TNP #41 - Stanford Research SR620 Universal Time Interval Counter Teardown, Repair & Experiments
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- Опубликовано: 16 ноя 2023
- In this episode Shahriar repairs an SRS SR620 frequency interval counter where the magic smoke has escaped! The instrument does not power on and the teardown reveals a burnt resistor. The circuit examination shows a voltage regular for the 5V output which has a short circuit the the chassis. A simple repair and resistor replacement brings the unit back to life.
The performance of the internal OCXO is measured against a Rubidium oscillator and the unit is frequency calibrated. The XY output mode of the unit as well as its ability to measure propagation delays are also shown.
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Theres something satisfying about seeing an analog X,Y signal generating text next to the graphs.
This is really cool! The only thing I've seen even vaguely close is electronic music that's designed to produce images using x, y while also sounding - not terrible. It's interesting stuff. But this pure science application of it is quite cool.
I guess you needed me to bring one of my old analog scopes over to better see the XY output! ;-)
I can't believe you don't have a single analog scope. WOW
Yeah… Probably should get one. :)
A nice Tek 2465. Or maybe a Tek 2467 with MCP tube, to match the exclusive nature of the other equipment in the TSP lab 🤔
@@pa1wbu Yeah an analog Tek would do the job. Though I'm partial to the 465/475 being fully analog and super easy to source parts for.
Nice. I've been after one of these for years, never been lucky.
Looks like an SR650 Dual Channel Filter Repair coming soon!
Shariar, many thanks for sharing!
Anyhow, the SR620 is one of those legendary time-interval instruments for the 'Time-Nuts'. Its competitor from HP is the HP5370B (which qualifies myself as being a time-nuts. I'm lacking a Cs clock, though)
Both T.I. counters are able to resolve T.I. at around or below 20ps single shot, by using analog or digital time-interpolators. In the 70ties, such instruments were used (afaik) to measure the distance to the moon with ~ mm resolution, using LASER ranging methods, aiming at those 5 or 6 retroreflectors on the moon.
It would have been great to demonstrate its ps - T.I. capabilities, and its ability to make Allan Deviation measurements, i.e. stability measurements on oscillators by comparing your Rb vs. an ordinary XTAL, OCXO, GPSDO, and so on. "Noise Path" is the correct designator for such stability measurements, I guess.
John Miles', KE5FX 'TimeLab' program can directly interface to the SR620, and directly displays the stability statistics, from very short to very long time constants.
This high T.I. resolution also makes 'true', non-averaged 11 digits/s frequency measurements possible.
It would also be interesting, if you could explain this very special time interpolators schematic.
These are wonderful instruments, still cherished by time nuts! Time interval, Allan Deviation, reciprocal counting -- still a tremendous performer.
A great lab instrument! fortunate that the short did not create other damage.
I love the bit about the fan control. This shows the difference between dedication and "it's a job" when designing such things. I SO love your content!
I absolutely love these videos. I've learned so much stuff from them. But maybe more importantly, many of your videos have brought me to *understand* things that I've learned in the past, but didn't fully absorb before. Thank you!
Another excellent and educational video.
Thanks
Very interesting intrument, and such a neat trick of using an oscilloscope for displaying data
Very interesting...cheers!
very cool instrument, never thought that a f counter has this variety of applications.
Crazy stuff! I didn't know such an instrument existed. Micro-Hetz? OmG, the regular Joe's lab is happy with one second accuracy and GPSDO is luxury.
Thank you for showing us this, that XY mode is something else.
It's more precision than most people have access to, for sure. But the necessity depends on what you're doing. The whole reason atomic clocks exist (IE the "Rubidium source" we see in this video) is for some applications micro-hertz precision isn't enough. Anyway I'd still be happy owning one!
I love the big red LED display. It almost makes me want to build an outboard LED display for my 53230A’s.
Yeahhh just in time for my evening coffee, sweet 🤣 ( with the cat on my lap)
I love mine, although the GPIB interface seems to have some oddities that I haven't diagnosed, so I too have gone the HP 53310A for that use.
Shahriar, you really need a 2465B. 😀
or a 2467!
Wouldn't intensity scaling or a video trigger help show that output better on the digital scope?
Large unit - covered BENCH 8 all the way through to BENCH 2. :)
What would you think of doing a video looking at stability, accuracy, jitter and phase noise of different clock sources in your lab? Doing a comparison and contrast from worst to best in different areas. I'm guess this instrument might be able to help with some measurements
Would also LOVE to see a short tour of the guts of the machine. What parts are normy digital side and what if any interesting analogue circuits / parts are present
The clever use of the XY mode is interesting.
Though, would have been nice to see a picture of the backside of the unit, I suspect is as serial or IEEE488 or something given the connectors visible from within.
Also curious to what the coiled wires is for, seen to the right at 9:00
Yeah, he explains this at 1:30
@@andymouse I must have had a lapse in concentration to miss that. Thanks.
I saw an SR620 used as a prop in some sci-fi recently, though I’ve forgotten which. Some prop house apparently has one in inventory.
You could measure the speed of light (in air) right in your lab with that instrument!
SR620 introduced in 1988:
Formed in 1980, SRS is a unique, privately held corporation which designs and manufactures high performance test and measurement, signal recovery, and gas analysis instruments.
1982 SRS introduces its first product - the SR250 data acquisition system.
1985 Our first lock-in amplifier, the now venerable SR510.
1988 SRS heads into the engineering instrumentation market with the SR620 time interval counter.
1991 SRS introduces the DS345 30 MHz function generator. Direct digital synthesis is here.
1991 The SR760 FFT spectrum analyzer with 90 dB dynamic range and 100 kHz real-time bandwidth.
1993 The world's first DSP lock-in amplifier - the SR850.
1994 The DSP lock-in that's now an industry standard: the SR830
1998 SRS anounces the SR785 2 channel Dynamic Signal Analyzer, the ultimate 2-channel analyzer.
This would be a great instrument when creating delay lines for antenna arrays, like stacked VHF/UHF antennas in ham radio.
What do you get for a man who has everything? Apparently an analog oscilloscope :P Great episode as always.
Like those easy fixes makes up for the buggers! How do they measure mHz with short gate times?
Hey peeps, Shahriar needs someone to send him a nice Tek 2465.
What do you do with all this gear mate ? Planning to open a museum when you retire ?
Shahriar, where the heck did you find a schematic for a piece of SRS equipment? Did you just get lucky with Google or do you have a source? When I pulled an SR720 LCR meter out of e-waste at work and wanted to repair it, I emailed SRS and asked for a schematic. Their reply was, "We don't share schematics."
For this instrument, it is available on their website.
Wow, it looks like they've changed their policy! The schematic is now there for my SR720 LCR meter and my SR850 lock-in amplifier. I wouldn't have known this if not for your video, so thanks for that.
I use a EIP model 26b 15digit 26.5GHz frequency counter. Can you have a tear-down of this model? Mine is sat locked and good for 1/10 Hz.
What's happening with the coaxial cables @ 09:00? Are those delays lines or something?
Yes, delay lines.
That XY mode is pretty cool. Would have been even cooler if they supported a Z for trace luminance. Would something like this shift its time reference with thermal cycling (requiring recalibration)? Or is this instrument's crystal sufficiently aged that it wouldn't be a problem to cycle it on and off occasionally?
All crystals drift to some degree (or even jump 😱), but as long as the ovenized crystal is allowed to warm back up and stabilize, it should pick right back up to where it had last slowly drifted to.
@@ChrisSmith-tc4df Good to know, thank you!
When this device was issued?
That's really cool :) Would be interesting to know the theory of how they get way less than 1Hz resolution on a 1 second measurement. A normal counter that counts edges during 1 second would be limited to the 1Hz resolution
Huh? Because it measures million times per second?
i think you are confusing the lowest measurable frequency with resolution
The reciprocal counting technique
?
To clarify, if just counting edges, measuring 10000000.1Hz and 10000000.2 Hz would most likely just end up with the count of 10000000 counts during one second most of the times (sometimes gets one extra count). To increase the resolution, one must have bigger measurement window, for example 10 seconds, to get that extra digit of measurement, because then it would be 100000001 or 100000002 counts for those frequencies.
Using the reciprocal method means it has to be incredibly accurate to get to the fourth decimal of a 10MHz signal.
Using the recirpocal method of a scaled version of the input signal could probably make sense.
In any case, it is a challenging problem, and I'm curious how they solve it.
Which is it, Bench 8 or Bench 2?
Ha! There are two power bars, so each has a name.
You don't have an analogue scope! Well I suppose working at the frequencies that you do it might be a bit pointless.
The capacitor could be shorted, "...potentially speaking." No pun intended?
Ha!
I am pretty sure that in 1000 years, some Space Tik Tokers will look at devices like these in a museum in London and claim them to be proof that aliens built our computers and networks and the Las Vegas Sphere 😂
This xy mode is a bit strange. If they bothered to develop whole video subsystem, why wouldn't they take one step further and add normal vga or video output.
It uses a separate 8-bit Z-80 running at 8MHz for the graphics. It doesn’t have that much memory, so vector graphics with two inexpensive DAC’s allowed simple vector graphics to be added. A composite output would have required a RF modulator or an expensive monochrome monitor for this one purpose, while most benches have some kind of oscilloscope on hand. VGA didn’t exist yet.
@@ChrisSmith-tc4df interesting. Based on artifacts from the screen on the video I thought it has some kind normal graphics, not vector one. If it uses vector graphics then it makes sense to do it like this.
Use an analog scope with a Z input and you have a neat display. Analog scopes were common in the days this instrument was designed,
That XY mode was so unexpected and unnecessary that for a moment i thought i fell for an april fools joke
You have to remember this unit was made in mid-90s! Very useful to get additional information without having to write a bunch of interface code. :)
All that and no blanking. LOL 🤣
Isn't the unit designed to be ran with the cover on and that is why the thermistor was behind the fan? You have now moved it so that it does exactly what it was doing with the cover off. Fan comes on, thermistor sense and shuts it off cause it got the cold air coming in across the board and not the heat from the whole unit. What if it is the digital side closest to the fan there that actually produces the most heat? The fan no longer knows that. Got to have cover on it. P.S. I want one now just for the XY output.
Nearly all the heat from the unit is generated by the CML/ECL logic which is where I placed the sensor. The sensor is in an open area of the instrument and not directly beyond the fan. This has fixed all the issues with the fan startup problems.
@@Thesignalpath looked like it was kicking on and off fine to me. had the cover off.
No, it was not kicking anymore.
Thought it was going to be a RIFA ..
please don't take this as a personal critique - just in the context of a youtube video but your accent combined with the incredibly fast speaking (plus probably my bad hearing too) means I can't understand a lot of what you are saying. Trying to be constructive, I enjoy your vids when i can understand what you are saying 😂
Have you tried to listen to it at 0.75X? Some people say that it helps. :)
TIE THE THERMISTOR BETTER
OR
IT WILL SAG DOWN TO THE ELECTRONICS
It can’t reach all the way down. The cable is too short.