Grundig MO20 no Signal detected

[tillewolle]

Hey got a Grundig MO20 without probes and manual and now I'm trying to make it work. I ordered some probes at Amazon (AUTOUTLET P6100 100 MHz). Hope they're compatible but it seems that they work with common oscilloscopes.



Yeah, on this photo it says source CH2 but I tried all of them. Connected everything proper but I am not even getting a signal on the CRT. If I connect one probe it should at least give out a vertical line, right? I'm just seeing a dot in the middle. Both channels. Read about most oscilloscopes having a square wave generator. Mine seems also, right? The little thing that says 1Vpp with a square wave symbol. Also hooked up to this - just a dot.
Any ideas?

[Specmaster]

Ok, lets put the source switch back into Ch1 position, connect the probe to Ch1 input and the probe tip to the test point 1Vpp and press the X/Y button in the top left of the control panel and see what happens then.

Edit:-
I see that you're a newbie, be very careful when probing inside anything that is connected to the main supply or you could possible blow up your nice newly acquired scope so you might find this video of interest to you.

[tillewolle]

Ok, lets put the source switch back into Ch1 position, connect the probe to Ch1 input and the probe tip to the test point 1Vpp and press the X/Y button in the top left of the control panel and see what happens then.

Nothing:

without X/Y


with X/Y pressed.

What is this X/Y button doing?

Thank you for recommending Dave's video! It helped me a lot to prevent future disasters! To try out I redid the tasks in the beginning of the video:

Tested a power cord center earth pin (next to the oscilloscope) with both BNC-Connectors - nothing happens on the Multimeter.
Power cord earth pin to ground on probe - nothing on the multimeter.

[Specmaster]

First thing is the X/Y mode is a special mode that you more than likely will not use very often, this video explains it a bit more for you 

Next, I see in the photos that the small trace / dot does appear to move across the screen, is true? Have you tried to play around with any of the controls, like the Timebase control? Have you got your self a copy of the instruction manual for the scope at all?.

Are you sure that you used the multimeter correctly when you checked for earth reference continuity between the earth pin of the mains lead plug and the BNC outer shell? Did you get a connection working between the probe croc clip and the outer metal part of the BNC plug on the probe lead? I have never come across probe that did not have this connection.

I have downloaded a service manual for your scope and the BNC socket on the front panel is connected to the Earth ground connection.

Can you move the screen image up and down using the Ch1 and or Ch2 (which ever the probe is connected to and also the source switch must be moved to the same channel)?

[tillewolle]

First thing is the X/Y mode is a special mode that you more than likely will not use very often, this video explains it a bit more for you

nice video! got it!

Next, I see in the photos that the small trace / dot does appear to move across the screen, is true? Have you tried to play around with any of the controls, like the Timebase control? Have you got your self a copy of the instruction manual for the scope at all?.

Yeah right! It moves a bit to the right! With X/Y pressed, I'm able to shift it with the <--> knob at the time base section. I do have a manual for the MO Series by digimess http://digimessinstruments.co.uk/manuals/english/moseriesengandger.pdf which seems to be similar but not identical.

Are you sure that you used the multimeter correctly when you checked for earth reference continuity between the earth pin of the mains lead plug and the BNC outer shell? Did you get a connection working between the probe croc clip and the outer metal part of the BNC plug on the probe lead? I have never come across probe that did not have this connection.

No I'm absolutely not. I'm kind of a newbie... just the basics. Just rewatched how Dave did and tada: I get some values around 180ish but it seems like a pulse. tried connecting the probe croc with outer metal BNC and yeah it gets around 30 and then drops down to 0.

I have downloaded a service manual for your scope and the BNC socket on the front panel is connected to the Earth ground connection.

Can you upload it, please?

Can you move the screen image up and down using the Ch1 and or Ch2 (which ever the probe is connected to and also the source switch must be moved to the same channel)?

Yeah the dot bounces around a bit. Not much.

[Specmaster]

OK, I see.

1st. I take it then that you have just brought this Grundig scope? Was it sold to you as working OK or was it sold as spares / repair? If it was sold as working, I'd send it back and complain because it clearly is not working and requires some serious work on it get it working.

2nd Did you buy the scope on eBay?

3rd, What type of meter do you have, analogue or Digital and what model is it?

[Specmaster]

As a newbie, you might find this series of videos on how to use a scope very useful. Click on the subscribe button and then click on the Bell icon and you will be able to see all the other videos in the series and also get notified every time there is a new one added.

[tillewolle]

OK, I see.

1st. I take it then that you have just brought this Grundig scope? Was it sold to you as working OK or was it sold as spares / repair? If it was sold as working, I'd send it back and complain because it clearly is not working and requires some serious work on it get it working.

Yeah got it craigslist style. The guy said he never used it because he had no probes. It was given away to workers of a energy supplier when they switched from analog to digital in their labs.

3rd, What type of meter do you have, analogue or Digital and what model is it?

It's a voltcraft VC-130-1... pretty basic low-end digital one

[Specmaster]

OK, I see.

1st. I take it then that you have just brought this Grundig scope? Was it sold to you as working OK or was it sold as spares / repair? If it was sold as working, I'd send it back and complain because it clearly is not working and requires some serious work on it get it working.

Yeah got it craigslist style. The guy said he never used it because he had no probes. It was given away to workers of a energy supplier when they switched from analog to digital in their labs.

3rd, What type of meter do you have, analogue or Digital and what model is it?

It's a voltcraft VC-130-1... pretty basic low-end digital one

Well, there's lesson number 1, especially for a newbie, always look for ones that are clearly visible as working, either by way of demonstration or photos in the listing showing it working and also a listing that states it is working. That way, if it is not working you can get your money back, especially if you use eBay to do your buying on and also use PayPal for the payment method. I don't know anything about your Craigslist, or even if it has any buyer protection.

I think that this is the set of instructions for your meter, if so, then use the audible continuity checker mode to check if your bnc sockets are connected to the chassis and to mains earth pin on the mains input socket. If you get a buzz then they are mains referenced which is what they should be. Oh, I doubt I need to tell you this, but just in case, do not do this while plugged into the wall outlet, plug out first.

[tillewolle]

Well, there's lesson number 1, especially for a newbie, always look for ones that are clearly visible as working, either by way of demonstration or photos in the listing showing it working and also a listing that states it is working. That way, if it is not working you can get your money back, especially if you use eBay to do your buying on and also use PayPal for the payment method. I don't know anything about your Craigslist, or even if it has any buyer protection.

It wouldn't be worth, paid 10 bucks...

I think that this is the set of instructions for your meter, if so, then use the audible continuity checker mode to check if your bnc sockets are connected to the chassis and to mains earth pin on the mains input socket. If you get a buzz then they are mains referenced which is what they should be. Oh, I doubt I need to tell you this, but just in case, do not do this while plugged into the wall outlet, plug out first.

Got the instructions and tried but I think I'm not sure how you mean this setup

[Specmaster]

Plug the black lead into the COM terminal of the meter and the red lead into the bottom right terminal marked  diode and mA, rotate the selector switch to the diode and audio setting on the left side of the meter (between the 200 and 10 positions) and then press the power button. Though the probe tips together and you should hear a beep, this is the continuity mode and is used to check connections that are common, in this case we are talking about the BNC sockets on the front of your scope, put a probe onto the outer shell of the BNC sockets and again you should get a beep when doing this, that means that they are connected together. Next unplug the power cable from the mains socket on your wall or bench socket or where ever you plug it in to get power to the scope. Leave the IDC (kettle plug end) plugged into the scope, connect one meter probe to a BNC outer shell and the other probe to the earth pin of the power cable plug and again you should hear a beep from the meter, that proves that the mains earth is connected through to the BNC sockets.

Grab your scope probes and connect a meter probe to the little cable with a croc clip of the end, and connect the other probe to the BNC plug outer (metal on the outside) and again you should hear a beep from the meter, this then proves that the probes and the scope are ground / earth referenced as Dave referred to in his video and hence the need for extreme caution when using the probes on mains connected or ground referenced equipment.

With regard to the scope, if you are still unable to get it working with the aid of the information I sent you, consider getting rid of it and buying another one that can seen working.

I don't mean this dis respectively, but I do wonder if you are actually ready for scope yet, you would perhaps be better off learning to use your multimeter to best advantage, there are lots of members on the forum who don't have a scope to their name, it is not a must-have item. A meter is, a soldering iron and some hand tools are the basic tool kit you require to start experimenting with and build up your tool kit to other things like scopes, function generators, signal generator, LCR meter etc as your skills grow.

There are also a number of electronics courses on line that you could subscribe to, in order start to learn about electronics and hone your skills.     

[Specmaster]

Here is another group of videos that help explain how to use certain equipment etc. As before click subscribe and and the bell icon/

https://www.google.com/search?client=firefox-b-d&q=Basic+use+of+a+multmeter#kpvalbx=_yq4OXoalAcbGgQbHypqwDg33

[tillewolle]

Plug the black lead into the COM terminal of the meter and the red lead into the bottom right terminal marked  diode and mA, rotate the selector switch to the diode and audio setting on the left side of the meter (between the 200 and 10 positions) and then press the power button. Though the probe tips together and you should hear a beep, this is the continuity mode and is used to check connections that are common

So far: working

, in this case we are talking about the BNC sockets on the front of your scope, put a probe onto the outer shell of the BNC sockets and again you should get a beep when doing this, that means that they are connected together.

Beeping!

Next unplug the power cable from the mains socket on your wall or bench socket or where ever you plug it in to get power to the scope. Leave the IDC (kettle plug end) plugged into the scope, connect one meter probe to a BNC outer shell and the other probe to the earth pin of the power cable plug and again you should hear a beep from the meter, that proves that the mains earth is connected through to the BNC sockets.

You mean the end of the power plug? Wiki gives me a "C15/C16 coupler" - never heard kettle plug before - English isn't my native language. The cable of the oscilloscope on one end is a EN 50075 Europlug with no earth pin (as far as I understood the concept of plugs in the last weeks.) The other part of the cable is fixed to the oscilloscope.

When I test the earth pin from my power strip with the outer BNC shell I don't hear a beep.

Grab your scope probes and connect a meter probe to the little cable with a croc clip of the end, and connect the other probe to the BNC plug outer (metal on the outside) and again you should hear a beep from the meter, this then proves that the probes and the scope are ground / earth referenced as Dave referred to in his video and hence the need for extreme caution when using the probes on mains connected or ground referenced equipment.

Yep! beeping!

With regard to the scope, if you are still unable to get it working with the aid of the information I sent you, consider getting rid of it and buying another one that can seen working.

I don't mean this dis respectively, but I do wonder if you are actually ready for scope yet, you would perhaps be better off learning to use your multimeter to best advantage, there are lots of members on the forum who don't have a scope to their name, it is not a must-have item. A meter is, a soldering iron and some hand tools are the basic tool kit you require to start experimenting with and build up your tool kit to other things like scopes, function generators, signal generator, LCR meter etc as your skills grow.

That's the best part of the process of learning, right? Troubleshooting, troubleshooting, troubleshooting. Asking questions in forums, watching videos on YouTube 10x and trying to understand how all this black magic works. Otherwise I wouldn't even have a idea about all that. You already helped me a lot! These are not my first steps in electronics. Usually I start something, fail and start it again 2 months later with a lot more knowledge. The oscilloscope came in very handy so why not try it?

There are also a number of electronics courses on line that you could subscribe to, in order start to learn about electronics and hone your skills.

Maybe that's the problem: Where to start? What is more important? When do I have the motivation to think about exactly this problem? With a concrete project it's waaaaaay more fun!

Here is another group of videos that help explain how to use certain equipment etc. As before click subscribe and and the bell icon/

https://www.google.com/search?client=firefox-b-d&q=Basic+use+of+a+multmeter#kpvalbx=_yq4OXoalAcbGgQbHypqwDg33

Will watch this NOW!

[Specmaster]

Take a photo of the Euro plug that you have, I'm not understanding which one you mean. When you say power strip earth pin, is your scope actually plugged into the power strip??

[tillewolle]

Take a photo of the Euro plug that you have, I'm not understanding which one you mean.

This is the plug.

When you say power strip earth pin, is your scope actually plugged into the power strip??

Just checked it again - yes, scope is plugged into the power strip. Measured it again. Earth Pin of power strip and BNC-Connector shell (tested both channels!) - No beep.

[Specmaster]

Where is this euro 2 pin plug fitted, is on the power strip or the scope power lead?. Either way it is the wrong plug, it only connects to Live and Neutral, there are 3 pin plugs , or 2 pin plugs with scrapping earth connections on the side.  This link shows the type of plug that need to power the scope with in must 3 core cable https://www.toughleads.co.uk/pages/european-sockets You are putting yourself at risk of getting shocked, maybe fatally by use a 2 pin plug.

[tillewolle]

Where is this euro 2 pin plug fitted, is on the power strip or the scope power lead?

It's the plug from oscilloscope to power strip. The power strip has a regular 3 pinned plug.[/quote]

Either way it is the wrong plug, it only connects to Live and Neutral, there are 3 pin plugs , or 2 pin plugs with scrapping earth connections on the side.  This link shows the type of plug that need to power the scope with in must 3 core cable https://www.toughleads.co.uk/pages/european-sockets You are putting yourself at risk of getting shocked, maybe fatally by use a 2 pin plug.

This is the way the oscilloscope came from factory. It's fixed and leads straight into the oscilloscope.

[PA0PBZ]

This is the way the oscilloscope came from factory. It's fixed and leads straight into the oscilloscope.

Really?

[Specmaster]

Where is this euro 2 pin plug fitted, is on the power strip or the scope power lead?

It's the plug from oscilloscope to power strip. The power strip has a regular 3 pinned plug.

Either way it is the wrong plug, it only connects to Live and Neutral, there are 3 pin plugs , or 2 pin plugs with scrapping earth connections on the side.  This link shows the type of plug that need to power the scope with in must 3 core cable https://www.toughleads.co.uk/pages/european-sockets You are putting yourself at risk of getting shocked, maybe fatally by use a 2 pin plug.

This is the way the oscilloscope came from factory. It's fixed and leads straight into the oscilloscope.
[/quote]

So the power cable enters the oscilloscope via a grommet then? I find that somewhat odd, I seriously doubt it was supplied like that from the factory. I'm pretty sure it should have a lead like this one

[tillewolle]

Really?

 This is how it looks like on the back. Maybe it's time to open up this thing?

So the power cable enters the oscilloscope via a grommet then? I find that somewhat odd, I seriously doubt it was supplied like that from the factory. I'm pretty sure it should have a lead like this one

Exactly. I was already wondering...

[PA0PBZ]

The grommet is fine, but I have a strong feeling that the cord was replaced by a previous owner.

[Specmaster]

Really?

(Attachment Link)

 This is how it looks like on the back. Maybe it's time to open up this thing?

So the power cable enters the oscilloscope via a grommet then? I find that somewhat odd, I seriously doubt it was supplied like that from the factory. I'm pretty sure it should have a lead like this one

Exactly. I was already wondering...

I think its as PA0PBZ says, a previous owner has replaced the 3 core cord with 2 core, perhaps in an attempt to remove the earth reference for safety, which sadly opens up another even bigger issue in my view, unless that particular model of scope is double insulated, which I seriously doubt, and that is the possibility of its case becoming not only live, but live at a far higher potential, maybe even in the kV range. Also I really don't think that a scope with it all of its many dangers, is the type of project for a newbie to take on especially given that you aren't even fully aware yet how to full use of your digital multimeter. Scopes often have voltages on some power rails in the 100's of volts and on the CRT, in kilovolts. There are so many traps for young inexperienced players, that I would consider leaving the scope alone until I had gained much more experience in not just electronics, but also in repairs in general of equipment. If you feel that you must have a scope, then consider the purchase of a known working one. 

[tillewolle]

I think its as PA0PBZ says, a previous owner has replaced the 3 core cord with 2 core, perhaps in an attempt to remove the earth reference for safety, which sadly opens up another even bigger issue in my view, unless that particular model of scope is double insulated, which I seriously doubt, and that is the possibility of its case becoming not only live, but live at a far higher potential, maybe even in the kV range. Also I really don't think that a scope with it all of its many dangers, is the type of project for a newbie to take on especially given that you aren't even fully aware yet how to full use of your digital multimeter. Scopes often have voltages on some power rails in the 100's of volts and on the CRT, in kilovolts. There are so many traps for young inexperienced players, that I would consider leaving the scope alone until I had gained much more experience in not just electronics, but also in repairs in general of equipment. If you feel that you must have a scope, then consider the purchase of a known working one.

I just want to open it, to see, where the cable is going and how it's mounted. Without power plugged in and of course I won't open or even touch the CRT region.
Those aren't my first experiments with electronics. I am repairing and playing with electronics for a few years now. Before I try something I don't know yet, I do inform myself. Eg: I registered and posted to this board to NOT harm myself or someone else. I just want to understand how all this exactly works and following eevblog on yt for around a year made me very courious and of course careful. My last project was repairing a completely broken Tascam TSR-8 tape reel. I finished it, it runs almost perfectly now but I need an oscilloscope to calibrate it.

[Specmaster]

Oh I see, I thought that judging from your comments especially to the test meter issues that you was more of a newbie then you actually are, sorry.

[PA0PBZ]

If you turn the timebase knob fully counterclockwise can you see a moving dot instead of a line? Try both positions of the X/Y button. I have a feeling that the thing is broken, maybe just a loose wire inside, maybe worse. If you are ever in the neighborhood of Amsterdam bring your scope and we will fix it