Author Topic: 11301 - basic analog scope troubleshooting help needed  (Read 4690 times)

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Offline cncjerry

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11301 - basic analog scope troubleshooting help needed
« on: July 27, 2017, 08:52:18 pm »
I have the power supply out so I can't post a picture but the issue is easy to visualize.  If you have a square wave displayed and the vertical edge is aligned on the grid (anywhere) the top and bottom horizontal sections of the square wave overlap.  Looking at the signal, you can see excessive jitter in the horizontal (X) axis.  At first I thought it was related to focus but changed my mind. 

I've looked at as many Power supply voltages (+/-5; +/- 15; +50) as I can and don't see anything in terms of ripple that is excessive.  On all the voltages there is a very slight noise ramp up that seems to reset every two seconds.  The noise ramp up is in the low millivolts and maybe hits 10mv on +5 when it seems to reset.  All the caps look good and I plan to check the ESR while I have the supply out.

So basically I think there is a horizontal time base problem or it could be in the trigger. I would think that if it was the trigger that changing the trigger level and/or type would have some impact on the signal trace but it doesn't.  This unit has option 1T which adds a DOCXO and disconnecting it has no impact on the horizontal signal.  Without the schematics I think the DOCXO is used for the integrated counter.

As I mentioned in the earlier thread, the text is all pretty crisp and easily aligned so the basic scope display through the vertical and horizontal amps are probably ok.

The big issue with repairing this scope is that the schematics aren't available.  It's a board swap for FRUs.  I have the service manual as well as the calibration software running.  I've tried some of the automatic calibration options in the software without luck.  I've tried various vertical amps and they all check out OK in this unit as well as my DSA602.  I would really like to get this beast running to have a 400Mhz analog scope but so far, no luck.  The signal is visible and I can use if for some work, but with the trace being so wide, about .1 divisions, it is not very practical.

I've looked at some of the sync and other signals that are brought out the back and don't see much jitter in them, if any.  Other than the slight noise pulse across all voltages everything looks clean.
« Last Edit: July 27, 2017, 09:51:18 pm by cncjerry »
 

Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #1 on: July 27, 2017, 10:44:13 pm »
I checked the power supply to the extent possible and it all seems fine. 

You can see in the attached picture how the flat top of the square wave extends past the 4th graticule square and the bottom flat starts near the same graticule.

Hopeless without a schematic and a ton of specialized alignment gear?

I was able to scavenge the three vertical amps plus I can pull the Isotemp 10Mhz oscillator so this is some gain from a freebie.

I would like to see it work though.

thanks for looking.

Jerry

 

Online TerraHertz

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #2 on: July 28, 2017, 12:50:01 am »
What is the source of the displayed square wave?

Can you adjust the Horizontal Position knob, so the trigger point at the left is displayed on screen, turn the timebase to the next slower sweep speed, and take another picture please?

The trace you've posted, looks to me like the scope may be OK, and the source square wave has varying frequency or mark-space ratio. You are seeing the phosphor averaging of a lot of falling edges with slightly different timing. Can't see the actual vertical edges because they are fast, and the scope has decent bandwidth. This is quite unlike what you'll see with a digital scope display, which in line-draw mode will show the edges.
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #3 on: July 28, 2017, 12:57:00 am »
The source is the calibrator which looks fine on my other scopes (I have about 10 or so).  I put many other known signals into the scope with the same result.  A sine wave looks like it was drawn with a .1 division marker held horizontally as it traces the wave.  The jitter is all in the horizontal direction.

One interesting point is that if I zoom in on the signal so I have one very light trace at the trigger point, the trace doesn't look that bad for some reason.  I think it is because the lighter traces are washed out. 

I'll post others shortly.

 

Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #4 on: July 28, 2017, 02:05:53 am »
Here's two more shots.  On the first I was trying to show the left edge where it triggers but it is tough to see as there is so much horizontal jitter there isn't enough trace to display an edge.  The second is just more of the same square wave showing more overlap.

There could still be a power problem I can't find but I've been all over the rails looking for ripple.  Other than that noise pulse I mention which could be related to something like the counter gating (i've turned it off without any luck) I think the power is fine.

 

Offline tautech

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #5 on: July 28, 2017, 02:16:09 am »
Nah, it's not right and could need just a case of the good ol' follow the signal path detective work until you find where it all goes bad.
Is it full of unobtainium IC's ?  :scared:
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Offline tautech

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #6 on: July 28, 2017, 03:15:45 am »
Further thoughts.......
I've seen some funny stuff on displays when the sweep ramp sawtooth waveform is not nicely linear ..........reasonably easy to check with another scope.
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #7 on: July 28, 2017, 03:30:47 am »
the sweep ramp output which is exposed on a BNC looks fine, no jitter.

This scope is huge if you haven't seen one.  It is the size of a full-sized microwave, crammed with unobtainium custom ICs, discrete logic chips and no schematics.
 

Offline WastelandTek

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #8 on: July 28, 2017, 03:53:45 am »
dude...you have invented time travel



ok, to be more helpful, is it some kind of severe geometry error, like an hourglass?  If you vert position it up and down does it change?
« Last Edit: July 28, 2017, 03:57:00 am by WastelandTek »
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #9 on: July 28, 2017, 04:42:54 am »
no, imagine the vertical sections of the square wave being spread over about .5 grat divisions and washed out because they aren't overlapping on the phosphor to create a solid vertical line.  The horizontal sections overlap and that is why they are bright.  Remember on an analog scope the phosphor retains the persistence so unless the phosphor is hit continuously it goes dim and you don't see a vertical line.  If there was a jitter problem in the vertical amplifier, the vertical lines would be bright and the horizontal lines would be so dim as to not be there.

So this is a timebase issue, I assume, or some kind of triggering problem.   When I can zoom in on the trigger point I can see a very dim line so if it was a trigger issue you would think I would see multiple line sections. I am going to try to eliminate the trigger as an issue by trying external triggering with a T connector on the same signal.
 

Online TerraHertz

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #10 on: July 28, 2017, 07:02:14 am »
http://w140.com/tekwiki/wiki/11301   for those wondering what it looks like. Sadly, no manuals there.

OK, that's interesting. Having a pretty clean vertical edge at the trigger point, offset 25% from the screen edge, suggests it can't be noise in the horizontal amplifiers or manual offset signal. I wonder if the clean sweep ramp you can see on the output connector, is the same as the one used to drive the H-amps? Or is there another amplifier stage in between?

Hmm... If you used another scope to look at the signal on the CRT H deflection plates, surely that amount of rate jitter should be visible. Follow it back from there?

The tek-wiki article says the scope is programmable. I wonder if that means the H-offset is programmable too? If so, is that summed together with the manual offset? Or what? And how does the sweep rate programability work?

Btw, are there on-screen readouts available? And are they stable when visible? Does enabling them make any difference to the signal display problem?
« Last Edit: July 28, 2017, 07:06:52 am by TerraHertz »
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #11 on: July 28, 2017, 04:29:54 pm »
the text is pretty good with all the covers on but I get some wavy lines depending on how much is on the screen, brightness, etc and the covers are off.  The text adjustments have no impact on the trace but there seems to be a difference in vertical focus between the characters and trace which can be evened up with all the pots.  I mentioned in an earlier post that there are over 10 pots that effect the character display like the corners, horizontal and vertical centering, etc.

One thing I noticed last night was a signal where I check the voltage ripple that is clearly jumping arounds.  I don't know what the signal is though,

As far as looking at the deflection plates, I have a feeling this is a dual beam scope of some type because the trace seems so independent of the text display.  Or the scope is treating the horizontal as if it was a jittery signal so tracing back from there wouldn't buy me anything, not that it isn't a bad suggestion.  I'll post some pictures of the boards, these are a work of art.

I have a feeling there is something wrong in the timebase for the sweep.  The A14 board is listed as the timebase board and I was going to go poking around there today.

One other piece of info in this mystery is that the higher frequency signals have less jitter.   You would think a timebase problem to impact higher frequencies more, no? 
 

Offline WastelandTek

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #12 on: July 28, 2017, 04:52:17 pm »
...with all the covers on but ...

man Jerry, just like my comment in the other thread, when I had behaviors like this it ended up being RF in the shack, what are you using for lights in there?
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #13 on: July 28, 2017, 06:20:15 pm »
Waste.  I can see some ripple from the lights with the covers off in the text but not in the trace.  I don't have any strong RF around it and had the same results in my garage as in the workshop.

Here's what I'm dealing with and no schematics.  The upper left set of pots help with the character focus.  The upper right side is the timebase area, mostly for horizontal.  I can shift the overall display left and right and tune it with the pots in that section but no specific impact on the trace.  The lower right of the board is the reference generator and counter logic.  The lower left is the DAC which sets all the voltages under program control.  This could be the issue as well - bad cal data but I can't find a specific test or adjustment in the calibration software that impacts the horizontal jitter.

I am also reposting a picture of a sine wave I took prior to understanding the trace width being a problem.

I've been probing in the upper right this morning trying to find some jitter but I see nothing specific.  I was going to hang two scope probes on the pins that are on the two white wires in the upper center of the board above the two wide connectors.  I should be able to get an XY on my other scope as those are going to the horizontal deflection amp (I assume as they are only around +40v).  the pot to the right of those wires sets the ripple for the text but not for the trace.

As I mentioned previously, I scavenged three vertical amps and get pull the DOCXO (don't need it because I have a GPSDO system).  The amps I used in my DSA603 (cool device as well).  But as I stated a few times, I would love to see this tuned up as I like having an analog scope around.  I have two 7603s but they are limited to 100Mhz.

thanks for all the input, keep the ideas coming.

Jerry



 

Offline StillTrying

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #14 on: July 28, 2017, 07:12:38 pm »
From the underexposed first half-peak of the sine it looks like it might be astigmatism.
Does the tube look like it has 2 beams.
Is it possible to turn the brightness well down and look at the shape of the dot, maybe in XY mode.
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #15 on: July 28, 2017, 07:19:04 pm »
yes, it does look like astig but only on the trace, not the characters.

There is a focus and astig adjustment on the Display menu but it only adjusts the vertical component of astigmatism, not the horizontal.  I looked around in the calibration software and can't find a function to adjust it either.  Note in the sine wave trace that the characters aren't bad, just the trace.

You can't see it in the pictures but you can barely see the vertical lines tracing within a space of about .1 or so graticules. On some settings, some of the verticals you can see are slightly brighter than others meaning that the distribution of the vertical traces (that are out of alignment) is not equal.  So something is jumping all over the place.

I am going to try and XY trace to see what it looks like.

 
 

Offline StillTrying

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #16 on: July 28, 2017, 07:37:00 pm »
CML+  That took much longer than I thought it would.
 

Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #17 on: July 28, 2017, 08:16:38 pm »
wrt: two beams, it's just sort of weird how the roughly 15 variable resistors, caps, etc impact only the text and not the trace with the exception of overall centering.

Playing around with the triggering, it looks like it is stable on the trigger edge and overlaps as the trace runs out.  I scoped the sweep output and it looks stable.  I am attaching a picture of the left edge when set to a negative slope.  You can see it looks better than the following edges.

I wonder if calling Tektronix would free up a set of schematics...

Thanks for the pointers again.

 

Offline tautech

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #18 on: July 28, 2017, 08:30:17 pm »
I am attaching a picture of the left edge when set to a negative slope.  You can see it looks better than the following edges.
The little steps in that falling edge don't look right to me..............  :-//
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #19 on: July 28, 2017, 10:41:24 pm »
I've seen those steps on the calibrators on both my 11301 and DSA602.  I think they use a DAC to generate the signal.  There are several frequency options and on the DSA a DC option for the calibrator output.  I checked the output with my TDS3054b and it is the same.

I really like this scope.  It has a lot of features for an analog beast, windows, multiple delays, lots of measurements, integrated 750Mhz counter (with and DOCXO).  I've been looking for another one actually if I can't get this one running, maybe I can find a 11302a for cheap.
 

Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #20 on: July 28, 2017, 10:58:49 pm »
Let's go back to the timebase for the horizontal sweep.  The sweep ramp looks ok with no detectable jitter.  Shouldn't I be able to find a crystal someplace that is divided down to the horizontal timebase?  I found one where the DOCXO feeds into the counter but this doesn't seem to impact the sweep as I can connect/disconnect it and the only error I see is from the counter where it says the counter PLL isn't locked.  I've located the timebase board and can find anything that looks like a clock or timing generator.  Ideas?

 

Offline StillTrying

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #21 on: July 28, 2017, 11:10:26 pm »
I can't think of anything that explains all of what you see on the traces.
If you do try to get some 0s and 8s displayed in XY mode, it might help to eliminate some things such as the X ramp and triggering.

http://69.16.194.131/prod/MTAyMTg0MjE0/Tektronix-11301A-Digital-Oscilloscope-CRT-154088300-eBay
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Offline tautech

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #22 on: July 28, 2017, 11:55:41 pm »
Let's go back to the timebase for the horizontal sweep.  The sweep ramp looks ok with no detectable jitter.  Shouldn't I be able to find a crystal someplace that is divided down to the horizontal timebase? 
Normally they are just an assortment of RC combinations but how they're generated in this Tek I'm not sure.
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #23 on: July 29, 2017, 05:42:11 pm »
So it looks like a trigger problem which I don't understand.  I played with the various options and after careful tweaking I was able to get it to lock.  The pictures aren't perfect, but they are much, much better than prior traces.  For a few minutes I was thinking it was all operator problems, but I can't change the size of the vertical or horizontal and keep it triggered like this.    But it points me in a new direction at least.  So I am going to go back to the calibration software and explore the various trigger calibration options.

 

Online TerraHertz

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #24 on: July 30, 2017, 12:14:02 am »
Dammit, yesterday morning I wrote up a medium-long reply, then hitting Post got that blasted Gateway Error. Post gone, can't recover it. Then went out for a day bushwalk, during which I got a twig whiplash in the eye, so now will be off to the doctor.

Anyway, briefly: Put this scope in XY mode. Take the cal sig out from this scope, feed it to its Y input and a channel input of another analog scope. Trigger that other scope on the signal. Take that scope's sweep output ramp, and put that into this scope's X input.
Result after adjusting XY gains and offsets on this scope - it's acting just like a scope should, but you have eliminated this scope's triggering and timebase from the display process. Also you have a correct waveform displayed on that other scope, to compare against what you see on this one.
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #25 on: July 30, 2017, 01:02:08 am »
Interesting, TerraHertz, it might take me a day or two to set that up as my other analog scopes are 3 floors away, but that is an cool test.

In the pictures above, I had two pretty nicely locked displays that I couldn't repeat without a lot of work. Actually gave up earlier today. So I think it has a nasty triggering problem.  It shouldn't be amplitude as the vertical amps have been tested in my DSA602.  The backplane though could be screwing with the amplitude but it looks OK on the scope.

Thanks for the input.
 

Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #26 on: July 30, 2017, 02:48:44 am »
OK, so how do you figure this one out?  Setting aside some of the autoset calibration issues, I can now reliably trigger a signal and get rid of that jitter.   The main trigger light is on when it is jittery and also on when I tweak it very carefully so I can't figure it out.  The scope has at least 3 levels of trigger sensitivity plus AC, DC, HF reject, LF reject, etc. etc.  It is pretty complete.

The pictures don't do it justice with the blooming,  especially on the 7603 equivalent picture, and I agree it still has a problem but it could be all calibration.   Of all the pictures, the best on-screen display is with the 7603.  It is pretty amazing how good it looks as I used a blue translucent custom fit filter since it came with an RF shield I had to pitch. 

I'm not suggesting it doesn't have a problem, but for what I might use it for in the future twiddling with the trigger is tolerable.

I know I'm not the first person that wanted the schematics for the 11000 series.

btw: This is a calibration signal at 1Mhz listed as 'fast' on the 11301 calibration menu.  The 7603 and 3054 were on a longer cable than the 11301.

« Last Edit: July 30, 2017, 03:08:27 am by cncjerry »
 

Online TerraHertz

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #27 on: July 30, 2017, 11:31:21 am »
By the way, why are those test 'square' waves so terrible? Are you running a source cal output via coax directly to the scope channel input BNC, without a terminating 50ohm pad? Thus getting lots of reflections in the coax. All that ringing can cause triggering instability if you aren't careful with trigger mode and level.

This makes me wonder if maybe some of your test setups before were using cal signal paths with poor shielding/grounding/termination, and the ringing plus some external noise source (RF in the lab?) adding HF noise, caused triggering jitter.

If you are used to using low BW scopes (100MHz) and now trying a 500MHz one, part of the problem may be that you aren't used to the extra weirdness that happens at higher frequencies.

With edges that have a lot of ringing, you should be using HF DC trig mode, ensure the trigger edge is on screen, and trigger at a point on the edge that is reasonably free of timing ambiguity. A nice clean rising/falling part of the edge.
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Offline StillTrying

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #28 on: July 30, 2017, 02:39:49 pm »
I don't think there's enough evidence to say it's a triggering problem, and we won't know until you get some very clean test signals. :)

I'm sure the strange dots on the falling edge in #17 are due to the strange ringing shown in #26.

« Last Edit: July 30, 2017, 03:17:54 pm by StillTrying »
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #29 on: July 30, 2017, 04:12:57 pm »
Most of my equipment goes to 3Ghz+ with my analyzers up to 20Ghz and I've worked with RF for almost 50yrs.  These signals are what I have handy as I moved the scope to a place where I can work on it but I moved most of my test equipment out of my shop.  So I am using the square waves from the calibrator on the 11301 which I think is 450ohms.  The cable going to the 7603 and the 3054 is 75ohms and pretty long, maybe 4 meters, as the 7603 is far away.

This signal is called a fast square wave on the 11301 menu opposed to the other signal on the prior thread.  I have a feeling though no proof that the other signals are DAC generated consequently you can see the steps.  I am pretty sure it is the same on m DSA602 where you can see the steps as well.  Some of my Tek scopes can't drive a 50ohm load from the calibrator so I've been keeping the scopes in 1Meg or higher impedance, just using cables.    But I've tried looking at signals with proper probes and connectors with the same results.  I have an issue with strong FM signals that always show up around 100.3Mhz but the jitter on the 11301 cant be measured with the 11301 and I don't see it (the jitter) on any of my other scopes though I can see the 100.3Mhz on the 3054 if I zoom way in.

The only way to get a clean trace out of the 11301 is to set the triggering right on the hairy upper or lower edge which isn't always correct trigger setting and the Autoset sets it higher or lower than zero when in AC and that produces a jittery trace.

As sson as I get some coffee in me I will run a sign wave into it from one of my generators to see if I can get a sine wave to lock.  the other isse is that it isn't completing the Enhanced Accuracy calibration and throwing an error "Main amplifier failed".  This could be related to the overall brightness of the signal as it uses photo diodes to align signals to the graticule lines in EA mode.

The EA problem could be overall calibration as well.  This showed up after a lot of messing around with the CRT alignment which is still inconsistent.  When the scope powers on, I have to reset the astig, brightness and focus for the character displays which should be stored in EEPROM which I think is rotten as it isnt holding.  The battery looks and tests fresh.  I've looked for a typical EEPROM to replace without luck.  According to the manual, a lot of the scope trace signals are set by a DAC on the scope logic board.  So the issue could be no calibration data on a scope that is more complex than the typical analog scope. 

I'll get better signals up a little later.

Thanks for sticking with me.

Jerry
 

Offline Johnny10

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #30 on: July 30, 2017, 04:50:15 pm »
On the DSA 602 I believe they self-calibrate isn't that the purpose of enhanced accuracy?
Not sure what happens with the 11301.

I have seen choppy captured signals on the 7000 series from the digitizer which are removed with the averaging function.
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Offline StillTrying

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #31 on: July 30, 2017, 05:40:55 pm »
As a random thought, are we sure it's not something to do with the 11301's Y delay line.
Does CH2 show the same ringing on fast edges.
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #32 on: July 30, 2017, 05:43:09 pm »
I drug my HP 8648C signal generator (not my best, but somewhat portable) down to the workshop and the results are below.  I am starting to wonder, and think that I am pretty sure, that the basic scope doesn't have a problem other than the calibration data.  If you look at the first trace it has the typical wide jitter (as I've been calling it) and the second is nice and crisp depending on how the trigger is set.  I took the same signal over to my 7603 and I can get an equivalent wide trace on it depending on trigger setting so maybe since I haven't been working with a analog scope in a while, this is normal?  Can someone with an analog scope see if you can get a trigger with a wide but locked trace?

It has other problems as the calibration is way off.  I might be able to fix that by just hand editing the calibration data text file as it is pretty self explanatory, instead of going through the PC based software routines.  As far as the Enhanced Accuracy (EA) this could be just an issue with a photodiode failing.  I read where it has 4 photo diodes (at least) in the corners and I think it uses them to time the signal against the graticule.  It could also be doing it with the touch screen detectors, no idea really, but during the process it puts a trace on the screen that moves back and forth over the graticule line.  I have a feeling that the focus is off for the test lines as they are really fat and that is why the scope isnt finding the dip when it passes over the graticule?  all speculation at this point.

Autoset brightness is off as though it completes successfully, there is no display until I crank up the brightness (which is a digital encoder).  I remember seeing a calibration routine for it.  But the Autoset displays the jittery, wide trace, not the sharper trace as when I tweak the calibration.

So now I'm not sure.  Most people would be happy with the lower trace.   I went down the trace brightness path as depending on the brightness setting you can get a wide trace that looks exactly like the jitter trace and since the scope had all kinds of focus and brightness issues when I got it, I thought it was all related to brightness.

So now I don't know what is going on.  Does it have a problem or is it all operator?  (I'm fine with the latter accusation).

If you play with the trigger on your analog scope, can you get a wide trace that is locked?  Is this typical?  Another thought, is since I am setting the trigger pretty precisely, is it possible it is on one side or the other of the jitter trace so it is only picking up some of the signal traces and not all of them?  Think of the setting only picking up the peak or trough of a wave where the overall envelope would be finer?  The trigger when in fine mode (little button by the knob) has about 3 - 4 settings where the trace is locked in a thinner display.  The display goes from real dim (locked and thin) to bright and thin to bright and wide depending on how the trigger is set. 

Thanks,

Jerry
 

Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #33 on: July 30, 2017, 05:45:20 pm »
All the channels have the same issue.  By the way, I was wondering what that loop of cable was inside the frame.  It looks like 100ft of shielded cable in a nice loop.  I figured it was a delay line of some type.  I was going to scavenge that as well as all the connectors if I decided to junk the scope.


 

Offline StillTrying

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #34 on: July 30, 2017, 06:09:28 pm »
On your last 2 photos the triggering levels seem to be +/-2.7 Divs, right on very the peaks of the sine wave, I'd expect an analogue or digital display to be jittery with the trigger there, because a very small amount of noise on the signal = a large difference in time.
I always try to put the trigger level on the fastest moving part of a waveform, = center for a sine to get the least jitter.
CML+  That took much longer than I thought it would.
 

Offline WastelandTek

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #35 on: July 30, 2017, 06:51:01 pm »
All the channels have the same issue.  By the way, I was wondering what that loop of cable was inside the frame.  It looks like 100ft of shielded cable in a nice loop.  I figured it was a delay line of some type.  I was going to scavenge that as well as all the connectors if I decided to junk the scope.

delay line
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #36 on: July 30, 2017, 07:14:21 pm »
So I think the autoset is setting the trigger closer to the peak vs where I set it is more in the signal so maybe it is ok.

I went back and tried to look at a slower signal and it is pretty tough to get it to trigger on a slow sine wave.  I think I can get it to trigger on a slow square wave because they have high freq. components.   On a slow sine wave it just jitters all over the place.

There's a 11301 for sale on ebay for a reasonable price and I am thinking of purchasing it.  I would really like to have a 400Mhz analog scope, been looking for one for a while.

Anyway, I wish they had schematics on this beast.  I just don't have enough doc to figure this out.
 

Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #37 on: July 30, 2017, 08:16:40 pm »
Well, I am officially giving up until by chance I either find another one or schematics.  I found that yes, I can get a decent display but when you lock it there, the counter reads garbage.  Hitting autoset, though there is no display, the counter reads the correct frequency.  I know there could be separate problems, could all be just calibration, but I think by playing with it more I am just optimizing around the base problem.

As far as calibration, you need very specialized signal normalizers; time markers and levelers; and a host of other equipment that I doubt even Tektronix has at this late date.  I was able to locate the calibration software and believe it or not, the proper rs232 cable.  I'm able to run tests, load and save the calibration, etc.  I tried loading the default factory calibration data but other than changing some measurements, it had no impact on the base triggering (or whatever) problem.

I'm going to keep an eye out for another one and use the amps in my DSA602 as planned.  It's too bad as I think these were pretty capable lab-grade bench scopes in their prime.

Thanks for all the pointers along the way.  By the way, I was thinking about posting some pictures from my DSA602 if anyone is interested.  If you don't know, that machine takes the same vertical amps.  The 602 is an interesting scope.  It seems to have pretty high precision capabilities for its age, lots of match functions including convolution, FFT functions with the inverse, filtering, etc.

Jerry
 

Offline StillTrying

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #38 on: July 30, 2017, 08:25:32 pm »
"Well, I am officially giving up until by chance I either find another one or schematics."

I wouldn't blame you, I hate it without schematics even on something much simpler than this.

According to the wiki the 11302 is nearly identical, no schematics in the manual, but some board diagrams.
http://w140.com/tekwiki/wiki/11302
CML+  That took much longer than I thought it would.
 

Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #39 on: July 30, 2017, 08:58:11 pm »
Yes, I have the 302 manual and used it prior to purchasing ($12) the 11301 service manual.  No real help.  I might go back and try that XY idea someone had on page 1 just for the heck of it.  I might also be able to sell the software in this one as it is the latest on 8 or so ROM chips.

Setting aside the calibration (which is tough to do) you would think I should be able to trace the signal into the functional blocks.  I guess I can pull the cable coming out of the delay line to see if it is stable.  That would be pretty easy.  This would tell me if the backplane (where the vertical amps are connected) is OK.  I've probed around on the Timebase board and at one point I thought I saw an issue with the 1T DOCXO as when I unplugged it, the horizontal ramp (but not the trace) became a lot more jittery.  Then I started thinking that if that was the case, then maybe the 1T feature is bad and I can just feed it a stable 10Mhz signal easy enough to see if that cleared up the issue.  But then I found that playing with the triggering gave me a decent trace.  But now I am pretty sure that the jitter reduced trace is related to tracing only a smaller number of repetitive waveforms resulting in a more stable main trace.  This would also reduce the counter value, which I am seeing, so that's when I decided to give up.

It's not like I need the beast but it is hard to put down!
 

Offline StillTrying

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Re: Tektronix 11301 - basic analog scope troubleshooting help needed
« Reply #40 on: July 30, 2017, 10:02:58 pm »
But now I am pretty sure that the jitter reduced trace is related to tracing only a smaller number of repetitive waveforms resulting in a more stable main trace.  This would also reduce the counter value, which I am seeing, so that's when I decided to give up.

That sounds very much like the trigger level is still on the very edge/peak of the waveform. Can you get the trigger DC coupled and near the center on the waveform. I can reproduce a fat 100kHz sine by triggering at its peaks.

Quote
It's not like I need the beast but it is hard to put down!

It would be nice to get working, don't buy another one!
« Last Edit: July 30, 2017, 10:04:35 pm by StillTrying »
CML+  That took much longer than I thought it would.
 

Online TerraHertz

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #41 on: July 30, 2017, 11:48:46 pm »
Could the trigger circuit have lost its DC path, leaving only some HF AC path? So the actual trigger comparator sees nothing but some spikes derived from fast edges in the signal?

That would result in symptoms like being able to (sort of) trigger solidly on square waves, but poorly on sine waves.

Not having the schematic is a real bitch.
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Offline cncjerry

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #42 on: July 30, 2017, 11:59:27 pm »
I'm trying to think on what side of the delay line is the trigger taken, according to the wiki, I think it is before the delay line:

Quote
The purpose of delay lines in oscilloscopes is to allow observation of the leading edge of the trigger event. In the vertical signal path, before the delay line, there is typically a trigger pick-off which supplies an undelayed copy of the vertical signal to the the trigger and sweep circuitry. Trigger and sweep circuitry need about 60ns to react when presented with the trigger event. Without a delay line, the trigger event would already have come and gone before the scope can trigger and sweep. By sending the input signal through a delay line, the scope will have triggered and begun sweeping by the time the trigger event emerges from the delay line. Thus, the trigger event is drawn on the screen where the operator can see it, photograph it, or record it by other means.

So if I look at the signal at the input to the coil of wire and maybe some of the amplifiers around there, maybe I can find something that looks funky?  The delay line is easy to find; the problem though is it is buried in the frame and I can't see the ends of the cable to get the color code.
 

Offline StillTrying

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Re: 11301 - basic analog scope troubleshooting help needed
« Reply #43 on: July 31, 2017, 02:22:31 am »
Yes, the trigger is before the Y delay lines, it gives the X timebase a few ns to start up and a few ns of trace before the actual triggered edge is drawn on screen.

I'm going by what's on the screen in the last 2 photos, the trigger says, "Main Trig= -2.74 acdiv",
"Main Trig= 0.1 div dc" would seem better for that displayed sine!

I suppose if an earth connection had come off one end of the delay lines it might cause that fast edge ringing on both channels, but I don't know much else about them.
CML+  That took much longer than I thought it would.
 


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