3406D MSO triggering issues

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Joined: Wed Aug 04, 2021 11:27 pm

3406D MSO triggering issues

Post by StephenVCahill »

I have a PicoScope 3406D MSO, serial number FP637/236, hardware version 1, driver version, firmware version It is on a USB 3.0 port of a Windows 10 Pro 64bit machine running PicoScope 6 Beta, downloaded and installed yesterday (2021-08-4). Today I have noticed several issues.

1) If I am using a custom scale for channel A with a negative gain, and am triggering on channel A using simple rising edge, when I switch to trigger on channel C, the trigger threshold for channel C has a negative threshold applied, when previously it didn't. In addition, switching back and forth between triggering on channel A and triggering on channel C results in the level of the trigger that was set for each channel changing, as if the trigger threshold was kind of carried between the two channels, but not accounting for the custom scale that is applied.
To replicate this, set custom scale for channel A to m = -1, and the units to Amps. Set the threshold on channel A to 50mA, and switch to trigger on channel C. The trigger on channel C then displays -500mV. Set the trigger to 1V. Switch back to trigger on channel A. Now the channel A trigger threshold says -100mA. It appears as if the trigger threshold is not matched to the channel, and that the polarity for the trigger threshold that is set in the custom scale is not preserved when changing channels. It would be great if each channel's trigger threshold was preserved for that channel when switching trigger channels. Maybe this is how the scope trigger is supposed to work ... but it is not best fitted for common usage models.
2) The usual way to change trigger threshold is to use the up- or down-arrows. The trigger threshold step size scales properly for a standard scale (1V/div for example) when the trigger threshold is adjusted to pass through 0. The problem is that the step size does not scale correctly when using a custom scale; passing through 0 steps the scale down by too many powers of 10 as threshold = zero crossing is approached. The step size should be consistent with the display scale setting; there's no reason to have the trigger threshold adjustment step-size step through uA and nA and pA when the scope is on a +/-100mA range. As it is, using custom scales requires typing into the trigger field when changing the trigger threshold from positive to negative or vice-versa.
3) This one is important - when changing from triggering on channel A to channel C set up as above, with the custom scale as discussed, the scope will not trigger on channel C until channel A is turned off, even if the trigger threshold for channel C is set properly. When this happens, after turning channel A off to get the scope to trigger on channel C, turn channel A back on again and the scope continues to trigger properly. This is not a trigger-level setting user-error; when I switch to channel C for the trigger and set the trigger threshold to 1V, the scope displays 1V trigger threshold for channel C, the input signal to channel C is 0 - 5V square wave, and the scope won't trigger. Turn off channel A without changing anything else, the scope clicks once and the scope starts triggering immediately. I have attached three files; one with the scope not triggering prior to the turning-off of channel A, stuck, (20210804 ChC no trigger until A is turned off.pssettings)
20210804 ChC no trigger until A is turned off.pssettings
instrument settings when should be triggering, threshold set to 1V and signal is 0 - 5V, but won't trigger, prior to turning chA off.
(3.91 KiB) Downloaded 514 times
and then another with the scope triggering again , after channel A has been turned off and back on again. (20210804 ChC triggering after A is turned off, A back on.pssettings)
20210804 ChC triggering after A is turned off, A back on.pssettings
Instrument state from when unit is triggering after chA is turned off, then back on, when initially wouldn't trigger on chC
(3.9 KiB) Downloaded 525 times
and a corresponding data file (20210804 ChC triggering after A is turned off, A back on.psdata)
20210804 ChC triggering after A is turned off, A back on.psdata
waveform captured when chA is turned off and scope starts triggering 0 - 5V signal, trigger threshold shows as 1V and should be triggering, won't until A is turned off. Captured after A is turned back on.
(20.46 KiB) Downloaded 524 times
Another clue: to get the scope to trigger properly, it isn't only changing channel A on/off that will do it. Other channel-changes will do so also. For example, if the scope is stuck not triggering on channel C, turning channel B on will make the scope start triggering on channel C.
4) This one is really important! I have noticed that there seems to be some kind of "OR" for the trigger on channel C vs. channel A. This is hard to describe, but briefly when channel A and channel C are both on, the trigger threshold for channel C does not seem to matter as long as there's a signal on channel A too; the system triggers at any channel C trigger threshold from -10 to 10V even through the channel C signal is 0- 5V square wave. It's not a glitch on the waveform that I'm not seeing that's triggering the scope; I have set the system to 2ns sample rate, 10ns/div., 8-bit no averaging, 1x scope probe (which cuts the bandwidth so no invisible glitch could get through) and no signal at or near the trigger threshold is visible where the scope is actually triggering. The system triggers with any trigger threshold for channel C over the whole available adjust range, including well outside the voltage range where the signal is present, as long as there's also signal activity on channel A. Then, if I turn off channel A, then channel C triggers properly, only over the range where the channel C signal edge is at levels where a trigger should occur; with channel A turned off then triggering stops if the channel C trigger threshold is moved outside the voltages of the signal range.
All this is occurring with Simple Edge trigger on channel C, only. There's no configuration that I can see that intentionally ties triggering together between different channels. It is possible that the chA trigger threshold is getting applied to the ChC trigger, but the scope display certainly shows the CHC trigger threshold as I move it over the -10 to +10 range, with the scope still triggering even though the input signal is only 0 - 5V.
I have attached two files showing this happening: (20210804 threshold 10V still triggers 0 - 5V signal.pssettings)
20210804l-threshold 10V still triggers 0 - 5V.pssettings
instrument settings when triggering on 0 - 5V signal but threshold set to 10V
(3.9 KiB) Downloaded 532 times
, and (20210804 threshold 10V still triggers 0 - 5V signal.psdata)
20210804 threshold 10V still triggers 0 - 5V signal.psdata
shows waveforms when scope is triggering with trigger threshold set to 10V, for a 0 - 5V signal, and shouldn't be - trigger threshold on the controls is set to 10V, outside 0 - 5V signal range.
(20.49 KiB) Downloaded 539 times
Additionally, and related to problem #3, if the scope is triggering on channel C with only channel C on, then I set the active trigger threshold to outside the range where the signal on channel C will trigger the scope, but keep the trigger set to channel C, the scope stops triggering, as expected. If then I turn on channel A but keep the trigger on channel C, setting the active trigger threshold back into the range where channel C should start to trigger, it no longer will do so, until I turn channel A off again.

When I bought this scope new I noticed some triggering anomalies, and turned in a trouble report with some example files. Specifically, I discussed this with Reggie Samples, tech support at 1 800 591 2796, at 1:10PM on 12/14/2017. My notes from that time report that if he could not reproduce the problem on the bench then he would issue an RMA number, and we would cross-ship good and bad units. The followup from him on the phone was that he was able to reproduce the problem, and that it was a software problem and would be fixed in a near-term release. I did not upgrade my software version until yesterday, though, since living with the occasional issue was better than taking the risk of losing the use of the equipment if something went awry in the upgrade. I can’t know if the triggering anomalies I am seeing today are new or a hangover from that initial problem. Either this is a new issue, or a hardware problem of some sort that has been in this unit since it was new. Either way, I'd like to resolve it.

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