Author Topic: Project Yaigol: Fixing Rigol scope design problems.  (Read 79595 times)

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Online Bud

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #150 on: March 18, 2016, 03:08:41 pm »
Now that you've implemented the fixes, are you able to show any before/after screen captures from the scope itself which show the benefit of these changes?

I did not make before screen captures. The original goal was to fix the dysfunctional PLL and then it dragged into fixing its power regulator and then the other regulators. All that time the scope was face down on the bench and all I could only reach was the power button. Second - which some of people still do not seem to understand - this was about bad design practices per se and not about chasing improvements. Some people are OK to live in a house with the roof flapping in the breeze as long as the roof is not leaking. I would go and fix the roof. Third, if someone wants to do a compare he will have to design proper test cases first. One cant estimate improvements by just looking at the screen noise trace, all he will see will be noise generated in LMH6518 voltage control amplifier in the scope analog front-end which is so high that it even masks 8-bit ADC noise. And by the way, don't waste your time trying to measure the noise trace by enabling measurements/statistics - I found readings will depend on the position of the trace on the screen, which is another stupid "feature".


 
 

Online tautech

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #151 on: March 18, 2016, 05:10:10 pm »
Oh men, too much work attaching pictures...
Nice job on the Pt. 7 post, see you can do it.  :-+

Thanks for the tip, tautech, it was a bit messy at first but worked in the end.  :-+
Yep, pic compression is the key to getting lots of content into ones posts, glad you've got that sorted.

That you've got quality pics it the pdf's is great too for those wanting to have a good look.  ;)


Would you consider reworking the previous parts by way of "Modify" and put the pdf content into the body of each post?
Yeah, I know it's a bit of work, but man that'd really top off your great work and this thread.  8)
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Offline pa3bca

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #152 on: March 18, 2016, 08:15:11 pm »
A high res (well sort of) version of the landscape photo of the board from Part 4 with the oscillating regulators locations marked.
Had to look twice, almost missed it  :)

I am definitely going to open my 2072A en probe the PLL with an SA. (The SA is a Rigol 815, so I hope they are not in cahoots with each other...)
 

Offline pa3bca

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #153 on: March 18, 2016, 10:59:53 pm »
Well my January 2014 DS2072A looks not as bad as Bud's specimen.

Also I checked all the regulators and none of them oscillate. (checked with a 1074Z and the SA).
So what gives?  :-// :-//

The PLL however is not totally clean (not as it should be). But my measuring method is rather unprofessional as can be seen in the photo (I wanted a quick and dirty first impression). But I suspect that if I attach a balun to the diff output the spectrum should not get worse?
« Last Edit: March 18, 2016, 11:34:51 pm by pa3bca »
 

Offline exe

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #154 on: March 18, 2016, 11:02:37 pm »
Well my January 2014 DS2072A looks not as bad as Bud's specimen.

Could you please compare your part numbers (of LDO-s) with those on Bud's scope?
 

Offline pa3bca

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #155 on: March 18, 2016, 11:15:03 pm »
#2 on Bud's photo
« Last Edit: March 18, 2016, 11:26:22 pm by pa3bca »
 

Offline Emi

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #156 on: March 19, 2016, 01:46:01 am »
Hi. I'm "dicking" with coil loops  :)
Is this  tool  good enough  for  a  serious Job?
I would obtain the correct 3nH even  with thicker wire. .
http://www.eeweb.com/toolbox/loop-inductance/
Im really unable to handle such microbic #30  :palm:
« Last Edit: March 19, 2016, 01:56:34 am by Emi »
 

Online Bud

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #157 on: March 19, 2016, 01:40:13 pm »
Thanks folks for testing. Your PLLs are wobbly. Would you guys want to go ahead and make the PLL change and retest ?

How did you check for oscillation? You may need a spectrum analyzer on the rail.

Check the 6.3V rail for oscillation, it was strongest spot in my case, refer to the attached picture with the blue arrow pointing to the test location (rightmost terminal of the LDO)
 

Online Bud

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #158 on: March 19, 2016, 01:53:57 pm »
Is this  tool  good enough  for  a  serious Job?

I think it is, I tried with #30 thickness that I used, it produced same result.
 

Online Bud

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #159 on: March 19, 2016, 02:11:03 pm »
Well my January 2014 DS2072A looks not as bad as Bud's specimen.

Also I checked all the regulators and none of them oscillate. (checked with a 1074Z and the SA).
So what gives?  :-// :-//


That gives exactly this:



That Yaigol scope owners are at the mercy of which part suppler Yaigol used for their batch of oscilloscopes, the phase of the moon, or how much the Earth shakes when their neighbor's dog farts. Isn't this is what Quality Control is supposed to take care of.

For the LDO try locating the manufacturers datasheet and see if it spells requirements on output cap ESR. As to the PLL I think I showed sufficient evidence the design is incorrect.

[/quote]
 

Online Bud

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #160 on: March 19, 2016, 02:26:07 pm »
Would you consider reworking the previous parts by way of "Modify" and put the pdf content into the body of each post?

Will do when get some free time ...
 

Offline hendorog

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #161 on: March 19, 2016, 11:55:59 pm »
...Isn't this is what Quality Control is supposed to take care of.

Edit: Sorry I read something into your post that wasn't there - posting too late at night after a drinks is not a good idea.  :-[

No, it is not.

A well known saying in manufacturing used to be 'you can't test in quality'. Meaning depending on QC as the last line of defence will always fail eventually.
The only path to quality is to make it correctly. That is where the failure is, not QC.





« Last Edit: March 20, 2016, 05:29:50 am by hendorog »
 

Offline nctnico

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #162 on: March 20, 2016, 12:05:38 am »
I have prepared the oscilloscope MSO2072A again for a measurement.
With the E-field probe, I can see no oscillate. The peaks at 500 kHz are visible along the whole motherboard.
You are measuring the wrong pin! The middle pin/ tab is the output of the 1117 regulators. If they oscillate it is clear to see with a normal probe and usually at a frequency you could hear.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online wraper

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #163 on: March 20, 2016, 01:27:35 am »
Here the middle pin. Does not look like oscillate. Or do I measure wrong?
You have different LDO ICs, the same as in my oscilloscope which don't oscillate either.
 

Offline nctnico

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #164 on: March 20, 2016, 05:31:14 am »
I have prepared the oscilloscope MSO2072A again for a measurement.
With the E-field probe, I can see no oscillate. The peaks at 500 kHz are visible along the whole motherboard.
You are measuring the wrong pin! The middle pin/ tab is the output of the 1117 regulators. If they oscillate it is clear to see with a normal probe and usually at a frequency you could hear.
Here the middle pin. Does not look like oscillate. Or do I measure wrong?

This looks clean enough to me! All in all it starts to point towards a certain batch of oscilloscopes which might be affected.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Alex Eisenhut

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #165 on: March 20, 2016, 07:42:49 am »
Given the tremendous PCB real estate, Rigol could have saved 5 cents by using a printed inductor instead of a discrete inductor, seems to me. 3nH works out to about a 500 mils +- 50% on realistic stackups.

Am I naive?
 

Offline krivx

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #166 on: March 20, 2016, 09:50:21 am »
Given the tremendous PCB real estate, Rigol could have saved 5 cents by using a printed inductor instead of a discrete inductor, seems to me. 3nH works out to about a 500 mils +- 50% on realistic stackups.

Am I naive?

Possibly a printed inductor was considered to be too "baked in", there isn't much scope to change values later on.
 

Offline Alex Eisenhut

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #167 on: March 20, 2016, 10:29:57 am »
Given the tremendous PCB real estate, Rigol could have saved 5 cents by using a printed inductor instead of a discrete inductor, seems to me. 3nH works out to about a 500 mils +- 50% on realistic stackups.

Am I naive?

Possibly a printed inductor was considered to be too "baked in", there isn't much scope to change values later on.

Understood, but the PLL is not changing like the LDOs can, right? What's the second source for a ADF4360-7?
 

Offline krivx

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #168 on: March 21, 2016, 10:19:40 pm »
Given the tremendous PCB real estate, Rigol could have saved 5 cents by using a printed inductor instead of a discrete inductor, seems to me. 3nH works out to about a 500 mils +- 50% on realistic stackups.

Am I naive?

Possibly a printed inductor was considered to be too "baked in", there isn't much scope to change values later on.

Understood, but the PLL is not changing like the LDOs can, right? What's the second source for a ADF4360-7?

To be honest, I'm not familiar with the part. Do Analog make a range that use the same footprint? Moving to a cheaper or more available part in the same series is my first thought.
 

Online Bud

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #169 on: March 22, 2016, 06:10:46 pm »
I started populating Part 5, pls go to the first page of the thread to read.
It is again 3am in the morning... oh boy.

EDIT March 24:  Added JFET buffer info.
« Last Edit: March 24, 2016, 03:29:52 pm by Bud »
 

Offline tggzzz

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #170 on: March 22, 2016, 08:45:11 pm »
Part 5. Front End performance
This may be kind of stupid, why attenuate and then compensate by amplifying. My guess it is a compromise to have an input stage with wide range of V/Div settings.

I've just emerged from a Tek 465's front end. For comparison that consists of
  • two switchable attenuators (0/20dB, 0/40dB) in series, giving the 1/10/100/1000 steps
  • followed by cascode amplifiers with gain that can be reduced, giving the 1/2/5 steps
The 0dB+0dB+full gain -> 5mV/div, of course.
« Last Edit: March 22, 2016, 08:49:00 pm by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline nctnico

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #171 on: March 22, 2016, 09:17:57 pm »
So how come the total loss of the two attenuators is 48dB but we measured only 32dB at VGA output? Apparently the VGA compensates for the missing 16dB loss. This may be kind of stupid, why attenuate and then compensate by amplifying. My guess it is a compromise to have an input stage with wide range of V/Div settings.
This is actuallly very common in oscilloscope front-ends. The atttenuator also serves as an overvoltage protection circuit.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online Bud

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Online Bud

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #173 on: March 29, 2016, 03:01:05 pm »
How did I make these screenshots ?
 ::)

Bandwidth test


Raise/Fall time test




« Last Edit: March 29, 2016, 03:03:02 pm by Bud »
 
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Offline hendorog

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Re: Project Yaigol: Fixing Rigol scope design problems.
« Reply #174 on: March 29, 2016, 04:58:06 pm »
How did I make these screenshots ?

Two practical options come to mind:
Mirrored the R in some editing software, or changed the image in the firmware, recalculated the checksum and installed it.

The 2nd way is cooler, so I hope thats what you did :)

3rd option is mounting the installed filesystem, find the image and change it. That would get bonus points as I think no-one else has done that before...
 


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