Of course you do, everyone has a DMM and a soldering iron !

The recall of Tek TDS200 series was to correct a too thin PCB trace that acted as a fuse if a ground loop was made so that if the trace blew/vaporized the input BNC's were no longer mains ground referenced therefore use of the scope in such a state could present a shock hazard to the user.
PCB's were replaced for the increased load arising from a ground loop so to blow or trip a fuse/breaker and not fuse the trace.
With a soldering iron you can easily do the mod yourself just by adding a cable of say 1-1.5mm2 from the power inlet mains earth to the PCB ground plane near the input BNC's.

If the connection is already open between mains ground and input BNC's it needs fixing anyways, but this is where you need the DMM for the continuity check.

Thanks a lot for the info, I checked continuity with ground and there was, but I'm not sure if that could got blown up by the lil spark I saw... Would really like to understand why that happened better... I think it was the parasitic capacitance charging but im not sure

 

Thanks a lot for the info, I checked continuity with ground and there was, but I'm not sure if that could got blown up by the lil spark I saw... Would really like to understand why that happened better... I think it was the parasitic capacitance charging but im not sure

Please describe exactly how you tested the ground to BNC connection ? Exactly in every detail.

 

Please describe exactly how you tested the ground to BNC connection ? Exactly in every detail.

I got the multimeter on continuity mode, I put one lead in the metal frame of my mains sockets (where i plug devices), and the other one in the BNC ground, DMM starts beeping, and ohm reading is low <1ohm

 

I got the multimeter on continuity mode, I put one lead in the metal frame of my mains sockets (where i plug devices), and the other one in the BNC ground, DMM starts beeping, and ohm reading is low <1ohm

While the scope was plugged in ?
Please recheck with the scope unplugged for continuity between the mains lead earth pin and the BNC's, all of them please.

 

While the scope was plugged in ?
Please recheck with the scope unplugged for continuity between the mains lead earth pin and the BNC's, all of them please.

Yes, thanks a lot! Should I open another thread to discuss about this? I guess the question of the title got solved, so it's starting to go a bit offtopic I guess :/

 

Yes, thanks a lot! Should I open another thread to discuss about this? I guess the question of the title got solved, so it's starting to go a bit offtopic I guess :/

Why ? If you have proved continuity from all BNC's to mains ground then the scope is perfectly safe to use which was something you doubted a while back.
Note, Tek didn't make a very robust build of the BNC's and how they connect to the mainboard in TDS200 so be careful with the BNC's for them not to suffer any physical stress that might break their mounting onto the mainboard.
It's a common fault in these old DSO's and one Tek never repeated and instead either used 4 pin BNC sockets or used threaded bulkhead versions and a steel plate chassis.
They're a just fine and basic DSO however now aging and with a few faults that if you know about you can protect against.

Enjoy your visions into the world of waveforms !

 

Why ? If you have proved continuity from all BNC's to mains ground then the scope is perfectly safe to use which was something you doubted a while back.
Note, Tek didn't make a very robust build of the BNC's and how they connect to the mainboard in TDS200 so be careful with the BNC's for them not to suffer any physical stress that might break their mounting onto the mainboard.
It's a common fault in these old DSO's and one Tek never repeated and instead either used 4 pin BNC sockets or used threaded bulkhead versions and a steel plate chassis.
They're a just fine and basic DSO however now aging and with a few faults that if you know about you can protect against.

Enjoy your visions into the world of waveforms !

I've just rechecked what you told me, and I'm getting readings of 5ohm or less everytime, so I guess all connectors are OK

I've talked to the guy who sold me the equipment about the problem, to see if he could do the fix. He does not seemreally worried about it, he told me it's better if I blow a trace than a probe, and that some measures have to be made without earth to be able to do differential measurements, I guess he's right on that.

He also told me that the GFCI should also protect me before the trace is blown (all houses have 30mA GFCI max here, but as long as I know it's already enough to kill me if it doesn't trip fast enough)

For the moment, my idea was to use a DC isolated supply, but, from what I'm seeing, maybe it's better to just stick to ground referenced measurements and avoid connecting ground to the negative isolated output... First time I did it I saw a little spark and still can't say which was the reason of that... I'm supposing it's the capacitance between GND and negative being charged, but I would really like to confirm it.

[EDIT] I did some measurements from gnd to negative and positive channels, oh god, having a "good" scope is a new world XD I could actually see that negative is -7V below GND and positive is 7V above GND, and, they suffer from some syncronyzed AC ripple, I guess this might be associated with the voltage drop on the wires coming to the outlet, I might check if by disconnecting more items, the ripple goes down...

I was mostly concerned about blowing the scope when referencing negative to GND due to the spark, but now I understand that this was due to the capacitance charged to 7V between my scope and the negative and positive outputs... I insert scope picture

Thanks a lot for the help

 

You now need more help.
You have made an error in how you have set the channel inputs.

See how the display shows a 2V/Div setting yet measurements say 7V ?
I’ll let you learn how to set the probes and inputs correctly.

Also learn that when you compensate probes you’e connected to a reference signal that also serves as a sanity check.

 

Next to the probe jacks is a standard square wave signal used for probe compensation. That will give you a 1KHz 5V square wave for compensating your 10x probes and also a solid and trusted signal for checking operation.

 

You now need more help.
You have made an error in how you have set the channel inputs.

See how the display shows a 2V/Div setting yet measurements say 7V ?
I’ll let you learn how to set the probes and inputs correctly.

Also learn that when you compensate probes you’e connected to a reference signal that also serves as a sanity check.

Yes, I see!! the measurements are correct, it's 7V Rms, since the output of the DC power supply is set to 14V, each output (positive or negative) shows +-7V DC respectly, with the synchronized ripple, so that if you rest ch2-ch1 the result is 14 (ch2 is conencted to positive 14V of the psu and ch1 is connected to negative output) if I tie negative to ground via a 10kohm resistor, negative drops to 0v and positive stays at 14, the ripple also dissapears...

Next to the probe jacks is a standard square wave signal used for probe compensation. That will give you a 1KHz 5V square wave for compensating your 10x probes and also a solid and trusted signal for checking operation.

Thanks, I will have to do the calibration when I find a small enough screwdriver ^^'

 

Yes, I see!! the measurements are correct, it's 7V Rms, since the output of the DC power supply is set to 14V, each output (positive or negative) shows +-7V DC respectly, with the synchronized ripple, so that if you rest ch2-ch1 the result is 14 (ch2 is conencted to positive 14V of the psu and ch1 is connected to negative output) if I tie negative to ground via a 10kohm resistor, negative drops to 0v and positive stays at 14, the ripple also dissapears...

Thanks, I will have to do the calibration when I find a small enough screwdriver ^^'

Yes that too, that is probes must be properly compensated in 10x mode for measurements to be correct however this is NOT what I'm drawing your attention to.
IIRC even in these old Tek DSO's you can setup the correct probe attenuation in the channel menu.
Then the waveform amplitude matches the V/div setting rather than the mess you show now, a 7 V measurement and a waveform less than the 2V/div vertical setting on the scope.
You're using switchable probes right ? Have that setting match the channel setting.

 

Most waveform generators do not reach the power supply voltages.
7V RMS is 19.8V peak-to-peak that is shown on an oscilloscope.
7V peak is 14V peak-to- peak as shown on an oscilloscope that is 4.95V RMS.

 

Yes that too, that is probes must be properly compensated in 10x mode for measurements to be correct however this is NOT what I'm drawing your attention to.
IIRC even in these old Tek DSO's you can setup the correct probe attenuation in the channel menu.
Then the waveform amplitude matches the V/div setting rather than the mess you show now, a 7 V measurement and a waveform less than the 2V/div vertical setting on the scope.
You're using switchable probes right ? Have that setting match the channel setting.

Hello, the probes are correctly set, the only thing is that when you are measuring an AC signal with some DC offset, the reading should be done for Vmean and Vpeaktopeak, here i show Vrms and Vmean, so if you have some, the DC component of the waveform will be added to the RMS value calculation.

The waveform on channel 2, is the one UP, so it has 7VDC + 1VAC ripple @50Hz
The waveform on channel 1, is the one DOWN, so it has -7VDC + 1VAC ripple @50Hz

The readings are correct, maybe the waveform is distorted as the probes are not calibrated.

 

Welcome to the TDS 210.
What you have is a very good oscilloscope.
What you need to do know is to learn how to set up the TDS 210 and probes and how to use it properly. This is way more advanced than the oscilloscope you used before.

The first step is to adjust the scope probes.
Do you know how to do that?

 

The readings are correct, maybe the waveform is distorted as the probes are not calibrated.

This may seem a nitpick but the term is compensated not calibrated which is a very different thing. The reason 10x probes need compensation is at lower frequencies the voltage divider made up of R₁ and R₂ in the figure, which determines the scaling (in this case 10:1) and allows the probe to present very little loading to the circuit under test.

But, at higher frequencies the inherent capacitance of the probe creates the loading and Cprobe, which is made of parasitic capacitance of the probe and lead, works with C₂ to determine the loading. C₁ is the variable capacitor in the probe. It allows for adjustment of the capacitance of the probe to match the impedance of the scope input to cancel the capacitive reactance of the combination and compensate for this capacitive reaction at those higher frewquencies.

source: https://blog.poscope.com/oscilloscope-probe-compensation/
​

A side note is that the signal provided on the scope’s front panel is called the calibrator because it provides a standard for voltage and frequency.

Calibration is different from compensation in that it is about ensuring the scope’s display of values for a given signal presented at the probe input connector matches reality while compensation ensures that the presented signal isn’t distorted by parasitics.

 

If your probes have 1x and 10x settings you will always set it to 10x.
I will explain this later.

 

This may seem a nitpick but the term is compensated not calibrated which is a very different thing. The reason 10x probes need compensation is at lower frequencies the voltage divider made up of R₁ and R₂ in the figure, which determines the scaling (in this case 10:1) and allows the probe to present very little loading to the circuit under test.

But, at higher frequencies the inherent capacitance of the probe creates the loading and Cprobe, which is made of parasitic capacitance of the probe and lead, works with C₂ to determine the loading. C₁ is the variable capacitor in the probe. It allows for adjustment of the capacitance of the probe to match the impedance of the scope input to cancel the capacitive reactance of the combination and compensate for this capacitive reaction at those higher frewquencies.

View attachment 271419
source: https://blog.poscope.com/oscilloscope-probe-compensation/
​

A side note is that the signal provided on the scope’s front panel is called the calibrator because it provides a standard for voltage and frequency.

Calibration is different from compensation in that it is about ensuring the scope’s display of values for a given signal presented at the probe input connector matches reality while compensation ensures that the presented signal isn’t distorted by parasitics.

Thanks a lot, for the deep explanation, I need to get a good insight onto impedance matching to understand it better...
I have some doubts about if I can do differential measurements by powering the amps via an isolated power supply (i think mine is) but I see that if I want to measure ac signals some current might leak because of this capacitances...

 

If your probes have 1x and 10x settings you will always set it to 10x.
I will explain this later.

¿Then I should use fine adjustment on the scope? I see that with 1x I can get only upto 5V scale, with 10x I can go higher, and have better bandwidth, but the controls get quite coarse :/

 

Thanks a lot, for the deep explanation, I need to get a good insight onto impedance matching to understand it better...
I have some doubts about if I can do differential measurements by powering the amps via an isolated power supply (i think mine is) but I see that if I want to measure ac signals some current might leak because of this capacitances...

You are a bit confused with the function of resistors and capacitors.
Let’s take one step at a time.
Let’s get those probes set up first.

 

You are a bit confused with the function of resistors and capacitors.
Let’s take one step at a time.
Let’s get those probes set up first.

I'm not at home now, I'll tell you when I'm able to do it, shouldn't be difficult. First I am quite concerned about the safety recall and want to fix that.