TSP #106 - Teardown & Repair of a Fluke PM6685R 4.5GHz Rubidium Frequency Counter

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.

The Signal Path

[ChipGuy]

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.

[PapasDino]

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.

[Drew-Dastardly]

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.

[laser-on-off]

Thank you for the video, I really enjoy watching the repairs !
Greetings from France.

[caulktel]

Great video, I'm still drooling over that Fluke PM6685R.

[yaghiyahbrenner]

The new sound makes a huge difference even the MIC's AGC is noticeable. :)

[rwils]

Great video as always. Lol I do get jealous at all those nice instruments.

[allesklarklaus]

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?

[samfedorka]

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.

[FesixGermany]

My boyfriend saw such a unit with the 2.7GHz option on ebay, we watched this video and decided to buy it.

[xDevscom_EE]

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? :)

[SidneyCritic]

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.

[kmgy]

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!)

[HevyFilms]

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...

[davebeerman]

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!

[proluxelectronics]

Would the 10MHz sine output on the Agilent measure differently to it's square output?

[wilfredswinkels]

the stupid thing with these counters is, that you're always counting zero's because they didn't add the extra comma's.

[vaualbus]

We wanna the the other video😁😁.
By the way good video.

[andregrouche]

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 :)

[kmgy]

Can you take the Rubidium standard as an output and distribute to your other instrumentation?