Pendulum CNT-90 (Fluke PM6690) help needed - Page 1
Forum section: electronics / repair

author: BetoSaba
author_rank: Newbie
timestamp: August 05, 2019, 01:23:44 pm
content: Hi guysI've bought a used CNT-90 from e-bay.Really liked the counter but...It came with standard (ucxo) timebase.For a counter with 12 (14) digits, it's no good.So, I've bought a Morion MV 197, removed the original ucxo and installed the MV 197.Then I've used the configuration software available at KO4BB site to reconfigure the counter.It changed the ID (now it's a Fluke PM6690), but the ocxo is now recognized.The problem is: I can't calibrate the MV 197!Using the User Options -> Calibrate -> Timebase -> 10MHz -> Start gave me "Impossible to calibrate timebase. Bad reference signal?"Any ideas?Other problem: FW version is 1.09. I've found 1.28 at Spectracom site (It's a Pendulum app). I've tried to apply the new FW via GPIB bus. It uploads the new FW and apply almost to the end, then, without any error message, undo all and revert to the original 1.09.Anyone has any idea?Thanks

author: Theboel
author_rank: Frequent Contributor
timestamp: August 05, 2019, 02:15:58 pm
content: Hi BetoSaba,I update my CNT-90 use USB connection.if I remember correctly I do not found any problem except when its finished (no warning if its finished only a full bar graph) You need to restart the counter and new FW working perfectly.

author: ArthurDent
author_rank: Super Contributor
timestamp: August 05, 2019, 02:46:45 pm
content: The reason a lot of high end counters and other high end pieces of time equipment don't have a high stability timebase is the added cost isn't worth it. So many people who use these counters also use a house frequency standard that supplies the standard frequency to all equipment in their lab.I have a couple of CNT-80 and CNT-81 counters and they came with standard timebases. I did install my own Rb timebase in one but found that I still used the GPSDO 10Mhz almost all of the time. It is the same with my HP53132A that came with a high stability timebase, I still use the GPSDO for that as well. The advantage of no warm-up and not leaving the instrument on 24/7 is what I consider a big plus.Gerry Sweeney had designed a replacement high stability timebase for the HP53132A series of counters to allow the autocal to work properly and the daughter board with the OCXO had to have some added circuitry to allow the autocal to work. The link below may be of interest to you on what he did with the HP counters. I'm not familiar with the innards of the CNT-90 but did you copy the timebase board and any necessary added circuitry or did you just add an OCXO? There appears to be something your firmware is looking for that prevents the added OCXO from being recognized.https://gerrysweeney.com/update-diy-hpagilent-53131a-010-high-stability-timebase-option-pcbs-available/

author: BetoSaba
author_rank: Newbie
timestamp: August 05, 2019, 03:07:11 pm
content: Hi ArthurThe board of the CNT-90 is already prepared to just install the ocxo (and reconfigure the counter).You just have to remove the standard ucxo nd install the new ocxo (12 V 36x27mm).I also have rb and gpsdo, but I want to have the flexibility to move the counter in "field operations".I have a PM6885R and just calibrated the rb with a Thunderbolt that is running for months with a well placed antenna.I was able to obtain 10.000,000,000,000 MHz after 2 hours of measurement (7200 counts, 1 count per second).I my lab I am using the PM6685R as the source for all 10 MHZ refs that I have (other counters, generator, etc).But is unpractical for field.Thank you for your reply.

author: BetoSaba
author_rank: Newbie
timestamp: August 05, 2019, 08:42:50 pm
content: Hi TheobelI've tried the update with USB connection and... It worked!Thank you very much!But I still can't calibrate my ocxo. Same error as described before.

author: MaxR
author_rank: Contributor
timestamp: February 06, 2020, 06:22:25 pm
content: Hi BetoSaba,do you still have thi issue with timebase calibration?Maybe i could help.Please send me or post photo of TOP side of the main board and screen with About menu.

author: testpoint1
author_rank: Frequent Contributor
timestamp: February 07, 2020, 02:44:58 am
content: Hi, if you use PM6685, use a OCXO also OK , but the warming time may need 1 hour, if you use PM6690 PM6691, you must use a Rubidium clock or Cesium clock.

author: liszt955
author_rank: Newbie
timestamp: July 23, 2024, 01:13:34 am
content: HI,BetoSaba，Have you resolved your issue?I'm encountering the same problem. If it's been resolved, how was it solved?I would be very grateful for your reply.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 23, 2024, 01:37:51 am
content: you should send a pm instead, hes not been here since 2022 you may wait a long time ...