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General Discussion / Re: Can anyone describe what a Waveform DC shift is?
« Last post by jvthorsley on November 06, 2020, 08:19:29 am »
Ah I think as has been said in this discussion, this refers to the  horizontal shift you get when there is a CMOS backup battery or high value storage capacitor in the circuit.

But you can read all the books / manuals until the cows come home, but the only way is to keep using a Tracker to fault find circuits, and in the process learn different ways of getting the best out of it.
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General Discussion / Re: Can anyone describe what a Waveform DC shift is?
« Last post by admin on November 06, 2020, 06:47:15 am »
James, what you are showing is probably more common than what krawitjr is referring to but not the same thing. He is talking about a horizontal shift of the entire signature not just the breakdown point.
Here is a simulated DC shift using the Pulse Generator on my Tracker.
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General Discussion / Re: Can anyone describe what a Waveform DC shift is?
« Last post by jvthorsley on November 05, 2020, 03:52:26 pm »
Not sure if this is the problem being discussed here.
The attached sketch shows in blue a stored signature .
Rescan and because of capacitive charge shows a shift to the right, and if this deviates beyond that set,  the test fails.
Highlight the failed signature, go into "real time",   and because of capacitor charge the trace moves to the far right.
The circuit is good, its just the instance when the signature is measured in the middle of a charging capacitor / diode circuit that can result in inconsistent results.
Or am I talking nonsense?
I use a ProTrack + Scanner + Workstation 4.3.
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General Discussion / Re: Can anyone describe what a Waveform DC shift is?
« Last post by admin on November 05, 2020, 06:42:43 am »
When you see a horizontal shift in signature position from center then there is some sort of charge level being held at that point in the circuit. It could a capacitive circuit that is holding a charge or it could be something else. In some cases, it is the Tracker that introduces the charge on the board. The amount of shift will relate to the voltage setting of the Tracker which sets the horizontal scale i.e. if the Tracker is set to 4V then you will have 1 volt/div. If you have only seen this twice then perhaps you can look closer at the circuit you were testing and you tell us.
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General Discussion / Re: Can anyone describe what a Waveform DC shift is?
« Last post by krawitjr on November 04, 2020, 07:31:37 pm »
Sorry, I cannot agree that width is in anyway synonymous with shift or offset to interpret this text as claiming the signature width increases. 

I agree offset and shift to be accurate terms to describe a the total movement (by horizontal offset alone) of a graph (I've only see the shift to the extreme left).  Again, since I've seen this affect, I'm not looking for interpretation of the text (I believe mine is accurate as it describes it as a shift).

My initial question wasn't about power (the replying posts brought that up, I never introduce that topic).  So please refrain from reintroducing power on the circuit unless that is the answer to my question.


May question is the still the same and oddly unchanged.  I will restate it here in somewhat different terms (paraphrase):

I have, twice, experienced a horizontal graph shift, during an in-circuit measurement of components, (once for a MOSFET and another a capacitor) on different items.  In both instances I saw a perfectly reasonable graph (cap=slight oval, Mosfet= Zener-like graph).  Except they were shifted to the extreme left.  But otherwise appeared normal.  Had they been about the origin...I'd have thought they were fine.  But the manual (referenced early) gives some special crediance to the shift affect I just described.

Can someone please describe to me what this shift affect (of an otherwise healthy-looking signature) means?  I know the horizontal axis is related to voltage...what would make all the voltage reads offset by an equal amount to shift the entire graph to no longer be about the origin?

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General Discussion / Re: Can anyone describe what a Waveform DC shift is?
« Last post by admin on November 04, 2020, 03:59:39 pm »
We may be running into terminology differences here in what I call "DC offset" and what that old manual called "dc shift". In reading the entire section to put it into context, it appears the old 1000 manual means a difference in signature width. Since the horizontal axis of the signature represents voltage (vertical is current), a change in the width means that the breakdown voltages of the semiconductor are occurring at a different point than what is expected (when compared to a working device). You would see this type of difference if you compared two zener diodes that have different voltage ratings.
What I was referring to as DC offset is what you see when there is a real DC voltage on the board causing the whole signature to shift along the horizontal axis.
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General Discussion / Re: Can anyone describe what a Waveform DC shift is?
« Last post by krawitjr on November 04, 2020, 01:47:03 pm »
Ok, I think I get that a non-bussed pin may have tri-state and be high impedance?  Otherwise, I don’t know what property of its internal construction makes it so special to produce this affect. 

What physical phenomenon in that situation causes the DC shift?

As I’ve mentioned I’ve seen it twice before in other components and had no explanation for what was happening.  So obviously I couldn’t properly use that observation to help troubleshoot what I was focused on.

Can a high-level company engineer or someone please explain why the graph shifts horizontally off the center origin?   I’m trying to understand electrically what the graph elements mean.
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General Discussion / Re: Can anyone describe what a Waveform DC shift is?
« Last post by admin on November 04, 2020, 06:55:07 am »
Ah, I see the information you are referencing. Again, there is no reference anywhere to testing while the PCB is powered up. However, I could see some confusion when you read this bit in section 11.2, second paragraph "Be sure the other Tracker lead is connected to ground or the positive voltage supply." In this case "positive voltage supply" is referring to the voltage pin of the IC, usually called Vcc. Vcc is referenced this way several times and I can see where it may be misinterpreted.
The "dc shift" reference in the fourth paragraph of section 11.4 is simply saying that you may see a left or right shift in the signature of a failed memory pin when compared to the same pin of another memory device. This can happen when you are using a "non-bussed" pin as your COM such as a chip enable or address strobe. Again, the shift is not caused by the board being powered up.
This old manual from 1986 does have some good and still valid information on Tracker use. Another good one is the Tracker 2000 Users manual, part number 21-1052 or 21-1229. However, range selection was totally different then and the current Trackers have a lot more flexibility.
I hope this helps.
Thanks.
Admin
9
General Discussion / Re: Can anyone describe what a Waveform DC shift is?
« Last post by krawitjr on November 03, 2020, 03:08:50 pm »
Hi,

No problem. 

Statement comes from an early tracker manual with signature examples - Huntron Tracker Operator Manual for models: 1005B-1S, 1005B-1ES, 1005B-1JS -  (Section 11.1) - Specifically 11.4 "Memories".  The last sentence of 4th paragraph was what I quoted.

I tried to attach the PDF it to this post (it's only 2.3MiB) but the forum software claims it's too big or broken or whatever, so I'm placing it on my Google drive for the time being (not forever).  Grab it while you can, it's a good read!

https://drive.google.com/file/d/1qf2eSfvAdV-V4ecmDxte5A5YWCfbC4jx/view?usp=sharing

Now before anyone starts claiming this is an obsolete tracker and not my model.  Yeah, I'm aware of that...it's also the BEST Huntron document for examples of real device signatures I've ever come across!  Much better than the scant amount in the Huntron 3200S manual or the training documents.  I highly recommend this document for anyone wanting to know what different components (like rectifiers, SCRs, etc...) actually look like on Trackers normally.

So this document off-handedly states a "stuck bus" (while powered) can be tracked for DC shift.  Please elaborate.
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General Discussion / Re: Can anyone describe what a Waveform DC shift is?
« Last post by admin on November 03, 2020, 08:21:05 am »
I think we are running into semantics here. I would not necessarily consider a memory battery to be external power. What we are trying to prevent is someone using a Tracker on a PCB that is powered up i.e. by wall power, power supply, etc. In such as situation damage to the Tracker can occur very quickly. DC offset is usually caused by very low power sources like on-board batteries and sometimes caps or super caps. Regarding a stuck bus shift, you will need to tell me where you see this reference so I can get some context.
Thanks.
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