Kvarz CH1-76 Passive Maser repair - Page 1
Forum section: electronics / general

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: June 23, 2019, 03:17:00 pm
content: Hi!I've had several queries on the status of the repair so will add to this post as I progress. The unit (120 pounds unboxed!) arrived OK. The front door had come off its hinge and the rear cover over the dissociator got bent a bit. No problem fixing them both.Got it up on the bench with help from a friend and removed the covers. PIX shows the top which is called the AFC assembly that consists of A1 thru A9. The bottom PIX shows lots of perforated modules, these are power supplies. Also the 3 flat boxes which are the oven control hydrogen control and RF mixer.Swapped out the Russian multi-pin external DC connector so I could power it from a bench supply. Powered up and the ion pump current dropped down as expected but the ion pump voltage does not read, something to troubleshoot later. The high frequency oscillator (HFO) for the Hydrogen discharge lit fine so there is still Hydrogen in the supply.The I.F. output jack on the rear panel just showed noise so went looking for the cause. Found a bad connection on one of the coax jacks. Fixed that and got some I.F.! Maser action is discernable but weak. Was able to get it to lock and made the attached Allan Deviation plot. Does not quite meet specs but is about as good a medium performing HP5065A but without the drift. Also this beats the specs for an HP 5071A! The Xtal and cavity AFC switches don’t act quite right but will work on that later.The I.F. showed a modulation frequency of 5 Khz vice the correct 12.5Khz! After some head scratching found that someone had modified it. After a couple tries removed all the 5 kHz mods and returned it back to 12.5 kHz. Working on optimizing the settings and then will try another AD plot.Well the AD plot is a bit worse with the 12.5KHz modulation. I'll need to optimize the hydrogen flow and the frequency of the HFO discharge oscillator. It's reading 89.6 MHz and the manual states between 100-120 MHz . Then see if the AD improves. Also found another undocumented mod inside the integrator module while trying to figure out why the AFC switches are acting funny. Can't quite make sense of what they were trying to do. The two op amps used for the XTAL and CAVITY integrators won't zero using their pots?More will follow.Cheers,Corby

author: edpalmer42
author_rank: Super Contributor
timestamp: June 23, 2019, 11:18:14 pm
content: After some digging, I was only able to find a datasheet on this maser. Is there a manual available for this or any maser? Or maybe a good description of the principles of operation?What are you using to measure this? Something like a Timepod is way out of reach for a hobbyist like me.Ed

author: TiN
author_rank: Super Contributor
timestamp: June 24, 2019, 12:04:57 am
content: Cool project. If you need translation for pieces from russian, will be happy to help.More photos would be great too, never seen insides of such box.

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: June 24, 2019, 12:56:27 am
content: Ed,On Tom Van Baaks leapsecond.com website there is a copy of the ops and maintenance manuals for the EFOS 2 active Maser.http://www.leapsecond.com/museum/efos/Gives you a good idea of the workings of a Maser.I had that maser at my place for 11 years and it just went to its new home in April.The Kvarz is a passive Maser that has a smaller cavity with a lower Q so it will not oscillate. It will however provide Maser gain and this is used to provide frequency discriminator action that will lock the Quartz oscillator to the Maser line. The Kvarz also has automatic cavity tuning which eliminates drift.I'll look into seeing if I can have someone post the operator manual which includes the theory of operation for most of the modules.I use a DMTD setup to make the measurements.More additions to the original post will follow.Cheers,Corby

author: Theboel
author_rank: Frequent Contributor
timestamp: June 24, 2019, 01:05:20 am
content: very complicated equipment,I have user manual for this PHM may be can help

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: June 27, 2019, 05:11:07 am
content: Well I'm slowly making progress! Did some alignment and it's looking better now. AD plot is running overnight. The integrator mod, which appears to be factory, is why the op amp drift adjust does not work. Since the Maser will operate this way I'll wait to take care of this after I'm happy with the AD performance! Next step is to adjust the HFO frequency to a few different spots to see if the AD improves. I'll probably try 95, 100, 105, and 110 MHz .Cheers,Corby

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: July 02, 2019, 11:25:00 pm
content: Here are AD plots before and after the modification was removed and the alignment was also tweaked.I've also plotted the HP 5071A hi perf spec. and the old version (which mine appears to be) ch1-76 specs for comparison.Looks to be meet or beat specs at 4 Seconds and longer!Still chasing down some other optimizations to see if I can get it a bit better!Added some more info on the AD plots!Cheers,Corby

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: July 22, 2019, 01:02:36 am
content: Well the HFO frequency and nickel purifier temperature adjustments did not make any difference in performance. I also checked with both High and normal C-field currents with no change. I did install a new integrator module made from two late series HP 5065A A9 modules and the AFC meter indications now act properly. It looks like the very early module had no buffer on the op amp output. My unit appears to be a transitional unit with an odd 1 transistor buffer. The late model units have a more conventional 2 transistor buffer. PIX shows new module with stacked A9 cards on left and original Maser module on right. Still performing at or close to specs so I'm happy!Cheers,Corby