Adjusting the FY6800 Signal Generator (or Similar Models/Clones)
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- Опубліковано 19 лип 2024
- Six trim pots to rule offset, amplitude and symmetry on two channels …
↓↓↓ Complete description, time index and links below ↓↓↓
Warning: This video involves mains AC, which can cause serious injury or death!
One of the things I found annoying when reviewing that signal generator (link below) was the relatively large DC offset on both channels. And I knew from watching other peoples’ videos that there were indeed trim pots inside that thing.
Finally I came around to open it and had a go at those tiny SMD pots. First order of the day was to find out which trim pot does what. Adjusting the pots in a certain order made things easier. And you don’t necessarily need a scope for the job.
00:00 Intro - something I wanted to do for a long time
00:56 Opening - the enclosure
02:24 Inside - just a brief overview
03:08 Potentiometers - six of them, three for each channel
04:25 Identifying - what potentiometer does what
08:08 Calibrating - the DC offset, amplitude and symmetry
14:45 Multimeter - an alternative to using an oscilloscope
17:23 Wrap-up - quick summary and good bye
Tutorials: • Tutorials
FeelTech FY6800 60MHz Signal Generator / Counter Review: • FeelTech FY6800 60MHz ...
Poor Man’s “Bode Plot” with FY6800 Signal Generator and Oscilloscope: • Poor Man’s “Bode Plot”...
#robertssmorgasbord #tutorials #tutorial #calibration #adjustment - Наука та технологія
Hi Robert. Thanks for such useful info. I’ve just calibrated my 6900.
But one thing I’d like to point out. All three adjustments affect each other. For instance if you turn Amplitude or Symmetry pot it changes the Offset a bit. So my approach was to do it in several iterations. Set DC zero, go to sine adjust amplitude and symmetry. Go back to DC, check zero, +- 2, 4, 8 volts, adjust amplitude, symmetry and offset just a tiny bit (if values are just shifted adjust offset, if +- values are equal, but of wrong magnitude adjust amplitude, if negative values are almost correct but positives are wrong adjust symmetry). Go back to sine, check, adjust. When checking sine wave DVM in DC mode is very handy. For perfect symmetrical sine it should show 0 or almost 0 volts for any sine amplitude. Then back to DC. Repeat it several times.
Doing so I’ve managed to get very satisfactory results. It’s not great under 0.5v though, a bit shifted, but acceptable. Anyway I think it’s the best we can get from this cheap gear.
Regards,
Andrew
Thanks for detailed description of your calibration procedure! And sorry for the late reply - UA-cam notifications aren't what they used to be :-( Anyway, I totally missed that the amplitude pot influences the offset too - my bad. And I like your approach of using a DVM in DC mode to measure the offset of a sine wave.
One person also decided to turn the trimmers. At the very beginning, he replaced all resistances. Soldered multi-turn variable resistances. Then he twisted them without fear. Thanks for the video clip.
You're welcome and thank you very much for the info! That's actually a very good idea.
I would have named 'Amplitude' by the name of 'Attenuation' since the effect is decreasing in the clockwise direction.
Thanks for the walkthrough, I have a similar genny that I'm now pretty confident at least opening up to look at if it's the same. Wonderful content!
Thanks for the praise! And yes, 'attenuation' would have been a better fit. But then, the pot is really controlling the amplification of the output stage, isn't it? I guess one would have to reverse engineer the circuit to see if the pot attenuates the signal from the ADC (voltage divider) or controls the amplification of the output stage (e.g. is part of the OpAmp feedback) 😅
Hi Robert! Excellent! Your methodic approach is much appreciated. I Will now calibrate my FY6900. Thank you so much. Regards, RJM
You're welcome! And good luck calibrating your FY6900.
@@robertssmorgasbord ahh, 'adjusting' .... ;-)
I really enjoy calibration stuff , cheers!
As always, you're welcome!
An excellent calibration procedure. Thank you.
You're very welcome!
@@robertssmorgasbord He means 'adjustment' procedure ;-) (and yes, thank you.)
@@cheponis Well, I have to admit that 7 month ago the title of the video was "Calibrating ...". So I got it wrong too 😓 But fortunately ernesto pesto made me aware of my mistake a month ago and I changed the title to "Adjusting ...". And of course you're welcome 🙂
Good clear video! I noticed how “noisy” the scope trace was at ver low signal levels, I also have a digital scope and found it very irritating/confusing when checking audio circuits at low level/no signal condition.
Yup, when I got my first digital oscilloscope I first thought it was broken or I bought a heap of s... (Rigol DS1054Z). But it's just the name of the game and the reason digital oscilloscopes offer averaging a number of samples.
thank you so much for making this video. subscribed :)
You're very welcome! And thanks for subscribing!
Since dollar-for-dollar, a typical DVM is more accurate at measuring voltage than an Oscilloscope, I would suggest using only the DVM (and perhaps checking against the scope at the end for assurance). But rather than using RMS to measure the amplitude, why not just set the sine wave frequency to
You're absolutely right. Further down in the comments somebody has even suggested to use the DC "waveform" of the unit for calibration purposes. I guess there's more than one way to skin a cat and my way wasn't even the best ;-)
A tip before calibrating devices, is to first take measurements (and notes) of the resistance value that each pot is set.
That way, if all settings are messed up, you can always go back the way it was.
After calibrating you can add some Tipp-ex to secure each pot.
Thanks for the tip! That is indeed good practice. I also like the use of Tipp-ex to secure the potentiometers - who needs an expensive Loctite product to do that :-)
@@robertssmorgasbord , thinking outside the box :-) Tipp-ex can be used for many things in many branches besides office or home use. I used Tipp-ex back in the days when working as a car mecanic, to set mark points on the old distribution belt, and at the camshaft and crankshaft pulleys. After removing the old belt, i set at the same distance the 2 mark point on the new belt.
That way the distribution timing of the engine was always correct.
Tipp-ex can handle high temperature and can also be used as a anti-stick layer on the copper tip of a MIG/MAG welding pistol to prevent sparks from blocking the gas flow arround the welding arc.
Tipp-ex is almost the same as the white paint on traffic markings on streets.
@@BjornV78 My only unconventional use for Tipp-ex so far was touching up enclosure paint jobs or painting over screws :-) I didn't know it can handle high temperatures - that's really interesting and possibly most useful in the future.
I am not sure this is possible, but what about using this way: Set the generator to DC and offset to 0V, then (using precise voltmeter) set 0V on the output using Offset potentiometer. Then set generator to DC and offset to e.g. -5V, then using Amplitude potentiometer set exactly -5V on the output (I don't know if the output should be 50Ω loaded or not, results could differ), then set generator to DC and offset to e.g. +5V and set Symmetry potentiometer to obtain +5V on the output. And repeat this procedure two or more times, because the potetiometers could affect each other. If the offset is added to the signal on the digital side, then this should work and if this procedure works, it would be more precise, because DC voltmeters are often more precise than osciloscopes. I don't own this generator, so I am not able to test that.
On top of that. I am not sure whether using the -10V and +10V (or -5V and +5V) is ideal for calibrating that equiptment, because values are (in fact) not "binary aligned". I recently found this issue with some cheap chinese voltmeter, which displays 3½ decimal digits, but the last two digits increases/decreases in large steps e.g. I have 3.000V on the input, the voltmeter says 2.97V. Ok. But with 3.030V on the input, it still says 2.97V, the same happens at 3.040V, but at 3.050V it says 3.05V, which stays intact until the input voltage reach 3.130V. This looks like it displays voltage in 0.08V increments, which is kind of insane, but I found that situation is more complex, because the step is not exactly 0.08V, it is only rounded to 0.08V. I ran into serious problems trying to calibrate this voltmeter. IMO, the generator uses some DAC on it's output and despite the fact offset and other signal parameters can be set with 1mV accurancy, I am not sure the DAC is able to output it with this accurancy, its step could be much higher than 1mV and not decimal, which makes selecting right calibrating voltage crucial. Maybe you should try to determine the DA converter step first, then (using the determined step) compute some binary aligned calibration values and then, after that all, calibrate to theese values. It should return better results. Maybe the device itself has some calibration menu.
Hi Niki, thank you very much for that very well thought-out calibration procedure. Of course, using the DC output mode of the unit! Can't really say why I haven't considered that, but I didn't. I also like the reasoning about using binary "even" values for the calibration to avoid digitalization errors. Well, to answer your leading question: Yes, it's absolutely possible to do it this way. In fact, it might as well be the better way. Thanks again for your contribution.
I've got wondering why my HP3400A is measure not correct as shown in FY6900's LCD displays..I got answer that an Oscliioscope and HP3400 were shown same measurment value. This VDO is really help me calibrate this FY6900..Thank you :D
You're welcome :-)
Also Robert, did you see while turning the potentiometers if there is way to do unipolar at the sacrifice of the total supply excursion of course (i.e.to DC offset the output for example 0 volt to 10 volts) for special purpose like feeding a unipolar circuit. A small dautherboard could then be put in place with a second set of pots and a switch in the back to operate this function. Thank you. Regards, RJM.
Hi René-Jean, I don't think that will work - at least it wouldn't with my unit. The range you can set the DC offset with those pots is simply too small.
Best Regards
Robert
Hi Robert! Thank you very much for your reply. Best regards, RJM
@@rene-jeanmercier6517 I think the main controls of the unit allow you to set large dc offsets- in the previous video for example there was a waveform listed as "CMOS" which is gonna be a 0-5v square wave for instance.
Specs state that you can offset 10v under 20mhz and 2.5v over 20mhz - half the maximum voltage peak to peak at those frequencies, so you can make it double ended.
Why is the maximum peak to peak voltage less at higher frequencies?
Idk, at a guess it needs to do some kind of multiplexing to get that higher frequency so has to reduce the vertical range to compensate? Or maybe a slew rate Limitation?
(Edit judging by the fact that it specifies a 7ns rise time...but only at 5vpp it's not unbelievable to state that it is in fact a slew rate limitation.)
Edit edit: yup looked again and it states an 18ns rise/fall time for a large transition, which is going to hard limit it to at most 25mhz at full range
Dylan. Thank you very much for this second reflection on the capabilities of the instrument. This is too kind of you ! Regards, RJM
My FT 6600 was dead nuts on right out of the box! Thanks anyways.
You're welcome! And very lucky ;-)
you are VERY VERY lucky....
Can I also calibrate the counter? (Without 10MHz reference)
Nope. You don't get anything better than the crystal on the board as a time base.
@@robertssmorgasbord The on-board crystal is TERRIBLE for frequency stability. I have check it versus two GPS disciplined clocks.
@@cheponis Yup, that thing is not the most stable frequency wise. But I guess you really can't expect an TXCO or OXCO in a Chinese box for that price. Besides, before putting in an TXCO/OXCO they should probably revamp the output stage first. See "FeelTech FY6800 60MHz Signal Generator Review Addendum II (Output Stage)" ua-cam.com/video/u6zQM3S556A/v-deo.html
Cool stuff! An interesting mod could be to change that trimmers for multi-turn ones, uh?
I had the same thought when fumbling around with those tiny things :-D
Unfortunately, at least wIth mine (FY6900), there's a significant variation in the calibration when the output voltage is varied to cross over the 2 boundaries of the 3 scales (first boudary is 0.5000V - 0.5001V, second is 5.0000V - 5.0001V, hear the relay clicks). This makes adjusting the instrument over the full scale much more complicated and resulting in a compromise. For instance, in my case, 0.5000V actually outputs higher amplitude than 0.5001V, and apparently there's nothing to do about it, since it's due to the fixed resisors which are used to scale the voltage by the relays. Also the output capacitance appears to vary at scale crossings.
Kudos to you! I've got nothing to add to your very thorough comment. Basically you can calibrate the unit only for one of the three output ranges properly. I should have mentioned that in the video. My bad!
@@robertssmorgasbord Thank you, but it's only because I had the bad idea to touch those trimmers, and then had to spend an entire afternoon in trying to readjust at best that instrument...
Brasil 👀🖒
😃
I don't mean to be picking on your good work. What you are doing is not calibrating. It is adjusting. Calibration means measuring and comparing something against a traceable standard and recording the difference with the degree of uncertainty. Using the word calibrate when you really mean adjusting, in this way adds to much confusion amongst new people watching this video. At no point in this video did you show that you took any measurements and there was no indication that you were using any reference standards. Calibration does not imply that an adjustment has been or needs to be made. Take for instance a Gauge Block. This can be calibrated but can't be adjusted without some intervention. Choose your words carefully and adjust the title of your video to avoid confusion.
Yup, you're absolutely right, my bad! Though in a wider sense you could view the used multimeter and oscilloscope as calibration standards (known accuracy according to manufacturer specification) Google (Android 12L) 😉 But then, I didn't record/specify the outcome of the measurements, so it's still just adjusting. BTW I already changed the title to "Adjusting ...".
The reason I am picky on this subject is that I recently sent my Keithley 2100 in for calibration after repairing it myself. It was passing diagnostic self test so I just wanted to know if it was within spec or how far out it was. I got an email back some weeks later from the people who now own Keithley "The Keithley 2100 has failed calibration and required repairs to rectify. We have quoted for repair and calibration". The quote was for $1827.10. I was astounded. How can a meter that was functioning at the time I sent it, fail calibration?
In a panic I ordered a new DMM6500 and declined to have them repair the 2100. I got the 2100 back in working order and there was a calibration certificate attached. So someone had confused calibration with adjustment and instead of saying the 2100 was out of adjustment range now assumed that me asking for calibration also meant adjustment. So the whole exercise cost me $430 to get my 2100 meter back apparently uncalibrated and another $1800 for an ex demo unit. Very costly misunderstanding. I cringe when I hear somebody using the term calibrating when they are turning a potentiometer. The term is used far too loosely without any understanding of what it represents. Sorry for the lengthy reply but I felt I had to put my comment into some perspective. Thanks for your speedy reply and for a great educational and entertaining you-tube channel.😀
@@ernestopesto2874 No worries and no need to explain yourself. You were absolutely right in the first place. I just did *adjust* the thing, not *calibrate* it. However, yours is a very interesting story and really explains why you are so sensitive to the misuse of the word *calibration*. Anyway, regarding your ordeal: You can never have enough DMMs (bench or handheld). So having two working ones now is a plus - albeit a very expensive one.
@@robertssmorgasbord Yes, when you have 2 DMMs, then probably at least 1 of them is correct some of the time.... (This means you need 3 DMMs !!! and vote...)
@@cheponis Yeah, that's always the safest way to do it: Take three measurements and take the two that agree 🙂 BTW that's how most of the critical avionics work on commercial planes, e.g. three sensors for airspeed.
Смелый человек. Подстроечные сопротивления невысокого качества. можно совсем потерять все настройки :).
Не храбрый, а просто отчаянный ;-) Нулевое смещение сводило меня с ума. [Google translation]
Not brave, just desperate ;-) The zero offset drove me crazy. [English original]
(Прохожий wrote "A brave man. Trimmers of low quality. you can completely lose all settings :)" [Google translation])