Element ELEFW40C won't turn on.

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

There are tons of useful how to do things with an Oscilloscope. There are quite a few good vids on Youtube. Search in Youtube for 'A2AEW', Mr Carlson's Lab, EEVBlog, just to get you started. Remember to be very careful with the Oscilloscope in the Primary side of a PSU, as you are connected to power mains. A normal Oscilloscope's GND on the probe is tied to the Earth pin to Mains and that is again tied together with the neutral wire in your fuse panel. So unless one puts the PSU on a isolation transformer or use a battery operated Oscilloscope, probing the wrong thing in the wrong place is going to sour your day in less than one second.

So I'm going to save up and purchase one of these isolation transformers, but it's going to take a little bit of time. Once I get it, can I probe anything on the power supply hot side? Can I put the probe on any pin or component I want on a board? Or are there things I don't want to probe? For example, if I want to look at the 120V AC that's coming into a power supply, even with an isolation transformer, would it be a horrible idea to put the probe on the hot wire there?

[Agent24]

Re: Element ELEFW40C won't turn on.

You could always get a second hand one - mine was $20.

Just check the wiring; some types are not designed for technical use, and will need the ground disconnected since it passes straight through from primary to secondary, which would defeat the purpose when using it for test\measurement.


Yes you can probe anything - provided your probe can handle the input voltage!! It may be wise to get a x100 probe with high voltage rating (like 1200v) if you want to probe the line side or PFC output (that goes as high as ~400V DC)

Obviously if you want to probe higher voltages, like those in a CRT (Some which can be ~2kV or higher, not forgetting EHT which will be at least 10kV or so, and in most cases, more) you will need a probe rated for those voltages.


Another big point to remember, something which will apply regardless of isolation transformer, high voltages or not, and which may not be immediately obvious - is that if you are probing something where what you are probing is not referenced to ground, you cannot probe something else at the same time which is not referenced to the same circuit node!

This is because all the scope inputs' grounds are connected together in most cases, and connecting the ground clip of one probe to one part of the circuit, and the other probe's ground to another, will mean you are connecting those two points together.

If that doesn't make sense, have a look at this video: https://youtu.be/pffOJdCQ7kw?t=20m10s (probably a great idea to watch the whole thing, actually)

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

You could always get a second hand one - mine was $20.

Just check the wiring; some types are not designed for technical use, and will need the ground disconnected since it passes straight through from primary to secondary, which would defeat the purpose when using it for test\measurement.


Yes you can probe anything - provided your probe can handle the input voltage!! It may be wise to get a x100 probe with high voltage rating (like 1200v) if you want to probe the line side or PFC output (that goes as high as ~400V DC)

Obviously if you want to probe higher voltages, like those in a CRT (Some which can be ~2kV or higher, not forgetting EHT which will be at least 10kV or so, and in most cases, more) you will need a probe rated for those voltages.


Another big point to remember, something which will apply regardless of isolation transformer, high voltages or not, and which may not be immediately obvious - is that if you are probing something where what you are probing is not referenced to ground, you cannot probe something else at the same time which is not referenced to the same circuit node!

This is because all the scope inputs' grounds are connected together in most cases, and connecting the ground clip of one probe to one part of the circuit, and the other probe's ground to another, will mean you are connecting those two points together.

If that doesn't make sense, have a look at this video: https://youtu.be/pffOJdCQ7kw?t=20m10s (probably a great idea to watch the whole thing, actually)

I'll watch the video. I don't understand what you mean by referenced to ground. You're talking if I'm using two probes at once though, so I should be fine if I'm always using just the one probe. But I'll use two eventually. I do have a 100x probe. I'll look at the voltage rating. The scope's specs don't matter though? It's just the probe that has to be a high enough rating? For example, no matter how cheap my scope is, with an isolation transformer and the right probe, I'd be able to probe 10,000VAC, if I wanted to?

With the isolation transformer, I'll be able to probe the 120AC coming directly into a device? That's cool. I think especially while I'm still learning, this isolation transformer should be a high priority before I attempt to use the scope again.


Now, I saw some isolation transformers that could handle higher amperage, like 4.3 amp, but they only had the 2-prong plug, not the 3-prong. I know what you're talking about with unhooking the ground on the isolation transformer. On the second side winding I think it's called. I saw a video on it. My question is if I get the 4.3 amp isolation transformer with the 2-prong plug, can I safely use that with a 3-prong plug using one of those 2 to 3 prong adapters? Would that third prong really matter at all?

This is really great information you guys are sharing. I much appreciate it! Things are slowly starting to click!

I started watching this fairly long but informative video: http://www.toddfun.com/2011/04/30/is..._transformers/

This guy seems to know what he's talking about and gives a list of isolation transformers for tech equipment, that don't require modification. I'd rather spend the money on a higher amperage isolation transformer and risk not needing the higher amperage rather than purchase the BK Precision BK1604A 1.25 amp isolation transformer I was looking at and then finding out one day I have a device that draws more than 1.25 amps.

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

So, I'm watching the video. I notice something that strikes me a bit odd. He doesn't have a square wave, but it's fairly close to one. When I put a square wave on my scope, I only see the top and bottom horizontal bars, I don't see the vertical bars. Is this normal for some scopes or does mine need some work? I've been tempted a few times to recap my entire scope. I think if I did that though, I'd need to pay someone to recalibrate it. I was thinking if I did it, I'd use those dry polymer caps, not the wet electrolytics.

I have a waveform generator. All the signals show on the scope, except one. That signal is all messed up. That means there's either something wrong with my scope or something wrong with the waveform generator. I'm leaning towards the waveform generator, because it's really old but the other signals work just fine. Maybe I should recap that as well and see if it fixes anything.

Once I get the isolation transformer, it should matter what I plug into it, am I correct? I can plug either the scope into it or the device under test. I just need one to be not sharing the same ground with the other. If I had a scope that had isolated inputs, I should still purchase an isolation transformer though, right?

Finally, I still don't understand why when I tried probing the transformer it caused sparks on my oscilloscope. I understand an isolation transformer will prevent this, but I don't understand why it happened to begin with. Could someone try explaining what went wrong?

[budm]

Re: Element ELEFW40C won't turn on.

You plug what you are working on into the isolation transformer. You must verify that your I

[budm]

Re: Element ELEFW40C won't turn on.

You plug what you are working on into the isolation transformer. You also need to verify that the line or neutral of the isolation transformer is not tied to safety GND as shown in that Video.

[budm]

Re: Element ELEFW40C won't turn on.

https://www.badcaps.net/forum/showth...541#post579541

Isolation transformer

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

Thanks Budm. I'm watching the video now and it's answering a lot of my questions. I'm at the part where he's talking about the transformers for laptops. He says the 2-prong ones are isolation transformers. This confuses me though. Just because it doesn't have that third neutral prong, I don't understand how that automatically makes it an isolation transformer. The way he says it, if I'm understanding him correctly, all two-prong transformers are automatically isolation transformers.

I think I also understand a few of my original questions. I understand why I saw sparks when I was probing a transformer on a PCB. I hooked the oscilloscope up incorrectly. Also, if I'm understanding it correctly, the isolation transformers that have the third-prong are the same as the ones that have the 2nd prong. The third prong isn't hooked up, it's just so we can plug third-prong devices into them. So, if I buy a 2-prong isolation transformer, I can use a three-prong to two-prong adapter, and just make sure I don't ground that adapter.

I received my 16760A timing and state analyzer module today. It didn't come with any probes or flying lead-sets. Now I have to figure out which probes I want to buy. These are my choices:

Accessories Agilent Part Number
Single-ended soft touch probe E5390A
Differential soft touch probe E5387A
100-pin single-ended probe E5378A
100-pin differential probe E5379A
38-pin single-ended probe E5380A
Single-ended flying lead probe set E5382A
Differential flying lead probe set E5381A

Some of these are ridiculous in price. For example, on e-bay, I see people selling the 100-pin differential probe E5379A, for 650$, another guy wants 550$. Another person wants 95$ (from Israel), 65$ from Canada.

I have to figure out which one I need though. I have some flying lead sets that I hook the grabbers to, they're not the right part number, from what I can tell. I thought they would plug into the cables coming off the module, but I was wrong. I think I need to buy something like a E5379A 100-pin differential probe and a E5381A differential flying lead set (well, two of each).

I've looked at prices and they're freaking crazy! Just a single-ended flying lead probe set (E5382A), the cheapest I can find is 386$!!!! For the differential flying lead set (E5381A), I found one on e-bay for 395$, the rest are around 1,500$!!!!!! I think I'm going to need two probes and two flying lead sets. Not sure why some probes are 38-pin and others are 100-pin either. I'm trying to google this, I've read the manual for it, but it doesn't really explain much in that sense. It's almost like it's written for someone who knows what they're doing.

[budm]

Re: Element ELEFW40C won't turn on.

"The way he says it, if I'm understanding him correctly, all two-prong transformers are automatically isolation transformers." The DC or low AC output comes from isolation transformer (but most of them will have X cap connected between Hot and Cold side so you will still get leakage current. The LINE (HOT) is still ref to GND (EARTH) of the switching (SM) circuit in hot side is still deadly if you. Neutral, Safety GND are bonded to earth GND at the panel. You touch HOT side of the circuit in the AC adapter and standing bare feet on the GND you will get shock.
The AC adapter has isolation step down transformer that is used to convert in coming AC to DC
http://hyperphysics.phy-astr.gsu.edu...ic/hsehld.html
http://hyperphysics.phy-astr.gsu.edu...ic/bregnd.html
You really need to look at the schematic of the power supply to really understand what happen when you put the GND of the scope probe in the primary side of the typical SMPS.

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

I found this in my google searching, and it touches a little bit, I still have to finish reading it, but maybe it'll provide the answers I seek. Still haven't figured out what a differential probe is though.

[vinceroger69]

Re: Element ELEFW40C won't turn on.

did a replacement board fix this tv or are you still awaiting delivery? and this is a good thread very informative as ive just got a old analoque scope so will need a isolation transformer too soon so reading the guides etc too.

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

did a replacement board fix this tv or are you still awaiting delivery? and this is a good thread very informative as ive just got a old analoque scope so will need a isolation transformer too soon so reading the guides etc too.

I'm still waiting for delivery. It's coming via USPS, and USPS's website shows it should be here tomorrow.


For the probes, I think I figured out what differential means. With a non-differential probe, I can use one ground for the entire probe, instead of grounding each and every lead. With a differential probe, I believe I have to ground each and every lead. This site gives some information:

http://www.eetimes.com/author.asp?doc_id=1265596

They show how you can see the signals of BGA components using a differential probe. I don't understand why I can't do the same with a non-differential probe though, so I still have some learning to do.

[budm]

Re: Element ELEFW40C won't turn on.

I use this at work.
https://www.picotech.com/accessories...erential-probe
No GND connection of the scope to the DUT GND, you put the two probes on what you want to measure.

[Techstar]

Re: Element ELEFW40C won't turn on.

Yes If you read safety precautions in the manual they suggest having someone there while working on one to give you cpr incase you screw up. Also it is suggested you work with one hand in your pocket so if you contact high voltage it won't go through your heart and stop it.

The current must go through the chest to kill you usually. The old saying is Volts jolts and Mills kills..

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

Okay, so I still don't understand what the difference between a differential probe and a non-differential probe is. Are all differential probes also called active probes and all non-differential probes also called passive probes?

[budm]

Re: Element ELEFW40C won't turn on.

6 hints for better scope probing.

KEYSIGHT has lots of info that can can search through.

Using scope in diff mode.
https://www.youtube.com/watch?v=VWodjUSkYVE
https://www.youtube.com/watch?v=SYaXWWAq0VY

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

Thanks Budm. I just learned what differential signaling is and I think I understand now. I still need to understand more though. I need to find some examples. I was reading and this is my understanding. With differential signaling, instead of components sharing a ground, instead of having one pin per signal, there will be two. And the component would take the difference between the two to figure out what the actual signal is, so things like noise wouldn't be a factor anymore. I will read the links you sent, maybe I'll have a better understanding of it.

I've actually been reading a lot of documents from KeySight and been in communications with one of their workers, Al. He's very knowledgable and helpful.

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

So maybe you can help me understand a little bit more.

Let's say we have a differential signal, and we have a component that expects that differential signal and has two pins for that signal.

We can call one of the pins DSa and DSb (for Differential Signal A and Differential Signal B).

Something sends out a differential signal and sends a +2.5VDC pulse down DSa's trace and a -2.5VDC pulse down DSb's. The component would see a +5VDC pulse, right?

How does this prevent noise though? Let's say we have the same setup, but this time something sends out a differential signal and sends a +2.5VDC pulse down DSa's trace and a -2.5VDC pulse down DSb's trace. But this time, on the DSb's trace, we pick up some noise and the component, instead of seeing a -2.5VDC, it sees something like -2.8VDC. Wouldn't the component actually see +5.3VDC?

[budm]

Re: Element ELEFW40C won't turn on.

I.E. Diff input of OP amp, it will reject common mode noise.
https://en.wikipedia.org/wiki/Differential_amplifier
https://www.omega.com/techref/das/se-differential.html

Audio Equipment using balance INPUT/OUTPUT is another example.
LVDS in your TV is another example.

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

I got it! Thank you!!! Al also helped explained some of it to me as well Budm, I was struggling with understanding how differential signaling reduced noise. I thought it completely prevented noise, but I guess it just makes the circuit less susceptible to it. My understanding is the differential signals are going to be ran so close that if there is noise, it'll be on both lines and that's why it won't matter so much. It's all starting to click!

Right now, I should be looking at purchasing two of the following:
38-pin single-ended probe E5380A
Single-ended flying lead probe set E5382A

Then, eventually, I'll be working on purchasing the differential flying lead probe set. I might have misunderstood. I was thinking the flying lead probe set plugs into the single-ended probe (E5380A). I think that might be wrong. I think the E5380A is for boards that have a connector that the E5380A plug directly into. I think I might just need two E5382As and maybe two of the differential flying lead probe sets eventually.