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Cannot find the difference between 2 signals
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batchas



Joined: Dec 15, 2013
Posts: 39
Location: switzerland

PostPosted: Sat Nov 14, 2015 4:18 am    Post subject: Cannot find the difference between 2 signals Reply with quote  Mark this post and the followings unread

I am comparing 2 signals. They look the same: peek-to-peek and spike.
1 is capable of looping the sequencer, 1 is not.

Do you have an idea what I should compare or how I should set the scope to enable me to visualize the difference so I can repair?
I mean there have to be a difference!

I had first to check signals which do work (the single step outputs which are able to loop the sequencer once plugged into a single step input) on both red and yellow probe. Like this I remarked that yellow y axis is a bit different than red y axis. So I put them on the same axis.
Cause in my precedent measurement before I aligned the axis, I thought the yellow signal was higher. But it’s not, it’s the same as the red if both are on the same y axis.
I hope you know what I mean.

Let me know if I can record something else, cause I'm totally stucked at the moment.

I have to say that worst case scenario, I know that I can send the module to Mark Verbos if I really cannot solve the problem by myself. Though I already repaired a couple of other issues and I'd like to technically learn in the process and also out of this bad luck experience, make it a positive one.


Here is a 2 mins video:
Link: https://www.youtube.com/watch?v=ruDgRo5hhQs


Oh yeah!
And I forgot to mention something.
When I take the output signal and connect it to a step input it does not work. This we know.
But if I touch the connection with my fingers, it is then capable of trigging/looping the sequencer!
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elmegil



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PostPosted: Sat Nov 14, 2015 3:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

The ripple on the yellow signal at "ground" makes me think you have a grounding problem. Touching changing the behavior could indicate that as well.
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batchas



Joined: Dec 15, 2013
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PostPosted: Sat Nov 14, 2015 4:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
The ripple on the yellow signal at "ground" makes me think you have a grounding problem. Touching changing the behavior could indicate that as well.

That's what I thought first (because of touching), but then like I show in the video I also checked with sending a "good" signal in yellow.
1:17 to 1:29
Then I change the signal going to the yellow probe. We see some zigzag at 1:30 cause I'm touching the probe (difficult while filming).
And I send a "good" signal in red and a "bad" in yellow.

What I mean is, the behavior on the yellow probe is the same wether I send a "good" signal or a "bad" one.

Or you see something different from 1:40 on?

I hope it is easy for you to explain.
I find it quite difficult myself here.
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batchas



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PostPosted: Sat Nov 14, 2015 4:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh.. you mean there is more ripple from 1:40 on than before?
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batchas



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PostPosted: Sat Nov 14, 2015 4:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have to make a new video with higher measurement.
Cause tbh I'm not sure it's not the same. We can't see very well.

All is banana on this module.
A grounding issue would mean that on these faulty steps, there's something wrong with the grounding on some of the components involved?
Is this what you mean?
And this is the reason why I cannot see a difference?
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elmegil



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PostPosted: Sat Nov 14, 2015 6:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

batchas wrote:
All is banana on this module.
A grounding issue would mean that on these faulty steps, there's something wrong with the grounding on some of the components involved?
Is this what you mean?
And this is the reason why I cannot see a difference?


Yes that is what I mean. My suspicion is that when you connect both to the scope you are probably sharing the scopes ground, and it looks OK, but if you connect it to something else that isn't getting a good ground reference it is "floating" and won't necessarily trigger correctly.
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batchas



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PostPosted: Sun Nov 15, 2015 1:38 am    Post subject: Reply with quote  Mark this post and the followings unread

I see... Thank you elmegil!
I was not aware of that.

Is there a method I should start with?

I googled "floating ground" and did not find info except discussions about high power sources in houses etc.

I know how to look for a positive or negative signal, I ignore how to look for a "floating" ground signal.
This is the next step in my life of DIYer life I guess!

Does it mean there is a ground connection missing at some point of the circuit?
When I take measures at all points and compare I do not see any difference.
It's a bit difficult to conceive atm, cause I imagine there is a 0v reference everywhere it should, as I can measure the level of a signal.
But as I understand, being able to measure has nothing to do with the floating ground. So floatig ground does not mean the 0v reference is missing.

I re-read your last comment.
You wrote "isn't getting a good ground"... I think I understand what floating ground means. You mean if I follow the 0v reference trace on the circuit, there must be a place where it does not go further or is connected to another disturbing signal.
Should I check between points on the ground trace to see how it "flows".
Or is there any other method?
Or I am totally wrong with my deductions?

Thinking out loud...
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batchas



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PostPosted: Sun Nov 15, 2015 1:42 am    Post subject: Reply with quote  Mark this post and the followings unread

batchas wrote:
there must be a place where it does not go further or is connected to another disturbing signal.

No it cannot be.

I would not be able to have same results between "right" and "wrong" signals when comparing the measurements.

Hmmm... Confused...
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batchas



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PostPosted: Sun Nov 15, 2015 1:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh... If I simply google "floating ground" instead, there are much more results which look interesting (I typed before "floating gorund how to repair").

I have to read that!
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batchas



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PostPosted: Sun Nov 15, 2015 1:53 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil.

you mean floating because you see that I put the level of the yellow y axis higher to coincide with the red y axis?

but if I take a "right" signal, there's no difference

aaargh. it's so difficult to explain.

I'll make a video.
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batchas



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PostPosted: Sun Nov 15, 2015 2:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Apparently I'm not the only one being confused.
http://forum.allaboutcircuits.com/threads/floating-vs-grounded.10670/

I'll make a quick video to clear up some details.

And I'm gonna compare in AC mode some points on the circuit with the same probe. Like this there's no confusion between y axis or whatever.

In each "wrong" output circuit there is 1 transistor which looks terrible. it's all SMD and a lot of the components don't look clean, but I'm going to test again at the transistor legs, in AC mode too.

I checked already the circuit for anything which might be in contact with the metallic layer, the ground layer which I see in the holes where the bananas where fixed. And I took anyway all bananas away to open the module, so there's no risk any banana leg is touching the metallic, grounded innerside of a hole.

I'm gonna stop writing and thinking out loud cause it's making it impossible to follow and to answer!
My bad!
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wackelpeter



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PostPosted: Sun Nov 15, 2015 3:41 am    Post subject: Reply with quote  Mark this post and the followings unread

If i understand you correct, the left input with the black does work and on the right the yellow one doesn't work... right?
If you put the the black one to the right Input and the yellow on the left, then which one doesn't work...
if it's still the same, left working and right not... then it's probably a grounding issue in the path of the right Input and it's components...
if they still still behave the same as mentioned first, then there is probably some grounding issue with the Output Signal with which you try to Loop the sequencer...
power off and if you have schematics check all Points that should go to ground with a DVM... maybe a bad solderpoint... also reasonably worth to check diodes if they are ok...

otherwise as you use bananas are both modules connected to the same power supply? if not try to get a ground from each and use a crocodile Clip to connect both grounds...

Floating means something like: frei herum fliegender ground... also irgendein Bauteil welches Kontakt zum Ground als Bezugspotential haben sollte hat diesen nicht... hängt quasi in der Luft...

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batchas



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PostPosted: Sun Nov 15, 2015 3:53 am    Post subject: Reply with quote  Mark this post and the followings unread

I am sorry not be clear to expose the issue.
Must be language (I'm not natively english speaking).

I have 1 step sequencer module which has 16 single outputs and 16 single inputs. So that when you connect for instance step out 11 to step in 2 it will loop.
This works on all steps, except step 13, 14, 15.

In my video und the upcoming one and in my comments here, I name all step which work the "right" / "good" / "working" steps.
I name the step 13 or 14 or 15 the "bad" / "wrong" / "non-working" steps.

On the scope I was trying to show that when I take measures between out 3 and out 15, I do not see the difference, I do not see any difference between "good" and "bad" so it makes it very difficult to repair.

I am uploading a new video. With, I hope clearer, information comparing measurements.
Zooming into the signal, using only the red probe to try to avoid more confusion.
Checking AC and DC, even if I know I work with DC signals (pulses).

The video will be up in a few mins.

THANX!!!!!!!!!! I appreciate your help here!!!!!!!!!
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wackelpeter



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PostPosted: Sun Nov 15, 2015 4:06 am    Post subject: Reply with quote  Mark this post and the followings unread

ok understand now (i think and hope i do Very Happy)

it was not your english... to me it wasn't clear that you used it's own step Outs for looping... first thought it was a external module... that could be my poor english too Very Happy
when you use the gate out of step 3 to 12 for example to step 2 in it Loops and when you use 13 to 15 to step 2 in it doesn't... correct?

are there any public links to it's schematic?

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batchas



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PostPosted: Sun Nov 15, 2015 4:16 am    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
when you use the gate out of step 3 to 12 for example to step 2 in it Loops and when you use 13 to 15 to step 2 in it doesn't... correct?

Abolutely.

wackelpeter wrote:
are there any public links to it's schematic?

I know about buchla 242 pulser schematics. My guess is that the 243v was inspired by the 242 but the circuit might be different.

http://rubidium.dyndns.org/~magnus/synths/companies/buchla/Buchla_2420_1_200.jpg

http://rubidium.dyndns.org/~magnus/synths/companies/buchla/Buchla_2420_2_200.jpg
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batchas



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PostPosted: Sun Nov 15, 2015 4:17 am    Post subject: Reply with quote  Mark this post and the followings unread

And the video is up:

https://www.youtube.com/watch?v=AwemZwwiJPs
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elmegil



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PostPosted: Sun Nov 15, 2015 8:38 am    Post subject: Reply with quote  Mark this post and the followings unread

I will catch up more later when I'm more awake, but what I mean by "floating" ground is that the ground for some section of the circuit is not connected to the ground for the rest of the circuit, or is connected but badly.

Let me digest what you've written and your new video and I will see if that suggests other ideas or a way to approach finding the problem.
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wackelpeter



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PostPosted: Sun Nov 15, 2015 9:16 am    Post subject: Reply with quote  Mark this post and the followings unread

had a look at the 242 schematics... buchla uses Flip-flop for each stage so as Elmegil already suggested there could be an ground issue on one of them... would check the 2 dual flip-flops for step 13-16... (i guess These dual flip-flops 4013 series perhaps)

that's maybe the simplest solution without having schematics is to compare the Pins of one that's working to one Output that is working... you could check one measuring the resistance between each Pin to ground on a working one, to see which ones shold be grounded... and then do the same procedure to the ones not working and compare them...
this can be all done without powering the module to avoid short cuts...

can you figure out what type of flip-flops are used?

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elmegil



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PostPosted: Sun Nov 15, 2015 9:35 am    Post subject: Reply with quote  Mark this post and the followings unread

So to refine my understanding of the problem:

When you connect outputs 13, 14, 15 to other steps inputs, you do not get the expected looping behavior, correct?

What behavior do you get instead?

If you connect other outputs to inputs for 13, 14, 15, do you get the expected looping?

Where were you touching that seemed to make them work correctly?

I agree that your video shows correct outputs from the "bad" steps. And since you are not moving the ground (I don't think you are anyway), that should rule out a straight-up "ground is not connected" problem. Edit: At least not with the output sections. Inputs, not sure.

I will look at the schematics you linked to and see if any additional ideas occur to me.
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gdavis



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PostPosted: Sun Nov 15, 2015 11:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Are you scoping the output while it's connected to the input? If not, try that. Don't bother with AC mode, just DC mode. Also try zooming way in on the time scale so you can see the rise time of the pulse.
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batchas



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PostPosted: Sun Nov 15, 2015 12:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
So to refine my understanding of the problem:
When you connect outputs 13, 14, 15 to other steps inputs, you do not get the expected looping behavior, correct?

Exactly. Just nothing happens.
And today not even by touching the conneciton would make it loop.

elmegil wrote:
What behavior do you get instead?

https://www.youtube.com/watch?v=ugrtVFKsBnY

elmegil wrote:
If you connect other outputs to inputs for 13, 14, 15, do you get the expected looping?

All single step inputs from 1 to 16 are working (number 12 was not working but I repaired it now).
It's only the output 13, 14, 15 which do not loop at any single step input.

elmegil wrote:
Where were you touching that seemed to make them work correctly?

I have a crocodile cable. It is connected to step out 15 and goes to step in 3 (for instance).
No looping at step 3.
When I touched the metallic crocodile connected to input 3, it then looped.
Today I was not able to replicate. Don't know why.

elmegil wrote:
I agree that your video shows correct outputs from the "bad" steps. And since you are not moving the ground (I don't think you are anyway), that should rule out a straight-up "ground is not connected" problem. Edit: At least not with the output sections. Inputs, not sure.

I concentrated on the outputs 13, 14, 15 cause the other step do loop when plug to any input.

elmegil wrote:
I will look at the schematics you linked to and see if any additional ideas occur to me.

Not sure the 243v is the same. I'm sorry I was not able to look at the circuit anymore (health problems).
I'll try tomorrow evening if I am able to.
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batchas



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PostPosted: Sun Nov 15, 2015 12:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

gdavis wrote:
Are you scoping the output while it's connected to the input?

Not in these videos.

gdavis wrote:
If not, try that. Don't bother with AC mode, just DC mode. Also try zooming way in on the time scale so you can see the rise time of the pulse.

Ok I'll try that!

I remember I saw only lines on the scope. Lines from all the 16 steps running. Was kind of strange to see this when scoping from the input where an output is connecting to.
But I'll make a video to show here and also do like you adviced.
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batchas



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PostPosted: Sun Nov 15, 2015 12:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
had a look at the 242 schematics... buchla uses Flip-flop for each stage so as Elmegil already suggested there could be an ground issue on one of them... would check the 2 dual flip-flops for step 13-16... (i guess These dual flip-flops 4013 series perhaps)

that's maybe the simplest solution without having schematics is to compare the Pins of one that's working to one Output that is working... you could check one measuring the resistance between each Pin to ground on a working one, to see which ones shold be grounded... and then do the same procedure to the ones not working and compare them...
this can be all done without powering the module to avoid short cuts...

can you figure out what type of flip-flops are used?

I did not check these cause they are SMDs and very very tiny (the legs are very near and they are placed in places difficult to access (because of the toggle switches). BUT, I'll check that to!!!
Cause I since then had the idea of putting a wire with a pin at both extremities to be able to go look in very tight places.

I hope I can do that tomorrow evening.
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batchas



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PostPosted: Tue Nov 17, 2015 3:48 am    Post subject: Reply with quote  Mark this post and the followings unread

I have to go work but I had time to make this video about inputs.
You'll see why I have difficulty to track the fault.

If I plug the probe, it will loop. It's like when I touched the connection with my hand (which by the way now by doing this does not make it loop anymore, but it's another story).

https://www.youtube.com/watch?v=2mCcOLp1DcE

I'll check the rest asap.
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wackelpeter



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PostPosted: Tue Nov 17, 2015 9:36 am    Post subject: Reply with quote  Mark this post and the followings unread

I still would say put one wire of your DVM to Ground of the module, then use the other wire via crocodile Clip and a small/thin wire to test the grounded Points of the chip's especially the flip-flop's... even smd chip's aren't that small that it'S impossible to position your probing wire...

as said before this measurements should be done without powering the module...

with 16 steps i would assume there are 8 identical chips on that board for the jk flip flop that in the original buchla schematic it was... that should be something including HEF, MC or CD4027 that's the Mos- jk flip-flop... in the orignal schematic it was a MC852 (5 times, hence only 10 steps)

These are the Chips where you should look at and compare between the working ones and the not working ones...

but as you said before all that smd components are a bit to tiny for you.. when you'll maybe find the wrong Thing/failure and it's a bad solder Point... you would have to solder it again...
If this is a bit to tiy for you and you don't have the ideal Tools for smd soldering it would be a reasonable idea to send it back and let Mark do the repair...

Speaking for myself i would not be very excited to solder smd components especially Chips as i would have to fear to destroy/overheat them... at least it's yor choice and your gentle hands you have to trust then... Wink

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