Kikusui scope... no trace except on x/y mode. - Page 1
Forum section: electronics / testgear

author: 1jonnyz
author_rank: Contributor
timestamp: January 30, 2014, 07:42:51 pm
content: I just got a Kikusui COS6100M off of Ebay today. The mailman came up to my house carrying a big yellow bag, and yes my scope was in there with a packing label taped to it! No packing, no box, no nothing!! At any rate, I fired it up and the only way I get a trace is with the x/y button pushed in. Anyone have any idea what the problem may be? BTW, yes I am trying to get my money back, $70.00, but this thing really is clean! I would like to keep it if it is an easy fix, although it is a scope so there is no easy fix is there:)?Jon

author: grumpydoc
author_rank: Super Contributor
timestamp: January 30, 2014, 08:03:38 pm
content: Do you have enough experience with 'scopes to set it up to get a trace?The manual, if you haven't already found it is herehttp://www.kikusui.co.jp/kiku_manuals/C/COS6100M_E.PDFSet Horizontal mode=CH1, DISPLAY=A, Vertical mode=Auto, CH1 vertical sens to 1V/div, timebase to 1ms/div and the CH1 vertical position to mid rotation and internal trigger. Do you get a trace?If not push the beam find and what happens then.

author: 1jonnyz
author_rank: Contributor
timestamp: January 30, 2014, 08:29:20 pm
content: I don't have a whole lot of experience but I do have the manual, set it up per the manual, and get no trace when I hit beam finder. I get it on no channel, only x/y which shows 2 traces and they move to the right a bit when I hit beam finder.

author: grumpydoc
author_rank: Super Contributor
timestamp: January 30, 2014, 08:38:12 pm
content: QuoteX-Y shouldn't show any trace with no input just a dot (keep the intensity down to avoid burning the CRT) which you should be able to move with the position controls.A clear, decent resolution, photo (or photos - one in X-Y mode and one in "normal" mode) might help spot whether you just have it set up incorrectly.However I'd expect the beam finder to show something if you have a sweep but it's just off screen so it's starting to sound more like it is faulty.

author: 1jonnyz
author_rank: Contributor
timestamp: January 30, 2014, 09:29:12 pm
content: Here are some pics... the first I have the x/y in with the probe hooked to nothing, the second it is hooked to the 1V test, and the third just to show my settings. I get nothing at all with x/y not pushed in. I can move the trace up and down but it will not move sideways. I definitely think it is something internally wrong, it turns out I got it for free so it's all good:)!

author: grumpydoc
author_rank: Super Contributor
timestamp: January 30, 2014, 09:43:47 pm
content: Oh, OK - X-Y mode is behaving as expected, which means the CRT is OK as is the HV so it's possibly fixable.You're not getting a sweep - can't see anything obviously wrong with the settings although you can't see all of the positions of the knobs.Is the green "triggered" led lit when you have the probe test signal connected?Probably worth opening it up an checking for obvious internal damage/loose connections. As you're not very experienced do this with the 'scope off and disconnected from the mains (and having been so for a good few minutes). 'Scopes have lethal voltages present when powered up.What other test equipment do you have or can you access?

author: iDevice
author_rank: Regular Contributor
timestamp: January 30, 2014, 09:58:27 pm
content: Horizontal amp seems to be working, it is strange that you can't move the trace then.Did you try vertical amp the same way, and do you then get two vertical dots this time ? (you have to connect the probe to ch2, which is Y in X-Y mode)If this works then the problem is probably only around TB.By looking at the picture you are in auto mode so you should have a trace whether the sync section is working or not.Next step is first to check all power rails, then troubleshoot the TB with service manual.

author: 1jonnyz
author_rank: Contributor
timestamp: January 30, 2014, 10:09:32 pm
content: The trigger LED flicks on briefly when I push in the different channel buttons but the only time it stays on is x/y mode. I have a Tek 422 scope that works, an RCA VTVM, and a Fluke 27FM multimeter, so I have a few things here to track down the problem.iDevice, I just plugged into channel 2 and I do have 2 vertical dots and I can move them up and down but they will not move horizontally. I also don't have the service manual or schematic, only the users manual that I found online. This thing is really clean and it has a really sharp trace, I have to get this thing straightened out! Thanks for everyone's help btw!!Jon

author: iDevice
author_rank: Regular Contributor
timestamp: January 30, 2014, 10:46:18 pm
content: Quote from: 1jonnyz on January 30, 2014, 10:09:32 pmOk, good news, that means that both CH1 and CH2 are kind of working.When you say that you cannot move horizontally, which button do you use ?I mention this because, depending on the scope, horizontal position can be either the actual horizontal position knob or the CH1 position knob. This has to do with the way x-y mode is implemented.For instance, my Rigol DS4024 uses the vertical channel position knob used for X while my Tek 2247 uses the standard H pos knob.

author: sync
author_rank: Frequent Contributor
timestamp: January 30, 2014, 11:03:45 pm
content: The COS6100 (w/o M) manual contains schematics. I think the 6100M is very similar.http://www.kikusui.co.jp/kiku_manuals/C/COS6100_E.PDF

author: 1jonnyz
author_rank: Contributor
timestamp: January 31, 2014, 12:52:55 am
content: iDevice, I am using the position knob just below the time/div knob. Tomorrow I will take this apart and see if anything is visually wrong and go from there.Thanks for the manual sync, that is just what I needed as the manual for the 6100M doesn't have the parts list or schematics!

author: 1jonnyz
author_rank: Contributor
timestamp: January 31, 2014, 05:40:20 pm
content: I messed with this for awhile this morning, I found a cover off of channel 4 position switch off of the back that was floating around inside somewhere. I fired it up and I still can only get a trace on x/y mode. It does measure correctly when hooked up to the 200mv and 1v calibrators. I also have the trace moving on the x and y axis. Anyone have any more ideas as nothing looked amiss inside, no wires hanging, burnt resistors etc. I also checked the voltages, aside from the -1820, and they were all good except for the +12, which I adjusted and have it right where it should be.

author: papo
author_rank: Regular Contributor
timestamp: January 31, 2014, 08:31:41 pm
content: Couple of questions to try to narrow it down:When you have it in single-channel operation, do you see two dots or one, or none at all?I guess this does not work with either of the channels, right?Do you get any change if you manipulate the timebase?My guess is that there is something wrong with the "horizontal switching" block in figure 6-1 of the manual that was posted before. It can't be the horizontal amp, otherwise you would not see the two dots in xy-mode. And it's unlikely that it is the sweep generator since these are separate for each channel and having both of them break is just unlikely.This stuff is shown in schematic 10. I would first stab around in the dark and verify that both sawtooth sweep signals are there before and after the buffer-amplifier (Q1001 and Q1002). Then I'd check Q1003 and Q1004. This circuitry is described starting from page 87. Particularly check figure 6-7 to get an impression. If nothing appears to be wrong there, continue forward.I know this is not the best advice and the components likely have different designators in your scope. Also I'd have to reconsider if you don't see the two dots.HTH, regardsMatt

author: 1jonnyz
author_rank: Contributor
timestamp: January 31, 2014, 08:44:15 pm
content: I get nothing at all on channel 1 or 2, and 1 dot with x/y until I hook up the probe to calibrate then I get the 2 dots which does measure the voltage correctly. Switching the timebase around does nothing, whether on channel 1, 2, or x/y. I can check for the sawtooth signal with another scope?

author: Joule Thief
author_rank: Regular Contributor
timestamp: January 31, 2014, 09:04:59 pm
content: Quote from: 1jonnyz on January 31, 2014, 08:44:15 pmCorrect, scopes are the best tool to fix other scopes.Don't underestimate the value of exercising all the pushbuttons and controls associated with the horizontal section. My beam finder would not function at all until I "bottomed out" the switch a few times.

author: Andy Watson
author_rank: Super Contributor
timestamp: January 31, 2014, 09:33:28 pm
content: An observation: The first two photos show the scope in what looks like a shadow (although it could be a camera trick), given the relative darkness and the fact that cameras usually exaggerate any source of light (e.g. the power LED) - those traces look very dim - especially for stationary spots. I would guess there is something wrong with the brightness or Z-drive.

author: 1jonnyz
author_rank: Contributor
timestamp: January 31, 2014, 10:03:20 pm
content: The beam finder works, but only on x/y mode. I did get a sawtooth on the collector and emitter of Q1104, none on the other 3 though. I also noticed that one side of R1121 is -1000V and the other side is 0V??

author: iDevice
author_rank: Regular Contributor
timestamp: January 31, 2014, 10:04:38 pm
content: Quote from: Andy Watson on January 31, 2014, 09:33:28 pmIt's a good remark, but even if there is something wrong around the Z input and amp or CRT voltages for that matter, because you can see the two dots in xy mode, you should see a moving spot as well in very slow sweep modes.Unless it's the fly-back cancellation circuit of the sweep generator itself that's failing.

author: iDevice
author_rank: Regular Contributor
timestamp: January 31, 2014, 10:18:50 pm
content: Quote from: 1jonnyz on January 31, 2014, 10:03:20 pmInteresting, going back to Andy's remark, it could be Z circuit related after all, but not the circuit itself but what is fed to it from the sweep generator.Normally, the sweep generator should send a very short pulse to the Z circuit during the "dead" portion when the trace goes back to the left of the screen, which is called "fly-back".But if there is something wrong there, it could actually receive a permanent "cut-off" signal instead of this pulse.If this happens, then obviously you won't get a trace at all, which could explain why you don't even see the two dots stuck in the middle of the screen, or any dot at all for that matter, as soon as you use the Y-T mode.When you go in XY, this erase pulse fed from the sweep generator is probably disengaged completely and that's why it works in this mode.

author: 1jonnyz
author_rank: Contributor
timestamp: January 31, 2014, 10:22:47 pm
content: The trace is very bright, I have it turned down pretty low. I also just checked the schematic and the one side of the resistor is going to ground, which would explain 0 volts, duh:)

author: iDevice
author_rank: Regular Contributor
timestamp: January 31, 2014, 10:50:56 pm
content: I didn't have time to look at the schematics yet, but you should try to cut whatever comes from the sweep generator to the Z circuit.Obviously, the flyback would then be faintly visible, but it should give you the opportunity to see the trace if the rest of the sweep gen is working.I guess the best point to interrupt is where the switching between YT and XY mode occur.the path could either go actually through the front panel switch or, most probably, been switched through a transistor.Another alternative would be that the sweep gen being stopped during XY mode doesn't generate the pulse, so there is no switching needed, there would then be only an adder/mixer fed with all Z modulation sources at the same time one of them being the flyback pulse.It's then where everything is combined that this link has to be cut.

author: 1jonnyz
author_rank: Contributor
timestamp: January 31, 2014, 10:59:51 pm
content: Wow, that sounds rather daunting... I don't know that much about scopes yet:)

author: grumpydoc
author_rank: Super Contributor
timestamp: January 31, 2014, 11:34:12 pm
content: Actually, rather than cutting anything a trick which is possible with some Tek 'scopes might be possible.Round the back there are a couple of useful connectors.First is the Z axis input - this is an intensity input. Normally positive voltage (up to about 3V) reduces the intensity of the trace but if you feed a negative voltage in you might be able to overcome the internal Z drive - possibly up to about -25V will do the trick (shouldn't damage the 'scope as the Z input allowable input voltage is 50Vp-p AC).Second is the A gate output - this is the sweep output and should tell you whether a sweep is (trying) to happen, if you can hook a 'scope up to it.The manual I posted a link to has a fault finding flow chart. I would start by following it - basically for the "beam find doesn't work" case it suggests removing, in turn, the vertical, then horizontal deflection leads from the CRT to isolate the problem to the Y amp, Z amp or sweep gen.It (as does the COS6100 manual identified by sync) also has extensive notes on how everything works so it is probably worth sitting down and reading through it which will increase your understanding of how everything hangs together.

author: 1jonnyz
author_rank: Contributor
timestamp: February 01, 2014, 12:04:05 am
content: "The manual I posted a link to has a fault finding flow chart. I would start by following it - basically for the "beam find doesn't work" case it suggests removing, in turn, the vertical, then horizontal deflection leads from the CRT to isolate the problem to the Y amp, Z amp or sweep gen."I did this today Grumpy and I still had no trace, so I assume tomorrow I need to check the Z-Axis amp and the high voltage. I did check all of the voltages today and they were good.

author: jancumps
author_rank: Unknown
timestamp: February 01, 2014, 08:24:15 am
content: iDevice, the two things we have in common is that our scope was defect and that we're from BelgiumI have solved the problem that you need a second scope to measure the sweep generator of a scope, by asking a fellow EEVBlogger from my neighbourhood to come over with his oscilloscope. Two brains work better than one.Mine got fixed.

author: iDevice
author_rank: Regular Contributor
timestamp: February 01, 2014, 10:47:26 am
content: Quote from: jancumps on February 01, 2014, 08:24:15 amHi neighbor !You may be thinking of someone else, as I don't recall having said that I had a broken scope lately.I did buy a vintage scope in the past that I enjoyed fixing, a very cute US navy one I do remember having written about somewhere, maybe that's what you are referring to.And as for fixing a scope with another scope, well... let's say that since I started with electronics as a teenager 40 years ago and being an EE since, I accumulated 6 scopes of different kind and quality in my home lab, so I guess it's easier.

author: jancumps
author_rank: Unknown
timestamp: February 01, 2014, 10:50:04 am
content: I was probably not thinking whily posting

author: papo
author_rank: Regular Contributor
timestamp: February 01, 2014, 09:42:32 pm
content: At first I thought there might be something wrong with the sweep gate but I don't see how you would get the sweep signal without that. I would check for the unblank pulse next (R1177), and look what is happening to it.RegardsMatt

author: 1jonnyz
author_rank: Contributor
timestamp: February 02, 2014, 05:08:38 pm
content: I checked 1177 and it measures 100 ohms. I put my other scope on it but I don't really know what I'm looking for? I am not that well versed in electronics yet.

author: papo
author_rank: Regular Contributor
timestamp: February 02, 2014, 06:20:04 pm
content: Quote from: 1jonnyz on February 02, 2014, 05:08:38 pmSorry, my post was probably not very helpful as I did not explain what I think you should be looking for. The CRT inside a scope controls the beam in three different ways that are rather independent from each other. The first one is vertical beam control. This means that the beam can move up and down according to the channel voltage, or the Y-voltage in X-Y-mode.The second one is horizontal beam control. This means that the beam can move left and right. In X-Y-mode, the beam position is determined by the X-voltage. Otherwise, the X-position of the beam is determined by the sweep generator. This is the sawtooth waveform that you were looking at a few days ago. Basically the higher the voltage from the sweep generator, the more the beam is deflected to the right. One reason for the lack of a trace could therefore have been that the sweep generator was malfunctioning. Typically, such a malfunction does not manifest itself in the total lack of a trace but it was a start.The third way is z-axis beam control. This essentially controls the intensity of the beam and whether the beam is on at all. For example when the beam is sweeping across the screen from left to right, at some point it will hit the right edge of the screen. The beam then has to move to the left hand of the screen to start over, but you don't want to see that flyback on the screen. This is why the beam is turned off during the flyback and turned on again afterwards. This is not the case in X-Y-mode because you are not sweeping from left to right. (You can however use the Z-input to vary the intensity of the beam).Now imagine that the blanking/unblanking circuitry was malfunctioning. In X-Y-mode, you might not notice anything, but otherwise the circuitry might blank the trace permanently instead of just the trace flyback period. This is why I'd check the unblanking to rule this out.Referring to the schematic, it looks like the beam blanking is controlled by the UNBLK SIGNAL on one end of R1177. This should be a pulse / square wave. Whether you see that pulse tells you if you have to look for an issue before or after that spot in the circuit. Unfortunately I cannot find the origin of that signal, I'll have to look harder if the pulse is not there to trace back where between the sweep gate and this resistor things might go wrong.Another reason for your problem could be that even though you are in auto mode, the scope is not triggering. You have a green "triggered" LED on the front panel. Is that on or or off? It should be on in auto mode, but go off when you change to normal mode or single mode. Two other things that you can easily check are the A gate output and the A sweep output at the back of the instrument.All suggested measurements are meant to be conducted in sweep mode, not in X-Y-mode.I hope this was more helpful than the previous post.RegardsMatt

author: 1jonnyz
author_rank: Contributor
timestamp: February 02, 2014, 09:51:29 pm
content: I don't know what the heck happened Matt, but for the first time I have a trace in channel 1 and channel 2! I was able to get a good trace, could move it off the screen and beam finder moved it in. I did just shut it down and restarted it and didn't have a trace again, I messed with the AUTO NORM mode switches next to the time division knob and got it back again?? I don't get the trigger light however, the only time it comes on is when the internal trigger on the left side is set to alt and I am in x/y mode. It doesn't matter if the mode is in automatic or single, I still get no trigger light. I can only measure dc voltage, I guess because the sweeps not working? Thanks for your help Matt!!I should add that the trace that I get is just a dot, and when I use the calibrator I do not get a square wave I just get 2 dots that measure the voltage. The uncal light on the time division doesn't work either, I doubt that that's a clue but maybe.

author: papo
author_rank: Regular Contributor
timestamp: February 02, 2014, 11:20:18 pm
content: Quote from: 1jonnyz on February 02, 2014, 09:51:29 pmUhu OK that sounds like progress(?). First of all, on the triggering: If you have the scope in auto mode, you should always see a trace. If you have it in single mode, the scope remains blank until a trigger event happens. You then have to interact with the scope to proceed. The normal mode is the same, but after a trigger event, the scope automatically waits for the next trigger event.A trigger event can be different things, depending on the scope settings. The most basic trigger is when your input voltage rises above some threshold (=trigger level). But you can also trigger on falling edges, on the AC line frequency and have more complex triggers.Beginners often get confused because they have their scope in normal mode and have their trigger not properly set up. Then the scope never triggers and you literally end up with a completely blank screen without traces. The "ready"-LED should be on, though.Maybe in your case there's something wrong with the switch and you were in normal mode all the time?Quote from: 1jonnyz on February 02, 2014, 09:51:29 pmHm yeah we could dig further into the trigger LED thing. It's also possible that I'm wrong on this one, though. It's been a while since I dealt with an analog scope unfortunately. I'm sure somebody in this thread can tell us the LED state.Quote from: 1jonnyz on February 02, 2014, 09:51:29 pmSo essentially you have two dots stacked on top of each other, exactly like when you are in X-Y-mode and have the cal input on Y?Just to prevent misunderstandings: The uncal LED turns on when you use the fine-scale adjustment. It does not mean that your scope is generally out of calibration or something like that.It is sort of weird that before, the sweep generator appeared to be working but the unblank pulse presumably was missing, and now you observe the exact opposite. I would triple, check your settings just to be sure. Also in the last picture you posted, I believe you the input on AC coupling. If you want to properly see the square wave, you should go for DC coupling.I still think that it would be a good idea to measure the two outputs I mentioned in my previous post. That would be a nice starting point for further debugging.Regards and good luckMatt

author: papo
author_rank: Regular Contributor
timestamp: February 03, 2014, 03:36:10 am
content: OK just checked. Of course in auto mode the Triggered LED is typically not lit, but the sweep is kicked off anyways. So that appears to be fine. I got confused because one of my scopes actually has the Triggered LED on when in auto mode. This is not an analog scope, though.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 03, 2014, 02:43:22 pm
content: If things are mysteriously startng to work might be worth a squirt of switch cleaner into all the push switches and operate them a few dozen times each. Sometimes that's all that's wrong with older 'scopes which haven't been used for a while.

author: 1jonnyz
author_rank: Contributor
timestamp: February 03, 2014, 07:38:51 pm
content: Quote from: papo on February 02, 2014, 06:20:04 pmI checked for a pulse or square wave and get nothing but voltage. I checked a lot of resistors, ic's, and transistors on that side of the scope and get no wave forms at all, just voltage. I did check my Tek by hooking a signal generator to it and it was displaying wave forms fine, so it's not that.Quote from: papo on February 02, 2014, 06:20:04 pmThe trigger light is only on in x/y mode. I checked both the A sweep and the B sweep outputs on the back via my Tek and get no signs of life there. I also tried the Ch.1 output on the back and it worked fine through my Tek, so I guess that's a good thing! I don't have an A gate output, the only other one is the z axis input.I did find out that the only way I can get a trace when I fire this thing up is to first hit the single button, underneath of the auto, normal mode array, and then hit the auto button. If I start it up with the auto or normal button already pressed in I get no trace, not until I hit the Singl push to reset button.Quote from: grumpydoc on February 03, 2014, 02:43:22 pmI did deoxit the switches I could get to, I will have to try harder to get to the pushbutton switches!

author: papo
author_rank: Regular Contributor
timestamp: February 03, 2014, 10:16:49 pm
content: Quote from: 1jonnyz on February 03, 2014, 07:38:51 pmYes I was wrong on the trigger light. Did you also check for A sweep after the start-with-single-then-hit-auto trick to display the trace? And the other day you managed to display the sweep sawtooth, right? Getting the sweep inside the scope, but not at the output narrows it down a little bit. In some cases, I would expect to have the internal sweep, but not the external one, though.Quote from: 1jonnyz on February 03, 2014, 07:38:51 pmBut when you do this, do you get two dots or a "real" trace? Maybe it's two independent problems: The blank screen thing sounds like the scope is stuck in normal or single mode when starting up. Apart from mechanical button-weirdness, this could be attributed to a broken flip flip used to track the state, or something surrounding those flip-flops. You could use the following approach to test that hypothesis: Instead of using the internal trigger, set the trigger to "LINE". This will trigger off the AC line, at 50 Hz or whatever your mains frequency is. If the screen really is blank because it's waiting for a trigger, that should sort it. Then you should also have the sweep waveform at the A sweep output.The "dots-instead-of-trace" problem could be a separate one. We know that you are getting at least an internal sweep signal. We also know that your scope is capable of deflecting the beam to the left and right, otherwise you would not be able to get two horizontal dots in X-Y-mode. So something in between must be broken.Quote from: 1jonnyz on February 03, 2014, 07:38:51 pmIf the blank screen can be attributed to the auto trigger not kicking in, we'll have to investigate these push-buttons and the state machine related to them.RegardsMatt

author: 1jonnyz
author_rank: Contributor
timestamp: February 04, 2014, 02:34:41 am
content: Quote from: papo on February 03, 2014, 10:16:49 pmI did check for A sweep after restarting and nothing Matt. I made a mistake the other day as far as the sawtooth goes. I found out today that I can't go through my isolation transformer, it's an old RCA and I have to use a 3 prong to 2 prong adapter and it was giving me felonious readings, so no I didn't have a sawtooth. I rechecked Q1001 thru Q1004 and all I get are voltage readings on my Tek, it doesn't matter where I probe I get no sine waves, sawtooth, nothing.Quote from: papo on February 03, 2014, 10:16:49 pmI just get one dot. I set the trigger to A and still got nothing out of the A gate output in the back.

author: papo
author_rank: Regular Contributor
timestamp: February 04, 2014, 10:36:09 pm
content: Quote from: 1jonnyz on February 04, 2014, 02:34:41 amOK no problem, so no sweep then.Quote from: 1jonnyz on February 04, 2014, 02:34:41 amIt's a bit weird that you don't have the A sweep output, page 31 of the manual shows several connectors on the back and both are there. But since this is not exactly the same scope, maybe that is one of the differences.Anyway, which switch is it that you set to A? Because there is two controls. One is INT TRIG which you can set to CH1, CH2, CH3 or ALT. This is only active if the trigger source control is set to INT. It's not active if it is set to LINE. How exactly do you set the trigger to A? (I don't see any lever position saying A).Also the one dot that you get. Is that with the probe hooked into the calibration output or not? Make sure to set your input coupling to DC anyways, but that shouldn't affect this too much.Do you have IRC or something? It's probably a bit easier if we have a faster turn-around than one message per day to track this down.RegardsMatt

author: 1jonnyz
author_rank: Contributor
timestamp: February 04, 2014, 11:47:53 pm
content: It's a bit weird that you don't have the A sweep output, page 31 of the manual shows several connectors on the back and both are there. But since this is not exactly the same scope, maybe that is one of the differences.The 6100M only has A gate ouput, but no A sweep output.Quote from: papo on February 04, 2014, 10:36:09 pm

author: papo
author_rank: Regular Contributor
timestamp: February 05, 2014, 12:00:37 am
content: HelloQuote from: 1jonnyz on February 04, 2014, 11:47:53 pmAh right, OK.Quote from: 1jonnyz on February 04, 2014, 11:47:53 pmOK but wait... are yousureyou are not in X-Y-mode, either accidentally or due do some weird quirk of the scope? My understanding was that X-Y-mode works. If that's the case, you are most likely ending up in X-Y-mode and the blank screen is still the main problem... right?Quote from: 1jonnyz on February 04, 2014, 11:47:53 pmOK I'm suggesting to stick to the board as somebody might have something to add to what we are doing, or might benefit from it. But if people complain I'll happily move to PM.RegardsMatt

author: 1jonnyz
author_rank: Contributor
timestamp: February 05, 2014, 12:50:48 am
content: Quote from: papo on February 05, 2014, 12:00:37 amNope, not in x/y mode. x/y was the only time I could get a trace (dot), then I discovered I needed to hit the single/reset button then auto to get a trace (dot). I can turn the scope on while the mode is set to channel 1 or 2 and there is no trace, even with the auto button (next to the time/dive knob) pushed in. The only way I can get the trace is to first hit the single/reset button and then auto or normal mode button.BTW, i built an octopus curve tracer last year and hooked it up to ch1 and ch2 and put it in x/y and was able to get lissajous patterns... capacitors were ellipses etc. Don't know if that helps but figured I'd let you know!

author: papo
author_rank: Regular Contributor
timestamp: February 05, 2014, 02:29:30 am
content: Quote from: 1jonnyz on February 05, 2014, 12:50:48 amI see. So if you set up the scope for X-Y-mode (I understand this is not what you just described), then you see one dot if nothing is connected, two horizontal dots if you connect the cal to the X-input (channel 1) and two vertical dots if you connect the cal to the Y-input (channel 2). I hope I didn't get this wrong. I think that what you observe in X-Y-mode is exactly what you should see, hence so far everything is fine.The really strange part is when you do the single/reset/auto sequence when DISPLAY is set to A and MODE is set to CH1. There is several things that should not be the way you describe it: First, you should never get two horizontal dots in this mode. So my first thought was that for some weird reason, you end up in X-Y-mode if you do this even though the X-Y-button is not active. But then I re-read what you wrote and you see two vertical dots when the cal is connected to CH1 and two horizontal dots when it is connected to CH2, so that's exactly the opposite of what X-Y-mode should give. Right now, I'm not sure how to interpret that.If DISPLAY is A and MODE is CH1 and you don't do the single/reset/auto sequence, you get a blank screen even if trigger MODE is set to AUTO. That's also not exactly what you should get. As far as I can see, possible explanations are:The auto trigger generator is broken.The scope does not realize it is in auto mode and waits for a trigger.The scope thinks it is in single mode and either waits for a trigger or does nothing.The scope constantly blanks the beam.Could you check the following, with the settings as described above and the trigger source lever in the LINE position?Pin 4 of U1002. This should give you a voltage and tells whether the scope recognizes that the A button is pressed.Pin 1 of U306. Same, for CH1 button.Pin 5 of U303. Same, for X-Y button.Is the READY LED on?Do you read a voltage on the anode of CR722?Pin 3 of U505. This might be a square wave.The ready LED and the diode tells about the state of the Auto/Normal/Reset buttons. The last test checks whether the auto trigger generator is broken. Please make sure these are all done under the conditions Auto mode, Ch1, display A and trigger LINE.Quote from: 1jonnyz on February 05, 2014, 12:50:48 amThat's cool. If you want further clarification whether X-Y-mode really works, I think you could try to replicate that with this scope, or hook up a function generator or something. The issue is that you are feeding it a square wave from the cal output, which has many values at 0 V and many values at 1 V but hardly anything in between since the edges are quite fast. Hence, the line between the two dots that one might expect may not be visible. You get the same effect if you look at a square wave in sweep mode with an analog scope: You can see the high and low levels but you don't see the edge because it's so fast. (Of couse this depends also on the time base and the beam intensity).HTH, regardsMatt

author: iDevice
author_rank: Regular Contributor
timestamp: February 05, 2014, 09:27:53 pm
content: Quote from: 1jonnyz on February 05, 2014, 12:50:48 amCould you clarify something here.You write that in this case you get a trace, but you also write (dot).A trace being the opposite of a dot (a trace would be straight horizontal line if there is no vertical signal), can you elaborate on what you really see.Could you also tell us if it's only during one very brief moment, or does the trace or dot stays on until you try something else.If it actually is like I think it is, you get a dot in the middle of the screen for a fraction of a second ?Then that would mean, the sweep generator is broken, or at least there is no sawtooth fed to the horizontal amplifier.The fact that that dot appears would be only due to to the blanking signal (flyback cancelation) being reset for a brief moment when you make this sync mode selection.And it would make sense all along.On most TB designs, the beam is blanked by default when the TB mode is engaged (non XY mode) and it is only when a sweep is actually triggered that a signal goes to the Z channel to turn the beam on.So if there is no sweep generated either because the sweep generator is broken or the sync circuit does not triggers it, there won't be any beam visible, ever.Now, we have to determine if the failure is in the trigger circuit or the sweep gen itself.

author: papo
author_rank: Regular Contributor
timestamp: February 05, 2014, 09:57:00 pm
content: Quote from: iDevice on February 05, 2014, 09:27:53 pmI interpreted "I get a trace" as "the beam is not blanked (or out of screen)" but I was wondering about the same.Quote from: iDevice on February 05, 2014, 09:27:53 pmAnd that "ever" refers to TB mode only. I think that the dots are all related to X-Y-mode. If you think about it, OP can generate horizontal dots in "TB" mode using the quirky sequence of buttons, but other than that the screen is blank always. This sort of indicates that this is not really TB mode after all, but I'm baffled by this. It doesn't really fit into the whole trigger/sweep issue idea that we're discussing.Save from this quirk, never is there anything on the screen in TB mode. That's why I also think that this is either a triggering issue or a sweep gate/generator issue, tending towards the former because if the sweep generator is broken, there still should be a sweep gate pulse IMO, as this pulse kicks off the sweep generator. This pulse is generated by the second half of U704. This might be an interesting point to start off, checking whether the issue has to be sought before or after U704.I'm really eager to know about the measurements about the autotrigger measurements and the LINE trigger test, as these might shed some more lights into this.RegardsMatt

author: 1jonnyz
author_rank: Contributor
timestamp: February 06, 2014, 07:00:37 pm
content: Quote from: papo on February 05, 2014, 02:29:30 amThat is correct Matt.Quote from: papo on February 05, 2014, 02:29:30 amI get no voltage at Pin 4 of U1002. I don't get any voltage whether I am in Auto, Normal, or Single. I do get voltage if I change Display to Alt or B Delayed.Pin 1 of U306 shows no voltage with channel 1 pushed in.Pin 5 of U 303 shows no voltage whith x/y pushed in.Ready light is NOT on.No voltage at the anode of CR722 with Auto in. I do get voltage with either of the other 2 buttons in.I apologize for not being on here in awhile but we had a major ice storm here and had no electric and internet for almost 2 days!!

author: 1jonnyz
author_rank: Contributor
timestamp: February 06, 2014, 07:04:06 pm
content: Quote from: iDevice on February 05, 2014, 09:27:53 pmI get a dot and that's it. The dot stays on the whole time. When I use the calibrator I get 2 dots as I posted previously. The 2 dots will measure voltage correctly also.

author: papo
author_rank: Regular Contributor
timestamp: February 06, 2014, 07:48:03 pm
content: Quote from: 1jonnyz on February 06, 2014, 07:00:37 pmThis is correct. Pin 4 is generally pulled up by R1040 but can be grounded by A or A INT.Quote from: 1jonnyz on February 06, 2014, 07:00:37 pmThis is also correct. The pin is pulled up by R1340 and grounded through the CH1 switch.Quote from: 1jonnyz on February 06, 2014, 07:00:37 pmOK, that's correct also. The voltage should change however when you are not in X-Y-mode.Quote from: 1jonnyz on February 06, 2014, 07:00:37 pmI think the only way for the ready light to be potentially on is when you are in single shot, waiting for a trigger. So that looks OK, too.Quote from: 1jonnyz on February 06, 2014, 07:00:37 pmThis looks OK as well. So far everything seems to be correct, hence I think we should proceed with the trigger stuff. Pin 3 of U505 is a good starting point IMO. Also Pin 11 of U704 could be interesting, as this is the input to the sweep gate generator. Do both measurements under the following conditions: DISPLAY A, MODE is CH1, Trigger mode AUTO, Trigger source LINE. If you don't get pulses there, the problem is before this point. If you have pulses, it is after this point.Quote from: 1jonnyz on February 06, 2014, 07:00:37 pmDon't worry dude, it's not like there is a deadline for this or anything. I hope the weather is getting back to normal soon.RegardsMatt

author: iDevice
author_rank: Regular Contributor
timestamp: February 06, 2014, 08:43:16 pm
content: Quote from: 1jonnyz on February 06, 2014, 07:04:06 pmWow, but this is very important information !It means you are actually staying in XY mode when this occurs instead of the YT mode.So if I understand correctly, you select a timebase mode (single, if I remember, and pushing reset ?) but you still can see the two horizontal dots when you input the calibrator signal on ch1 ?That would mean that although the scope should be in YT, it actually remains (at least partially) in XY mode.I say partially because, the blanking becomes enabled but the TB is still disabled and Y channel 1 is still routed to the X channel instead of the output of the sweep gen.And by some manipulation you get into a twilight mode where the blanking get disabled.But like Matt said, I'm also baffled by the fact you say you see the 2 horizontal dots when calibrator applied to ch2 as this doesn't make sense then.Anyway, this could be just a mode selection malfunction in the front panel logic or elsewhere on the way.

author: 1jonnyz
author_rank: Contributor
timestamp: February 06, 2014, 09:06:17 pm
content: Quote from: papo on February 06, 2014, 07:48:03 pmI get voltage at pin 3 of U505 and I also get voltage at pin 11 of U704, I don't get pulses though.

author: 1jonnyz
author_rank: Contributor
timestamp: February 06, 2014, 09:17:46 pm
content: Quote from: iDevice on February 06, 2014, 08:43:16 pmThis is what I see when I am looking at the 1 volt calibrator hooked to channel 1. The only way I can get the dot to show up when I start the scope is to first hit the single/reset button and then auto. If it is set to AUTO when I start the scope it will show nothing, same with NORM, it is not until I hit the reset then auto before I see the dot.

author: papo
author_rank: Regular Contributor
timestamp: February 06, 2014, 09:23:49 pm
content: Quote from: 1jonnyz on February 06, 2014, 09:17:46 pmI'm sorry to re-iterate over this, but if you have the scope set up exactly like you showed in the picture and then change the BNC connector from CH1 to CH2, do the points become horizontally aligned? Because I think this is what we understood and we both are very confused by this.RegardsMatt

author: 1jonnyz
author_rank: Contributor
timestamp: February 06, 2014, 09:30:48 pm
content: Quote from: papo on February 06, 2014, 09:23:49 pmNo they are still vertical Matt, only when in x/y mode do they change their axis when going from channel 1 to channel 2. Did I say at some point earlier that it changes axis when not in x/y mode? I apologize if I did!

author: iDevice
author_rank: Regular Contributor
timestamp: February 06, 2014, 09:41:35 pm
content: Quote from: 1jonnyz on February 06, 2014, 09:30:48 pmUh, confused again... If you go to XY mode when you are in this situation, the dots should go horizontalwithoutchanging input channel...When in normal YT mode, Ch1 is a vertical channel.And on most scopes, in XY mode, ch1 becomes the x channel, it may be strange but it is the convention.Edit:BTW, your Time selection knob seems to be missing a piece, are you sure the whole thing still exists behind it ?

author: 1jonnyz
author_rank: Contributor
timestamp: February 06, 2014, 09:51:02 pm
content: Quote from: iDevice on February 06, 2014, 09:41:35 pmYou are right, when I stay connected to channel 1 and then change to xy the axis does change to horizontal.Also, I had to remove the time division assembly to get to the one diode to test it.

author: 1jonnyz
author_rank: Contributor
timestamp: February 10, 2014, 01:14:34 pm
content: I was messing with this yesterday and testing some capacitors and found C901, a big plastic film 1uF 200V, on the B Sweep board that is shorted. I also found some 10uF electrolytics that are reading way high, about 30uF. I am wondering if these could be what is causing my problem? I have some new ones ordered.

author: papo
author_rank: Regular Contributor
timestamp: February 19, 2014, 12:18:03 am
content: HelloFirst of all, sorry for being away for a couple of days. I got massively overloaded with work-related stuff.Quote from: 1jonnyz on February 10, 2014, 01:14:34 pmThis is very, very interesting. I have to re-check the schematics thoroughly, but if I am not mistaken, C901 is one of the timing caps of the integrator for the sweep integrator. Having that guy shorted would explain the lack of a sweep signal. I'm not sure whether this is already obvious from physically looking at the boards, but C811 is the equivalent for the A sweep generator. You could compare your measurement to that one, although from a quick glance at the schematic, I don't see how either of the two can be shorted in-circuit. (Sometimes, components appear to be shorted because of other components even though they are fine but that does not seem to be the case here.) So you might be onto something and should really investigate C901 (and C811) further. For example, if you unsolder the cap, is it still shorted? If so, I'm quite confident that you found one of the problems. If it's not shorted, but you can measure a short "across" the (missing) cap on the board, I have to re-check the schematic.As for the other caps, that's really tricky to say. Standard electrolytics have quite a high tolerance, but the typical failure mode is that their capacitance drops. So if I had to guess, I'd say that's it's less likely a real problem than not, but you never know. Also, I guess you made these measurements in circuit, so there's also the chance that some other capacitor is in parallel with the one you measured, which would also explain the high measurement.RegardsMatt