Pendulum Frequency Counters CNT-90, CNT-91, PM6690, etc. - Page 1
Forum section: electronics / testgear

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 21, 2025, 05:53:38 pm
content: I received a Pendulum CNT-90XL today. It's in decent shape, but somebody stole the channel C option out of it. D'oh.I'm waiting for a price from Pendulum. This unit originally had the 40GHz module in it. I'm guessing it won't be a reasonable price to replace it.Anybody know of aftermarket / DIY prescalers for these?The stock fan is a loud 1606KL-04W-B30. Specs aren't that impressive, and I'm going to replace it with one of the Sunon fans I have. The MF40201V2-1000U-A99 is superior in all regards, and quieter, but I think I'll use the MF40201V3-1000U-G99 instead. The static pressure rating is slightly lower, but it's all open space with the fan in the back, so I don't think that should matter.Thanks,Josh

author: Rubo
author_rank: Regular Contributor
timestamp: July 21, 2025, 06:34:57 pm
content: They use same prescalers as PM6680, PM6681, PM6685.Cojotech used to make some nice upgrades, but not anymore.This is the only one I found -https://www.ebay.com/itm/262681428366

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 21, 2025, 06:49:02 pm
content: Quote from: Rubo on July 21, 2025, 06:34:57 pmThank you for confirming, I thought that might be the case. I emailed him about it already.Thanks,Josh

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 21, 2025, 09:46:30 pm
content: These things are pretty nice. Now I'm gonna see about adding a driver definition for TestController.

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 23, 2025, 07:39:18 pm
content: I posted the TestController driver in the TC thread (should be compatible with the clones/variants too) - though I will need to update it for the other mode options. It was pretty quick, as most of the functions are identical to the one I made for the 531XXA counters.Anyway, it's almost impossible to tell when I changed the Gate from 10ms to 1s:Thanks,Josh

author: Cyclotron
author_rank: Unknown
timestamp: July 25, 2025, 04:12:32 am
content: I blame you Josh...I just bought a broken PM6690 on the bay and will try to get it up and working since I have counter envy.

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 25, 2025, 04:42:44 pm
content: Quote from: Cyclotron on July 25, 2025, 04:12:32 amCongrats.Make a thread in the Repair section and share a link here so we can watch the progress.Thanks,Josh

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 28, 2025, 01:36:02 am
content: Here's the firmware updater including versions 1.28 and 1.32. The updater and 1.32 are what Pendulum sent me, apparently the version floating around the net are supposedly still the latest.Instructions:Code:Instructions for firmware upgrade of CNT-90============================================******************************************************************************************************************************************************* ****** WARNING ! WARNING! WARNING! WARNING! WARNING! WARNING! ****** ****** PLEASE CHECK CURRENTLY INSTALLED FIRMWARE IN CNT-90 FIRST! ****** ****** (CHECK IN THE USER OPTIONS - ABOUT MENU IN CNT-90) ****** ****** IF THE FIRMWARE VERSION ENDS WITH AN "s", e.g. "V1.12s", ****** NEVER DOWNGRADE TO A FIRMWARE VERSION LESS THAN INSTALLED! ****** ****** IF SO, THE CNT-90 MAY NOT BE LOADABLE AGAIN ("BRAIN DEAD") ****** AND NEED TO BE SHIPPED TO FACTORY FOR REPAIR ****** ****************************************************************************** Download the latest firmware (.hex file) and Loader.exe to your PC.* For upgrade via USB, make sure that NI-VISA 3.2 or later is installed with USB support.* Connect the CNT-90 to the GPIB or USB bus. NO OTHER instruments should be connected to the same bus.Firmware upgrade over USB works with firmware version V1.07 or above installed in the instrument.* Make sure that the proper interface is selected in CNT-90 (USER OPTIONS - INTERFACE)* Start the Loader.exe program* Press "Load" to open the firmware file.Follow the instructions on screen. The update is automatic.* After a successful update, the counter is reset (if previous firmware is V1.01 and above)* If the counter is not reset by the Loader program, turn the counter off and on when the update is complete.* NOTE 1: With some firmware revisions and GPIB cards the Loader gives an error message:"Counter I/O error. Loader shuting down" after the successful update.This is a fault of the Loader and not a problem with the upgrade process.* To remove the SRQ indicator on the front panel, which might be present in such cases,start a GPIB communication tool and send the command "*PSC 1" and power cycle the instrument.* NOTE 2: Some firmware revisions need a full power cycle to resume proper operation. If the instrument doesnot measure correctly after firmware upgrade, turn the instrument off and on to proper initialisethe hardware.* After the update, enter the calibration menu (password 62951413) and run "Calibrate internals"* The instrument is now upgraded and internally calibrated with the new firmware versionThanks,Josh

author: Cyclotron
author_rank: Unknown
timestamp: July 28, 2025, 01:45:54 am
content: Josh,This is fantastic. I was just looking for firmware updates. I've also found Tony Albus has a video on doing the firmware update.I'm going to take your advice and get my new Fluke PM6690 updated then start to do some testing. I bought it as broken but its starting to look less likely that it actually is.

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 28, 2025, 02:56:01 am
content: That's great! Updating the firmware will likely help. I had an older firmware to start with also, and it was terrible. More control, better stability, etc. after updating. For some weird reason, I couldn't save presets until after updating either. 🤷

author: BarrowBoy
author_rank: Contributor
timestamp: July 28, 2025, 06:41:51 am
content: Quote from: KungFuJosh on July 23, 2025, 07:39:18 pmI love this...We are the Australian representees for Pendulum. You should see the CNT- 100 series in action, never has there been such a counter/timer. Been in the sales game a while, know of Wayne Kerr / Philips / Fluke PM series. Was thinking about offering Mr Jones a 4 channel unit to review, would you be keen to see? Very low jitter, and "proof is in the pudding" as they say on the bench

author: Smokey
author_rank: Super Contributor
timestamp: July 28, 2025, 06:47:40 am
content: How short would a pendulum need to be to run at 40GHz? :⁠-⁠)(Length=1.55x10^-22m. Ha!)

author: Cyclotron
author_rank: Unknown
timestamp: July 28, 2025, 02:11:58 pm
content: Quote from: BarrowBoy on July 28, 2025, 06:41:51 am@BarrowBoyThat sounds cool! I do love that Pendulum is here in the community. I recently picked up a CNT-90. Having a company that supports the community, engages with us, and enables us to utilize older gear for our hobbies is very important. So much of the industry seems to be turning its back on enthusiasts, and that's going to lead to more sales for the companies that stick with us, for sure. I know it drives my buying decisions at work.

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 28, 2025, 03:25:10 pm
content: Quote from: BarrowBoy on July 28, 2025, 06:41:51 amYou should do that for sure, but also send me one so I can test it out and write a driver for similar work as the image you quoted.

author: Cyclotron
author_rank: Unknown
timestamp: July 28, 2025, 03:25:36 pm
content: I've started my repair thread for the PM6690 I just got in. Auto-Trigger doesn't appear to work.https://www.eevblog.com/forum/repair/fluke-pm6690pendulum-cnt-90-auto-trigger-not-working/msg5993303/#msg5993303

author: Grandchuck
author_rank: Super Contributor
timestamp: July 28, 2025, 03:43:07 pm
content: Quote from: KungFuJosh on July 28, 2025, 03:25:10 pmShameless!

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 28, 2025, 04:18:43 pm
content: Quote from: Grandchuck on July 28, 2025, 03:43:07 pmWhat value does shame bring us? Certainly not a fun counter to mess with.

author: pe1oxp
author_rank: Regular Contributor
timestamp: August 15, 2025, 03:57:27 pm
content: Is there a change log of the different firmware versions for the PM6690 and other brands?What are the additions/changes/corrections?In the posts of Tony i read about V1.28 and V1.32, my counter has V1.14 (2006)

author: KungFuJosh
author_rank: Super Contributor
timestamp: August 15, 2025, 04:36:19 pm
content: Quote from: pe1oxp on August 15, 2025, 03:57:27 pmI don't know about an official change log, but the older firmware sucks. The newest firmware runs better, and gives you better control over presets (save/recall).