DC offset stuck at -650 mv

Logic MSO
1

^ for at least yellow and green analog probes. Adjusting in software does nothing.

2

@slagernate Strange… I’m not immediately sure what could be causing your offset to be stuck. Adjusting the Offset value in the Device Settings panel on the right should immediately change the offset (change value > press Enter).

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I have some follow up questions below to try and get to the bottom of this:

  1. What version of the software are you using? (as of today, the latest is 2.4.44)
  2. Can you describe what exactly happens when you try adjusting the Offset value?
  3. Can you drag the analog waveform up and down? This should also adjust the offset value automatically.
  4. You mentioned that the issue is seen with the yellow and green analog probes. Are you implying that the Blue and Pink probes (CH3 and CH4) are able to be adjusted successfully? (assuming you own our 4CH model)
3

While running 2.2.43 I left the MSO running for a few days and the offset for all channels (1 thru 4) was clipped at negative rail regardless of set range (e.g. even with kV scale, was clipped at negative rail).

I power cycled the device and still see offset on Ch1 and Ch2. No offset on Ch3 and Ch4. It seems to scale with the input range (~-500 mV for 5 V input range on Ch1, ~-650 mV for Ch2). Notably, using the software offset works for Ch3 and Ch4 but not for Ch1 and Ch2.

I’ve updated to 2.2.44 just now and still see this behavior even after power cycling.

4

Ok now I’m confused. I did one last test to adjust offset on Ch3 but now it appears to not budge.

Also tried “dragging the analog waveform up and down” and nothing appears to happen?

5

@slagernate,

Sorry for the trouble with the device!

First off, this sounds like some kind of hardware failure, and we can replace it under warranty. We ship the replacement first, so you can hold on to your existing unit until the replacement arrives, so you won’t have any down time (besides only having 1 working channel for a few days).

Please write in to support, include a link to this post, and also include your device’s serial number, model, and order information if you ordered it directly. Also include your shipping address and phone number: Contact Us | Saleae

Tim will help manage the RMA process.

It seems like the only clue is that you left it running for a few days. This should be fine of course, but we’ll want to try and replicate your situation as closely as possible. Could you answer a few questions for me about that setup?

  • When it was running for days, was any signal connected to the inputs? (anything besides inputs floating) If so, can you describe that signal? (e.g. constant DC voltage, or some sort of analog signal, etc. Anything you can share that would help us replicate that, perhaps using a signal generator)
  • When it was running for days, were you using the software at all? If not, do you recall approximately what settings were in use over that time? (ideally range and offset, specifics would be ideal but generalizations are OK. mainly looking to know what the vertical zoom level was (full scale range in volts) and what the vertical offset was.
  • You mentioned the inputs were clipping at at the negative rail, even at the kV scale. Is this what you observed at the end of the period, or was this happening the whole time? Main question i have here is if this problem developed over the multi-day period, or was a problem before it started.
  • Please share anything else you think might be useful.