Hantek6254BC - Dubious voltage readings - Page 1
Forum section: electronics / testgear

author: DarkBabylon
author_rank: Contributor
timestamp: May 04, 2018, 04:59:22 pm
content: Hello, I've recently acquired myself a scope. Quite the beast, 1GSa/s, 250Mhz bandwidth, 4 channels. So far with what I could work with, it works great.However something...unusual happened... It seems like I am getting addition voltage from somewhere and can't quite figure out what is wrong.It only seems to happen when I change Voltage division settings. So, running on a win10 machine, for a 1V/Div I get this following picture:Hmmm, it seems like there is an addition 1 volt from ground when connected to the square signal for probe compensation. 2Vpp, 1kHz, as it should, but Vmax is 3 volts.Let's try a different setting, 5Volts/Div:'Wait... where did the square go?' I asked myself, realizing the signal got high... might as well be a man on drugs because now it reads 22.4Volt max. Also got noisier which is not at all surprising...I have no clue what is happening, and can't get to hantek, their filtering seems to classify my Emails as spam, and I have yet to contact the seller because I presume it could be an error on my part.What I did find is this: The probes themselves do not seem to experience 20 volts boosts, so on that part we are fine and dandy, at least I can connect stuff to it safely.There seems to be a switching regulator for negative 5 volts, and don't think it would be coming from there, but I have not done a proper noise test for it...There are coil relays apparently, or something else that makes similar noises on the board, but that would require a proper teardown and don't want to mess with the hardware quite yet.So the options at the moment:1) The data is not transmitted properly either due to the brains of the scope or the software interpreting it badly2) There IS a 20 volt boost somewhere.What could I do? did anyone stumble upon this error?

author: thm_w
author_rank: Super Contributor
timestamp: May 04, 2018, 07:21:49 pm
content: Do you see the same offset using DC coupled mode?

author: gf
author_rank: Super Contributor
timestamp: May 04, 2018, 07:26:06 pm
content: Before running auto-calibration for the first time on my 6074BD, I facedhugeoffset errors. Did you already try to inovke the calibration procedure for each of the 4 channels?

author: DarkBabylon
author_rank: Contributor
timestamp: May 04, 2018, 07:59:14 pm
content: Actually, yes, both DC and AC. Only GND puts it to zero, but for some reason takes away signal.

author: PA4TIM
author_rank: Super Contributor
timestamp: May 04, 2018, 08:59:57 pm
content: QuoteYes, that is correct. It disconnects the signal and shorts the input to ground. This was important for analog scopes to set the trace at a known 0V reference position.I do not know the scope but some scopes have the possibility to add a DC offset.

author: DarkBabylon
author_rank: Contributor
timestamp: May 04, 2018, 09:07:55 pm
content: Quote from: gf on May 04, 2018, 07:26:06 pmD'oh! Shoulda read the freakin' manual! It mentions it.I calibrated it, now it is a nice around 0 volts, 2Vpp signal.Thanks everyone.Can't wait to start testing this baby at RF.Quote from: PA4TIM on May 04, 2018, 08:59:57 pmYou learn something new everyday.

author: gf
author_rank: Super Contributor
timestamp: May 04, 2018, 09:29:20 pm
content: QuoteThis one does not. I'm not even sure, that GND really connects the analog input to ground - my feeling is that it just fakes a zero signal digitally, when the switch is at GND position (that's why analog offset errors don't show up in the GND position).gf