? Example pic.

battlecoder:

--- Quote from: Randy222 on March 14, 2024, 05:39:57 pm ---
So in this case where 10x is an issue, is it better to use 1x with a divider network? Example pic.

--- End quote ---

Well if you want to start adding external circuitry it would be simpler to try external ac-blocking first, since it's their selection of ac-blocking cap what is questionable (although I think at one point it was determined that the ac-blocking is happening after the input resistor that forms the voltage divider with the probe, and thus it's not as simple).

Now, I don't really do a lot of AC probing. At most I use AC coupling when measuring noise in switching supplies, but the frequency in those scenarios is usually is high enough for this to not be an issue, and if they were really low-frequency (in the <10 KHz range), I still could get around this problem by not using the probe at 10x.

If I had a need to measure high voltage low frequency AC signals regularly, I would definitely prefer to mod the unit over adding external circuitry or ignoring the issue.

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