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- Опубліковано 6 вер 2024
- In this episode Shahriar repair a Fluke PM6685R Rubidium Frequency Counter. The instrument shows highly unstable results and produces high-pitch noise when powered on. The high-frequency noises point to a problem with the DC-DC converter circuit in the power supply module. A close examination points to degraded capacitors. After all capacitors have been replaced, the noise issue is resolved. The instrument's performance is then verified and calibrated against an external Rubidium reference. The agreement between the units is better than 10ppb.
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Well...the man who has a watch knows what time it is...the man who has two watches isn't sure! Nice fix Shariar...I use both a Rb and GPSDO reference here and it's interesting to compare them on a scope.
Since last weekend I appreciate those so called "broring bad caps" repairs much more, since I had to spend the entire day hunting down a broken Altera FPGA that got a screwed up PLL and/or internal R/C oscillator.
I had a giggle at you not realising the 10 x 10^6 Hz indicator was being used instead of 10 MHz. I watched your older TSP #72 for the PM6680B and @ 41:30 in noticed you had it in 1/f mode and it was displaying 100 x 10^-9 s (100 nanoseconds) which of course is 10 MHz too.
At least it appears to use engineering notation. I guess they didn't have enough LCD space for all the symbols. Thankfully they didn't go for scientific notation, that always confuses me.
Anyway thanks for another great vid. I love repair videos.
Great video as always. Lol I do get jealous at all those nice instruments.
@ R Wils I concur. He has the most beautiful instruments I have ever seen in my lifetime. Most of my instruments are 20 to 50 years old!
Thank you for the video, I really enjoy watching the repairs !
Greetings from France.
Instablaster
Great video, I'm still drooling over that Fluke PM6685R.
The new sound makes a huge difference even the MIC's AGC is noticeable. :)
Sorry for the late comment but that last Agilent unit was probably warming up still. It's output was slowly getting closer to 10MHz at about 10 or so mHz per second. Maybe it wasn't so bad after beeing left on for an hour?
Repair again too easy for you :). Now only need to calibrate the calibrator with GPSDO. Perhaps a good idea for video how to match two unknown frequency sources to ppb accuracy? :)
Did you consider modifying the fan such that it activates for the Rubidium PSU?
One caution to newbies: Always good to fully discharge electrolytic capacitors before connecting them to an ESR tester (or anything else!)
Haha....
k1mgy, if there is no problem that you're trying to fix, why would you change how the device operates? Obviously the engineer who designed the device in the first place didn't calculate the fan was needed when the device is in standby.
My boyfriend saw such a unit with the 2.7GHz option on ebay, we watched this video and decided to buy it.
the stupid thing with these counters is, that you're always counting zero's because they didn't add the extra comma's.
There's a little transistor heatsink in the Rb power supply that looks like the open hardware logo and that's all I can think of when I see it.
These are the best !
You must be lucky getting mainly PS fixes because FeedbackLoop mainly gets MB stuff. It was still good to watch because it had those oscillator comparisons. Now you just have to "B" it.
I saw Your Efratom RFG-RB. I have the same device, but I have no Informations about the SUB-D Pins. Do You have Informations about this or any other Informations? I cant find them in the net...
Best video ever, thank you sharing
Thank you. Another great video.
Great video!
Good repair, but calibration not so good for Rb reference.
Rb has to be calibrated to about 10^-11 vs. GPSDO; that requires very different method, than you have shown.
Either a longer scale frequency counter, or a T.I. counter with > 1h phase comparison is required.
Yes, you are right. I have to get a GPS disciplined source. :)
Great video. Thanks.
Would the 10MHz sine output on the Agilent measure differently to it's square output?
Power supply repairs are only boring because the number of failure modes tends to be very small. DC/DC converter design is interesting, but almost none of the design considerations are important when figuring out what to fix. And since most are built with monolithic controller ICs (or even regulators with a built-in switching transistor) there's no way to figure out what went wrong in the rare case that the chip is the problem. You'll never have an error where you replace the internal oscillator of the regulator IC or find a problem with the error amplifier.
Two other things: First, I'd love if you kept a list of what equipment you have in the lab on the blog site. It would be fun to know, and trying to go through all your videos and read part numbers would be very tedious. Second and more importantly the "about" page on thesignalpath.com really ought to have a separate entry for the cat. I've forgotten his name which is clearly horrible.
The cable you mention at 5:14 that carries the 10MHz signal from the rubidium clock has me a little confused. Shouldn't it be a coax, or at least shielded? 10MHz isn't _too_ fast, but still coax worthy, no? Perhaps I did not understand or misunderstood something? Anyway, thanks for another great video!
It will go through some PLL on the main board anyway so doesn't really matter.
Nice video
HI after 2 hours my PM6685R stop functioning with a "no signal" display. At this time when i test the sub menu, the logic seems to be faulty. One hour later after power off etherything is working fine again. Do you have any suggestion on the way to diagnose and fix the problem ? Kind regards from Normandy :)
👍👍
We wanna the the other video😁😁.
By the way good video.
Awesome video. I can't stop watching all these repair videos now I've found this channel! Most of the stuff is way over my head though as I am still fairly new to hobby electronics on the scale of things. Why do you often test with low Z mode as opposed to normal V mode? Can you test right up to 1000 V on low Z mode also?
Terry 01 Modern (well, kinda modern) DMMs have a very high input impedance of over 10Megaohms if you test in regular mode. That means it could be just some leakage or EMI causing a voltage reading, so called Ghost voltages that disappear as soon as you put some very tiny load on it. The LowZ mode is basically a 100k or so resistor in parallel with the DMM input so you don't get these ghost voltages. Most good Bench multimeters even have such a high input impedance that if you leave the probes unconnected to the input it will still measure some voltage, sometimes even climbing up to 5V or more.
Can you take the Rubidium standard as an output and distribute to your other instrumentation?
Not sure about this specific unit but in general, yes. I took a look at the PM6685 (non-R) that I have here in the lab and it does have a 10Mhz output. I built a distribution board that distributes the 10mhz signal from my home built standard to the other instruments in my lab.
Holy terror, an ATOMIC CLOCK?
Well, this is a first for me.
Please let me know your secret for buying faulty equipment. Almost EVERYTHING I buy (even 'working') seems to have multiple complex issues. Never have I had a simple power supply fix. Rant Rant Rant! Happy for you tho.
How do you understand the working just by looking into the circuit ! You are an amazing Engineer and inspiration to budding engineer's like me , I have a request for you can you make videos (Tutorial's ) on designing advance electronics project right from scratch like from Idea ,creating a circuit ,Picking right components,building it because I did't find any videos that follows this kind of a workflow
*drool* I mean, yeah, nice, whatever...