Teardown & Repair of a Fluke PM6685R 4.5GHz Rubidium Frequency Counter - Page 1
Forum section: electronics / testgear

author: Hugoneus
author_rank: Frequent Contributor
timestamp: September 03, 2017, 05:11:14 am
content: You can watch the video here: [22 Minutes]youtu.be/_Rclt5ptc1UMore videos at The Signal Path:www.TheSignalPath.com

author: TiN
author_rank: Super Contributor
timestamp: September 03, 2017, 06:25:38 am
content: Repair curse strike again, too easy

author: Vgkid
author_rank: Super Contributor
timestamp: September 03, 2017, 06:55:34 am
content: Added to the queue for Monday.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: September 04, 2017, 03:49:28 am
content: Quote from: TiN on September 03, 2017, 06:25:38 amThere are a few repairs coming up which surely will not be easy. Fingers crossed!

author: Dr. Frank
author_rank: Super Contributor
timestamp: September 04, 2017, 10:46:35 am
content: Hi Shahriar,the repair was very interesting & good.OCXOs usually have about 1^-9 stability, whereas Rb are stable and can be trimmed to about 1^-11.So trimming an Rb at 1^-9 level, either against another Rb, or against a Cs clock or a GPSDO is not adequate at all.Maybe you better might demonstrate that adjustment process with proper phase drift monitoring, i.e. using a T.I. counter, which compares the phases of the DUT - Rb vs the reference-RB / GPSDO, at 1pps or 10MHz. I don't know, if that Philips counter is also capable ov resolving <= 1ns T.I., in this case it could be used.There's also a well known time-nuts monitor program, The TimeLab, by John Miles, KE5FX, which will collect the appropriate Allan Deviation data.That would make a nice video, I think.Frank

author: sarel.wagner
author_rank: Regular Contributor
timestamp: September 04, 2017, 11:34:45 am
content: @Dr. Frank, now that I would love to see....

author: 4thDoctorWhoFan
author_rank: Regular Contributor
timestamp: September 08, 2017, 12:10:32 am
content: Would it be possible for you to show a picture of the 10Mhz output waveform from the RFG-RB standard into a 50 ohm load?I'm asking because I want to verify that the unit I have is working properly. I actually have the RFG-M-RB version and the 10Mhz signal is more of a square wave than a sine wave.Thanks,Tony

author: Hugoneus
author_rank: Frequent Contributor
timestamp: September 08, 2017, 12:47:54 am
content: Quote from: 4thDoctorWhoFan on September 08, 2017, 12:10:32 amIt is definitely a square wave. I am thinking of getting a 10MHz filter to make a Sine output.

author: 4thDoctorWhoFan
author_rank: Regular Contributor
timestamp: September 08, 2017, 12:54:30 am
content: Thanks for the info.Could I ask you one more question regarding the RFG-RB?When you first apply power to the unit after it has been off, does the "fault" led light?I'm asking because on my unit, when I initially apply the 24V, the "fault" led lights up and remains lit until the rubidium locks. Then the "on" led lights and the "fault" led goes off. The "STBY" led never lights up. Just trying to figure out the normal operation of these units. Don't know if there is any major difference between the RFG-RB and the RFG-M-RB versions.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: September 08, 2017, 01:32:12 am
content: Quote from: 4thDoctorWhoFan on September 08, 2017, 12:54:30 amMine behaves the same way and I think that is normal. I never saw the standby go on. I think it can be configured through one of the ports.

author: 4thDoctorWhoFan
author_rank: Regular Contributor
timestamp: September 08, 2017, 01:46:25 am
content: Thank you Shahriar for your input. I feel much better knowing that my unit is probably behaving normally.Now I just need a Cesium reference to calibrate the rubidium reference. When does it ever end!

author: 2N3055
author_rank: Super Contributor
timestamp: September 08, 2017, 07:46:25 am
content: Manual states that standby light is on when unit is plugged in, but switched off with a button... It can be seen in the video @ 3:14Regards,Sinisa

author: 4thDoctorWhoFan
author_rank: Regular Contributor
timestamp: September 08, 2017, 10:37:04 am
content: We were taking about the operation of the external AT&T RFG-RB rubidium standard and not the Fluke PM6685.

author: 2N3055
author_rank: Super Contributor
timestamp: September 08, 2017, 12:54:57 pm
content: Quote from: 4thDoctorWhoFan on September 08, 2017, 10:37:04 amLOLMea Culpa... Please disregard the idjut in the room....On the more serious note, I guess it can be controlled from serial connector, maybe some external equipment can have have more than one unit in active/standby config (something similar with RFTG unit that has two oscillators...)