3423 - Strange readings

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3423 - Strange readings

Post by FioranoCars » Mon Feb 08, 2016 11:36 am

Our 3423 while old is in good shape, and has been back to Pico for refurb (USB socket poor connection + 1 channel BNC/something else replaced - so general workshop wear and tear type things) about 18-24months ago, but we've always had, before the refurb, and straight afterwards ... and continued to have problems with symptoms ranging from:
1. getting no input at all from connected BNC's
2. Odd input (ie 8v from known and proven 12-14v)
3. Heavy noise
4. Some channels working (possibly not correctly, but getting input) other flat lining

It's almost always (and hard to remember, as never tried to correlate) when we start with the first job, ie rarely, if ever, can I remember the issue being introduced during a session.

Usually unplugging the USB (2 different PICO high quality cables), use any of the 4 usb 2.0 ports on the laptop (not a hub), or restarting the software resolves it, other times a reboot of the laptop (always running on mains power), is needed. Laptops identical except 1 has WinXPx86 (usual one that causes issues - but used for pico 99% of the time) and Win7 x64 (hard to know if this has ever had the issue, as it's used so infrequently for scope work).

So with the USB Lead disconnect issue / Crashing we've had recently, we have been a little more attentive in the "start up strange behaviour" observation department!

I'm not sure if this can make a difference, but we often plug the BNC's and connect them to the Car BEFORE plugging the USB cable in. Could this be a cause? Should we plug the USB in first? Can it make any difference?

On Saturday, we connected up to an alternator, and ChA on battery +/- was giving only 8 volts, but volt meter showed 14.1v, ChB was amp clamp, but very noisy but close to Zero, ChC was AC ripple and very noisy. Unplugged USB, rebooted just Pico, reconnected USB (BNC's remained connected) and it was working fine. It was the first Pcio task of the day, but the laptop might have been on for 4hours to 3days.

Is there some problem that was missed at the last refurb? Is this a known set of problems? Is this a Scope/Laptop/Software Issue?

While we've realised and know how to work around it (and it's become so second nature we've forgotten it's a problem!), the Saturday issue made me thing it's time to raise the matter.

Richard Lukins, with an old scope, but none the less an invaluable asset!

Steve Smith
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Re: 3423 - Strange readings

Post by Steve Smith » Wed Feb 10, 2016 3:38 pm

Hello Richard and thank you for the post.

Theoretically it should not make any difference whether the scope is connected to the vehicle( BNC end first) prior to the PC USB connection. ("Theoretically" is not the real world though)

From your description it would appear when connecting the USB to the PC first (before BNC's to the vehicle ) all is well.

My thoughts would surround the ground level inside the scope when the BNC's are connected and referenced to vehicle ground before the USB connection to the PC.

With the automotive 3000 series scopes both the BNC ground and USB ground should be at the same level, however an error here could effect the wake up process of the scope, PC communication, voltage readings and noise levels.

With all that said, disconnecting and reconnecting the USB cable "theoretically" should not make a difference and in your case, intermittently it does.

Armed with your description of the symptom I think we should inspect your scope and attempt to reproduce the condition here at Pico

Please let me know if you would like to send the scope over and I will arrange the necessary "return" details

Take care.......Steve

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