I have never used an oscilloscope and don't know how they work

[orientalsniper]

Hello all, so I just bought a DS1054Z (http://www.rigolna.com/products/digi...1000Z/ds1054z/) to help me assist repairing laptop/desktop motherboards.

I'm basically this right now:



I could use some pointers or any site that might help me introduce to this new instrument.

[stj]

Re: I have never used an oscilloscope and don't know how they work

http://www.ionpool.net/arcade/scope_files/scope.html

[smpstech]

Re: I have never used an oscilloscope and don't know how they work

All I can tell you about Scopes is that careful with what you connect your Ground Wire to on the Scope probe. With SMPS's you can blow stuff up.

[popeye]

Re: I have never used an oscilloscope and don't know how they work

Look for EEblog on youtube Dave Jones site

[orientalsniper]

Re: I have never used an oscilloscope and don't know how they work

All I can tell you about Scopes is that careful with what you connect your Ground Wire to on the Scope probe. With SMPS's you can blow stuff up.

How so?

Btw, thanks for the suggestions.

[budm]

Re: I have never used an oscilloscope and don't know how they work

You plug what ever you are working on into isolation transformer (both Hot and Neutral on the output winding are completely floated/not connected to the safety ground).

[keeney123]

Re: I have never used an oscilloscope and don't know how they work

We just use to cut off the ground pin that plugs into the receptacle will that not work?

[budm]

Re: I have never used an oscilloscope and don't know how they work

We just use to cut off the ground pin that plugs into the receptacle will that not work?

If you touch the chassis of the scope when the probe Ground lead is attached to the primary side of the circuit ground ref. you are working on, the chassis of the scope is now at hot potential and you can be electrocuted.

[popeye]

Re: I have never used an oscilloscope and don't know how they work

HI

Just watch this. Here

[Uniballer]

Re: I have never used an oscilloscope and don't know how they work

We just use to cut off the ground pin that plugs into the receptacle will that not work?

Other than budm's safety objection, this will work on older scopes with linear power supplies. But newer scopes with switching mode power supplies cannot be isolated from ground so easily because they are generally capacitively coupled to the power line. You will need to use a transformer to isolate the unit under test (or scope if you insist) in that case.

[stj]

Re: I have never used an oscilloscope and don't know how they work

one other thing not mentioned is that most low-end scope probes are only rated for 300v

[Compgeke]

Re: I have never used an oscilloscope and don't know how they work

one other thing not mentioned is that most low-end scope probes are only rated for 300v

My 'scope itself is only rated for 300V and it (was) a higher end Tektronix - a TDS684B.

[stj]

Re: I have never used an oscilloscope and don't know how they work

ah, but if you have a x10 probe...............

[keeney123]

Re: I have never used an oscilloscope and don't know how they work

If you touch the chassis of the scope when the probe Ground lead is attached to the primary side of the circuit ground ref. you are working on, the chassis of the scope is now at hot potential and you can be electrocuted.

If the ground on the plug is cut off so it does not attach to the electrical ground the scope will be floating. We use to have a problem when I work for Gerber Scientific Produces with the a power board that drove a New Hermes Computerize engraving machine. The Lead Research Engineer Buddy Rich cut off the ground plug so we would not blow fuses when we attached the ground clip of the scope. Buddy Rich had attended Harvard and he wrote the loop equation for servo motors. I may not be understanding this right but it would seem this would fix this problem unless they are making the Tektronix scopes different than in the 1980's.

[budm]

Re: I have never used an oscilloscope and don't know how they work

Cutting the Ground of the power plug of the scope will stop the damage (blow the fuse or smoke) to the scope of or what ever you are working on when the Ground probe of the scope (which is also connected to the chassis (safety ground, some time the circuit ground of the scope is connected to the chassis through low Ohm (10~100 Ohms) resistor) of the scope, BUT the chassis now will become HOT, it is safety issue, not the blow up issue when Ground prong of the power plug is cut.
If you draw up the SCH of the line operate power supply of the primary side circuit, you will see the current path when you attach the test equipment to the hot side of the circuit, for example the scope probe on the primary side ground ref point which will be the negative leg of the filter cap. It will explain a lot when you analyze the circuits.
It is hard not to make contact with scope body when you have to make any knob adjustment.

[keeney123]

Re: I have never used an oscilloscope and don't know how they work

You may find this interesting. The attached file is from Tektronix and floating grounds. They say the using a isolation transformer is just as bad as cutting the ground plug.

Cutting the Ground of the power plug of the scope will stop the damage (blow the fuse or smoke) to the scope of or what ever you are working on when the Ground probe of the scope (which is also connected to the chassis (safety ground, some time the circuit ground of the scope is connected to the chassis through low Ohm (10~100 Ohms) resistor) of the scope, BUT the chassis now will become HOT, it is safety issue, not the blow up issue when Ground prong of the power plug is cut.
If you draw up the SCH of the line operate power supply of the primary side circuit, you will see the current path when you attach the test equipment to the hot side of the circuit, for example the scope probe on the primary side ground ref point which will be the negative leg of the filter cap. It will explain a lot when you analyze the circuits.
It is hard not to make contact with scope body when you have to make any knob adjustment.

[keeney123]

Re: I have never used an oscilloscope and don't know how they work

Forgot to upload file.

[budm]

Re: I have never used an oscilloscope and don't know how they work

I do not see the attachment, but using isolation transformer with floating HOT and NEUTRAL will be same as working in the cold side of the circuit since the primary side of the product you are working on are now isolated from the incoming AC.
You have to watch out as to what kind of isolation transformer you get, some will have Neutral bonded to the Ground, for example:
http://www.tripplite.com/product/Sta...ansformers/839

I had people telling me that the scope and the unit he was working on was still damaged when using this isolation transformer, I told him that it is not fully isolated transformer, he did not believe so he check the secondary winding and the incoming ground and sure enough the Neutral is bonded to Ground.
I do not float my test equipment, I float what I am working on when the primary side has active circuits that needs to be troubleshoot and with safety ground still present, or I use differential probe.
https://www.badcaps.net/forum/showpo...72&postcount=6
And for critical circuit, I use TOPAZ ULTRA iso Xformer with minimum leakage capacitance, very hard to come by, http://www.ebay.com/itm/like/171145692167?lpid=82
Just think of it when you make the measurement with scope or what ever in the cold side of the circuit, the switching transformer is THE ISOLATION TRANSFORMER.
If you can afford differential probes, that will be good thing to have.
And remember one thing, the ref Ground of the switching circuit in the primary side is not referenced to the incoming/safety ground, it is referenced to the negative leg of the main filter cap. When you work in the circuit, you will look to see how it is designed and how you go about making the measurement.
Circuit ground is not the same as safety ground and depend on the circuit sometime you can tie the circuit ground to the safety ground.

Page 2 of TEXTRONIX:
Floating An Oscilloscope: A
Definition
“Floating” a ground referenced oscilloscope
is the technique of defeating
the oscilloscope’s protective grounding
system – disconnecting “signal
common” from earth, either by defeating
the grounding system or using an
isolation transformer. This allows
accessible parts of the instrument
such as chassis, cabinet, and connectors
to assume the potential of the
probe ground lead connection point.
This is dangerous, not only from the
standpoint of elevated voltages present
on the oscilloscope (a shock hazard
to the operator), but also due to
cumulative stresses on the oscilloscope’s
power transformer insulation.
This stress may not cause immediate
failure, but may lead to future dangerous
failures (a shock and fire hazard),
even after returning the oscilloscope
to properly grounded operation!
Not only is floating a ground-referenced
oscilloscope dangerous, but
the measurements are often inaccurate.
This results from the total
capacitance of the oscilloscope chassis
being directly connected to the
circuit under test at the point where
the common lead is connected.

Bottom line: SAFETY, SAFETY, and SAFETY.
BTW, most of the electronics training hardly teaches about safety Ground and Circuit Ground, most people see the word Ground and think that they are the same, I see that so many times here when asking OP to take the Voltage readings in the Primary side.

[keeney123]

Re: I have never used an oscilloscope and don't know how they work

I think this is very useful for people who are learning or who are advance users of
Oscilloscopes.
" I had people telling me that the scope and the unit he was working on was still damaged when using this isolation transformer, I told him that it is not fully isolated transformer, he did not believe so he check the secondary winding and the incoming ground and sure enough the Neutral is bonded to Ground.
I do not float my test equipment, I float what I am working on when the primary side has active circuits that needs to be troubleshoot and with safety ground still present, or I use differential probe."
https://www.badcaps.net/forum/showpos...72&postcount=6
And BudM you are right about not learning this in school. I never learned this in 3.5 years of school nor did I learn it in 15 years as an electronic technician. Isolating the device one works on and not the test equipment is the way to go because the safety ground on the test equipment will protect the operator of any voltage that may make it's way to chassis on the test equipment. Thank you for your input it is of a great value and this is the perfect forum to express it. And I think that measuring the isolation transformers output resistance to ground and also, measuring the output voltage to ground are good procedures to follow. If one reads any resistance or voltage then that is not a isolation transformer, that is resistance less than what would create a potential harm. Any voltage measurement from a ground to either side of the output of the isolation transformer would make that a potential danger.

[orientalsniper]

Re: I have never used an oscilloscope and don't know how they work

HI

Just watch this. Here

Thank you! That helped much, I also appreciate what the others were saying too.