Grundig MO20 no Signal detected - Page 1
Forum section: electronics / testgear

author: tillewolle
author_rank: Contributor
timestamp: December 31, 2019, 12:53:01 am
content: 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?

author: Specmaster
author_rank: Super Contributor
timestamp: December 31, 2019, 01:18:11 am
content: 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.

author: tillewolle
author_rank: Contributor
timestamp: December 31, 2019, 10:48:06 am
content: Quote from: Specmaster on December 31, 2019, 01:18:11 amNothing:without X/Ywith 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.

author: Specmaster
author_rank: Super Contributor
timestamp: December 31, 2019, 01:06:17 pm
content: 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 youNext, 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)?

author: tillewolle
author_rank: Contributor
timestamp: January 02, 2020, 11:56:33 am
content: Quote from: Specmaster on December 31, 2019, 01:06:17 pmnice video! got it!Quote from: Specmaster on December 31, 2019, 01:06:17 pmYeah 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 digimesshttp://digimessinstruments.co.uk/manuals/english/moseriesengandger.pdfwhich seems to be similar but not identical.Quote from: Specmaster on December 31, 2019, 01:06:17 pmNo 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.Quote from: Specmaster on December 31, 2019, 01:06:17 pmCan you upload it, please?Quote from: Specmaster on December 31, 2019, 01:06:17 pmYeah the dot bounces around a bit. Not much.

author: Specmaster
author_rank: Super Contributor
timestamp: January 02, 2020, 12:32:00 pm
content: 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?

author: Specmaster
author_rank: Super Contributor
timestamp: January 02, 2020, 01:27:46 pm
content: 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.

author: tillewolle
author_rank: Contributor
timestamp: January 02, 2020, 02:21:36 pm
content: Quote from: Specmaster on January 02, 2020, 12:32:00 pmYeah 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.Quote from: Specmaster on January 02, 2020, 12:32:00 pmIt's a voltcraft VC-130-1... pretty basic low-end digital one

author: Specmaster
author_rank: Super Contributor
timestamp: January 02, 2020, 02:45:38 pm
content: Quote from: tillewolle on January 02, 2020, 02:21:36 pmWell, 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.

author: tillewolle
author_rank: Contributor
timestamp: January 02, 2020, 04:07:51 pm
content: Quote from: Specmaster on January 02, 2020, 02:45:38 pmIt wouldn't be worth, paid 10 bucks...Quote from: Specmaster on January 02, 2020, 02:45:38 pmGot the instructions and tried but I think I'm not sure how you mean this setup

author: Specmaster
author_rank: Super Contributor
timestamp: January 03, 2020, 03:02:01 am
content: Plug the black lead into the COM terminal of the meter and the red lead into the bottom right terminal markeddiode 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.

author: Specmaster
author_rank: Super Contributor
timestamp: January 03, 2020, 03:19:27 am
content: 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

author: tillewolle
author_rank: Contributor
timestamp: January 04, 2020, 12:18:04 pm
content: Quote from: Specmaster on January 03, 2020, 03:02:01 amSo far: workingQuote from: Specmaster on January 03, 2020, 03:02:01 amBeeping!Quote from: Specmaster on January 03, 2020, 03:02:01 amYou 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.Quote from: Specmaster on January 03, 2020, 03:02:01 amYep! beeping!Quote from: Specmaster on January 03, 2020, 03:02:01 amThat'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?Quote from: Specmaster on January 03, 2020, 03:02:01 amMaybe 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!Quote from: Specmaster on January 03, 2020, 03:19:27 amWill watch this NOW!

author: Specmaster
author_rank: Super Contributor
timestamp: January 04, 2020, 10:00:58 pm
content: 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??

author: tillewolle
author_rank: Contributor
timestamp: January 06, 2020, 12:54:50 pm
content: Quote from: Specmaster on January 04, 2020, 10:00:58 pmThis is the plug.Quote from: Specmaster on January 04, 2020, 10:00:58 pmJust 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.

author: Specmaster
author_rank: Super Contributor
timestamp: January 06, 2020, 01:28:35 pm
content: 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 cablehttps://www.toughleads.co.uk/pages/european-socketsYou are putting yourself at risk of getting shocked, maybe fatally by use a 2 pin plug.

author: tillewolle
author_rank: Contributor
timestamp: January 06, 2020, 07:16:06 pm
content: Quote from: Specmaster on January 06, 2020, 01:28:35 pmIt's the plug from oscilloscope to power strip. The power strip has a regular 3 pinned plug.Quote from: Specmaster on January 06, 2020, 01:28:35 pmThis is the way the oscilloscope came from factory. It's fixed and leads straight into the oscilloscope.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 06, 2020, 07:42:03 pm
content: Quote from: tillewolle on January 06, 2020, 07:16:06 pmReally?

author: Specmaster
author_rank: Super Contributor
timestamp: January 06, 2020, 08:24:37 pm
content: Quote from: tillewolle on January 06, 2020, 07:16:06 pmQuote from: Specmaster on January 06, 2020, 01:28:35 pmThis is the way the oscilloscope came from factory. It's fixed and leads straight into the oscilloscope.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

author: tillewolle
author_rank: Contributor
timestamp: January 07, 2020, 05:31:05 am
content: Quote from: PA0PBZ on January 06, 2020, 07:42:03 pmThis is how it looks like on the back. Maybe it's time to open up this thing?Quote from: Specmaster on January 06, 2020, 08:24:37 pmExactly. I was already wondering...

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 07, 2020, 07:55:29 am
content: The grommet is fine, but I have a strong feeling that the cord was replaced by a previous owner.

author: Specmaster
author_rank: Super Contributor
timestamp: January 07, 2020, 04:22:11 pm
content: Quote from: tillewolle on January 07, 2020, 05:31:05 amI 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.

author: tillewolle
author_rank: Contributor
timestamp: January 07, 2020, 05:27:35 pm
content: Quote from: Specmaster on January 07, 2020, 04:22:11 pmI 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.

author: Specmaster
author_rank: Super Contributor
timestamp: January 07, 2020, 06:57:58 pm
content: 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.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 07, 2020, 07:19:40 pm
content: 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

author: Messtechniker
author_rank: Frequent Contributor
timestamp: January 08, 2020, 06:10:21 am
content: If thus unit were to have double insulation you would findon a label or printed on the rear a smaller square withina larger square. See attachment.Thus, if not present, then the mains cord you have foundwas improperly replaced.

author: tillewolle
author_rank: Contributor
timestamp: January 08, 2020, 09:02:54 pm
content: Quote from: Specmaster on January 07, 2020, 06:57:58 pmDon't worry, I can see your pointI think it's because I try to describe everything as detailed as possible and I'm more firm with the German terms for all of this. So it's more a language barrier because I need to reread all things a lot of times to make sure I'm 100% safe and doing it rightQuote from: PA0PBZ on January 07, 2020, 07:19:40 pmYeah! It moves from middle to the right! Just when X/Y is pressed.Quote from: Messtechniker on January 08, 2020, 06:10:21 amYou mean like this?

author: Specmaster
author_rank: Super Contributor
timestamp: January 08, 2020, 09:46:40 pm
content: Yes that is the Double Insulated symbol so may be it is safe after all. I still have my doubts but without getting a full copy of a manual for it I can't be sure, it might be what /02 after the model number denotes?The case of the scope is made of metal, yes? If yes, grab your multimeter and set it up again for the continuity test and see if the outer part of the BNC socket is connected to the case. If yes, then I'd be extremely careful when using it because while you not in any danger of blowing the scope or the probes (as in the video of Dave's on EEV Blogg). You are then putting yourself in danger of electrocution because if you get the connections wrong on the reel to reel tape recorder, the case could be live (hot) and if you then touch the case and ground (earth) you will be shocked or worse.With the movement on the screen over the right, is this the dot moving to the right, or is it making a line? If it is making a line then rotate the control in the top line of knobs with double-headed arrow, to the left and see if it fills the screen. Study the attached photo and move the controls to the same settings as shown in the photo and connect a probe (if you have 2 probes connect both as shown) and see what happens to the screen then.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 09, 2020, 07:49:51 am
content: Quote from: Specmaster on January 08, 2020, 09:46:40 pmThat looks like a piece of paper that someone glued on, and by the looks of it it's ready to fall off.

author: tautech
author_rank: Super Contributor
timestamp: January 09, 2020, 08:25:51 am
content: Quote from: PA0PBZ on January 09, 2020, 07:49:51 amExactly, double insulated symbols are always screen printed on or embossed into the case.IMHO it's a mod.....beware !

author: Specmaster
author_rank: Super Contributor
timestamp: January 09, 2020, 08:44:06 am
content: Quote from: tautech on January 09, 2020, 08:25:51 amThats what I'm concerned about, if its a mod and been poorly carried out, its possible for the entire scope to become a lethal time bomb just waiting for the right conditions to strike.

author: tillewolle
author_rank: Contributor
timestamp: January 09, 2020, 06:51:07 pm
content: Quote from: Specmaster on January 08, 2020, 09:46:40 pmWould nice to get the right one, but where?Quote from: Specmaster on January 08, 2020, 09:46:40 pmYes!Quote from: Specmaster on January 08, 2020, 09:46:40 pmNo it's not. Even if I put both probes on case.Quote from: Specmaster on January 08, 2020, 09:46:40 pmIt's moving the dot for the right.Quote from: Specmaster on January 08, 2020, 09:46:40 pmIt moves the dot from middle to the right.Quote from: Specmaster on January 08, 2020, 09:46:40 pmlike the photoWith Intens down

author: Specmaster
author_rank: Super Contributor
timestamp: January 13, 2020, 09:42:43 am
content: Looking at these results, it is clear that your scope has neither any vertical or horizontal activity which is a real bad place to be and unless you're going to be incredibly lucky, is very likely to mean that it is way beyond economical repair.My gut reaction at this stage is to dump it and buy another that you are able to see working before you part with cash for it. The logic behind this is I do not believe this left the factory as a double insulated device, which means that someone has been inside and meddled with it and what you are seeing is the end result where they did things that screwed it up, had no idea how to fix it so sold it on pronto hoping that the next buyer would not know any better until it was too late.Why do I think it has been messed about with? Is simple to understand, if the double insulation was a factory option then why was the symbol printed on a paper label and stuck on, why was it not printed on like the rest of the information on the back of the scope?Without a genuine workshop manual on the scope to work from, you are batting blind, even down to what voltage is supposed to be where? I know that you said that you would leave the CRT high voltage area well alone, well it is not quite that simple, because sometimes there are areas of the PCB that are connected with the CRT but not the EHT, but voltages there can be in the realms of 2 to 4 times the line volts. Yes these areas should be shielded but not always so or the shielding may have been left off by the person doing the modifications, and poking around without that all important and elusive manual, you are poking in the dark.You may disagree with me, but thats my considered opinion with many years of experience and you already have, and I'm sorry but I have to say it, made some school boy errors, as most people on this forum would have walked away from that scope because the visual clues that are available, 2 pin plug and 2 core cable, paper stuck on label with the double insulated symbol and also of course, the fact it was not working as intended when you saw it.

author: Specmaster
author_rank: Super Contributor
timestamp: January 20, 2020, 10:41:29 pm
content: You might like to check out this video, it elaborates on the video that Dave did with actual demonstrations, including using an isolation transformer which while can be an improvement in safety, can still under the right (or I should say WRONG) circumstances still expose you great danger.

author: tillewolle
author_rank: Contributor
timestamp: January 22, 2020, 09:55:48 pm
content: Yeah, guess I'm keeping my eyes open for another one. Any recommendations to start?

author: Specmaster
author_rank: Super Contributor
timestamp: January 22, 2020, 10:04:04 pm
content: Anything should be OK around that bandwidth should be pretty good and cheap, but make sure its working before buying it this around. I would have thought either a Phillips or Hameg should be plenty full in your neck of the woods.

author: tillewolle
author_rank: Contributor
timestamp: February 24, 2020, 09:51:18 pm
content: Not giving up...Found someone selling the same model with the same Sticker on it, same cable... So mine seems not to be unique.https://www.ebay-kleinanzeigen.de/s-anzeige/grundig-elektronik-oszilloskop-mo22-2-20-mhz-2-kanal/1331890265-168-6214

author: Specmaster
author_rank: Super Contributor
timestamp: February 24, 2020, 10:13:03 pm
content: Quote from: tillewolle on February 24, 2020, 09:51:18 pmSo it would seem, but it is possible that the same person may have had a few of these, maybe a laboratory somewhere had them modified for a specific purpose etc? Without a proper manual for the scope it is still going to be a hard uphill battle for someone such as yourself with an admitted very limited knowledge. Hence why I said that it would be better to source another scope of similar bandwidth but working to begin with, they can be picked up if you look around for very little money. Once your knowledge level increases, especially if you manage to locate a full and proper manual for that scope, you could then use the new one as a tool to assist you repairing the other. It is always a good idea to have more than one scope as old ones do tend to break quite often being as they are going to be around 40 years old now.

author: MarcX
author_rank: Contributor
timestamp: August 17, 2021, 05:24:44 pm
content: Quote from: Specmaster on February 24, 2020, 10:13:03 pmNo this variant was available from Grundig too (Schutzklasse II), and is mentioned in the manual. But you should pay attention by measuring voltages with more than 50VAC over earth because the grounding is connected with the chassis.For all people with german language skills, their is a copy of the manual on the german mikrocontroller.net bulletin board. (Page 5, Chapter 4)https://www.mikrocontroller.net/attachment/360138/MO22_AN.pdfThere was also an option for Z-Modulation (INTENS-MOD). All Grundig MO20, MO22, MO30, MO32, CO30 and CO33 (CO = Branded for Conrad Electronics Store) and also the Siemens branded versions, Oscilloscopes can be equipped with this option by adding a BNC connector which is connected to X-Deflection PCB when i‘m remembering correctly. (AUFHELLSCHALTER, page 4)https://www.mikrocontroller.net/attachment/360139/MO22_SM.pdf