Please help - I don't know what to do! :( - Page 1
Forum section: electronics / beginners

author: Isabella90
author_rank: Newbie
timestamp: April 22, 2013, 03:58:58 pm
content: Hello! I'm new here and I hope to get some help from people who worked in the past with oscilloscopes.I'm having a few problems and I don't know where they come from: first of all with the spot - it starts moving alone by itself on horizontal. If I try to fix it on the middle of the screen it runs itself in left and right side without touching anything. Also the spot is shaking like it were possesed!!!!The second problem: sometimes when I activate the dual channel it shows me 4 lines on the screen, like I was activating the quad channel function!!The third problem: sometimes if I try to move from channel 1 to channel 2, it doesn't work. And sometimes is viceversa: when I move from 2 to 1 it doesn't work, it shows nothing on the screen!If it helps, I can make a video and show you exactly what are the problems! Please help me and tell me what can I check, from where could those problems come. I must say that the oscilloscope was working very good and suddenly from one day to another the problems appeared.The oscilloscope is a Kenwood with 4 channels!Thank you!

author: Unknown
author_rank: Unknown
timestamp: April 22, 2013, 04:12:50 pm
content: Yes, a Video would help... show each problem one-by-one, to help you to follow up on.

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 22, 2013, 06:29:47 pm
content: It looks like readingOscilloscope Basics 1.0would solve it...

author: Unknown
author_rank: Unknown
timestamp: April 22, 2013, 08:28:11 pm
content: In deed... but just to make sure, that their is or is not a fault ! Isabella90 might need a basic guide book.

author: amyk
author_rank: Super Contributor
timestamp: April 23, 2013, 06:42:29 am
content: Quote from: vlf3 on April 22, 2013, 08:28:11 pmAgreed.At least you should tell us what you were trying to measure with the 'scope...

author: Isabella90
author_rank: Newbie
timestamp: April 23, 2013, 07:46:02 am
content: I wasn't trying to measure anything. I turned it on and then I saw the problems that I told you about. I was going to try using the oscilloscope in an experiment as ecg, the circuit was ready and everything and when I turned it on I saw what's going on. The thing is that I haven't used the oscilloscope since then when I saw how many problems appeard suddenly over night. Very interesting is that those problems appear randomly, I tried to make a video yesterday to show you what's wrong and it worked ok since now, I don't know when the problems will appear again and if they gonna appear.It's not a problem of calibration, because I was using this oscilloscope without problem since a few days ago....and I never had those problems!

author: Unknown
author_rank: Unknown
timestamp: April 23, 2013, 12:50:55 pm
content: @ Isabella90...Seems like you have an intermittent fault, or a number of them ! however, it's possible their might be a simple answer; e.g. have a good look inside your scope,"with the mains supply removed".Where the scope has cables and interconnection plugs or PCB to sockets; first check the power supply connections on-route via the scope's other electronics boards, X Y and beam CRO base tube... then make sure these connections are in good contact with the PCB's or pin connectors, and are clean with no sign of oxidation or solder dry-joints.You could also power-up the scope, then by using an insulated tool(not a screw driver)lightly tap the PCB boards and connectors, or any solder tag-pins to see if the faults occur ?(placing a mirror in front of the scope, to see what happens while your working in a blind area, can be useful); this would be a starting point to resolve these problems your experiencing; their are much more advanced area's to investigate that will push your understanding of oscilloscopes, so do the basics first; hopefully interconnections might be the problem.Note: If the scope has been in storage for some time ?, and not housed at room temperature, it's quite common for equipment to start producing faults.

author: w2aew
author_rank: Super Contributor
timestamp: April 23, 2013, 06:22:52 pm
content: You may want to take a look at some of the videos from the "sticky" thread in this forum regarding Oscilloscope Basics:https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/

author: nelus008
author_rank: Newbie
timestamp: November 09, 2013, 08:48:31 pm
content: I also have an oscilloscope like this one and i have the same problem with it. Have you managed to fix it since your last post? I wait for your reply. thanks

author: c4757p
author_rank: Super Contributor
timestamp: November 09, 2013, 08:52:31 pm
content: You really, really should post more information. How about a picture of the panel?

author: Isabella90
author_rank: Newbie
timestamp: November 09, 2013, 09:01:57 pm
content: No, I didn't solved the problem, I don't know what's wrong with it, now I don't even see the lines on the screen, only a light in the corners of the screen, like the line is there but outside the screen. And no one came with a solution.... I think I'll make a video to show the problem.

author: Isabella90
author_rank: Newbie
timestamp: November 09, 2013, 10:05:50 pm
content: Quote from: c4757p on November 09, 2013, 08:52:31 pmQuote from: nelus008 on November 09, 2013, 08:48:31 pmOk, so here is the video:After I uploaded it I saw that I made a couple of mistakes: when it starts I shoul see one line (I forgot I'm on channel 1), not 2, and the point should appear on X-Y button, not on B DLY'D. So, I wait for opinions and solutions!

author: c4757p
author_rank: Super Contributor
timestamp: November 09, 2013, 10:11:49 pm
content: One half of your vertical deflection driver is almost certainly blown. Either a shorted transistor on one side or an open transistor on the other. The CRT has deflected all the way to the top. Get the schematics for the scope, study the vertical driver amplifier, and start probing transistors (a voltmeter should be sufficient) for bias points that are seriously far from where they should be. (You may need to find someone to help you with this, if you're not familiar enough with transistor circuits).Also, check the connections to the CRT, it could be as simple as one side of the deflection pins being loose.

author: Isabella90
author_rank: Newbie
timestamp: November 09, 2013, 10:21:14 pm
content: Quote from: c4757p on November 09, 2013, 10:11:49 pmI checked the connection to the CRT and it's OK. I have schematics but....as a beginner who learn without any help, I'm not quite sure what and where should I check. I can also attach the scheme if someone can tell me on what area to seek for problems because I have a vertical amplifier unit, another vertical preamplifier unit and also the vertical output to CRT. Or I should check all those units? Also I wonder, could the power source cause all those problems?Thank you very much!

author: nelus008
author_rank: Newbie
timestamp: November 09, 2013, 10:28:25 pm
content: Yes is it my problem too. Are there any test points to verify the vertical amplifier unit ?

author: nelus008
author_rank: Newbie
timestamp: November 09, 2013, 10:49:31 pm
content: For the ones who are interested here is the service manual for the oscilloscope :https://www.dropbox.com/s/tc49bsw1gfl4m1l/trio_kenwood_cs-2070_70mhz_oscilloscope.pdfI post it here because I found it very hard and I hope it will help in solving the problem.

author: Shock
author_rank: Super Contributor
timestamp: November 10, 2013, 09:30:27 am
content: What were you last doing on the scope before you noticed the problems occurring, were you measuring something? How long has it been working ok for?Please be aware of the lethal voltages in the CRT and Power Supply that both need to be discharged each time you need to safely work on the scope. As well as always having the scope disconnected from all power. If you aren't clear on this, or best safety practices don't work on it.One thing you could do is a visual inspection of boards 83, 84 as per the service manual and check for corrosion on the connectors, clean or at least reconnect them a few times being careful not to damage them. Check any damaged components, leaking caps and dry solder joints (especially around large resistors) while you are there. Always write down which ways you remove things so you avoid adding other issues.The service manual has some good troubleshooting flow charts with a block diagrams also. It has all the supply voltages to each connector on the board listed, which you can also check out with a multimeter (you may have to improvise some test leads). You to have knowledge of how to safely work on mains voltage equipment and were not to touch if you do this especially while powered up.

author: papo
author_rank: Regular Contributor
timestamp: November 10, 2013, 02:11:39 pm
content: Have a look at pages 102 and 103 of the manual (7-7 according to the original page numbering). There is a nice schematic of a relatively simple amplifier, I would start from there. Depending whether your measurements at the input are reasonable, work your way forward (towards the CRT, more likely) or backward (the preamp is described earlier in the manual).Have a look at the previous 2 pages for how to access the test points. And also consider page 90 for instructions on how to set up the scope and the test conditions.Lastly, please be very careful while probing in order not to damage the scope or yourself. The usual warnings related to probing running equipment apply, especially when it comes to high voltage CRT stuff.Good luck and I'm curious on how this works out

author: Isabella90
author_rank: Newbie
timestamp: November 10, 2013, 04:43:15 pm
content: Quote from: Shock on November 10, 2013, 09:30:27 amThe last time, when it worked very well, I was testing the output of an auto amplifier after I mounted it on the car. The oscilloscope was sitting on a metalic table and that table was outside on the ground. Could the problem come from there? After this measurement the oscilloscope started with the problems I first described when I opened the topic and ended up with what you see on video. The first problem was that it didn't wanted to change between channels anymore and now you see that the problem has got worst. I will try this week to identify problem according the advices I got now from you and I will keep in touch with news.Thank you again!

author: Shock
author_rank: Super Contributor
timestamp: November 11, 2013, 07:25:48 am
content: Table probably has nothing to do with it. But the fact you moved it, then it had problems does.Did it immediately show problems when powered up on the outside table?What did you use to power the scope, an extension cable or?Where exactly was it when you noticed the first problem. On your inside table?Was it dropped at all?It can help is narrowing it down. If it has been working fine for a long time it's not random (unless you take it inside and outside all the time).

author: John Coloccia
author_rank: Super Contributor
timestamp: November 12, 2013, 02:07:13 am
content: The first rule of debugging a suddenly failed circuit in the lab is to make a fist and bang on the table a few times. If that does nothing, nothing lost. If it suddenly works for a second, then at least you know you're just looking for a bad connection somewhere...and that happens more than you might think.

author: nelus008
author_rank: Newbie
timestamp: November 12, 2013, 04:03:44 am
content: Hi !Thank you guys for information i resolved my oscilloscop . My problem was bad connectin at vertical amplifier and preamplifier .Thank you again for sharing solutions!

author: Shock
author_rank: Super Contributor
timestamp: November 13, 2013, 03:34:15 am
content: Awesome one down.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: November 13, 2013, 11:18:49 am
content: Quote from: nelus008 on November 12, 2013, 04:03:44 amThats great!Any way you could post a pic of the target area to help the other person out?

author: Shock
author_rank: Super Contributor
timestamp: November 13, 2013, 04:15:48 pm
content: Both the boards are photographed in the service manual.