Trouble with a 3.0 - 6.8Ghz YIG Oscillator - Page 1
Forum section: electronics / testgear

author: jlmoon
author_rank: Unknown
timestamp: March 10, 2015, 07:22:02 pm
content: I have been evaluating a case of trouble with a Hp 8563a and beginning to scratch my head a little.Could someone give me some clues to why my YIG output would be varying in amplitude when performing some basic span / LO functional test per the Hp service documents. What I am encountering is this: I can dial up some frequencies setting span to zero and when I dial to some areas the YIG LO goes to no output. I have a video that actually shows the LO behaving correctly until it reaches an area of the programmed span and then poof the LO amplitude drops into the noise. Turn the analyzer center frequency back down a little and the LO fires back up and all is good, approach the edge of trouble and the LO output drops 30 - 40db in level until it disappears. Currently I am not seeing any signal from 0 to ~2.7 Ghz , 2.8 to approx 3.1 Ghz all is good, go above ~3.2Ghz to the top end of 26Ghz and the output drops off again. Isn't it correct to assume the YIG output should not vary in amplitude but only frequency based on the current imposed on the Loop coil. After all this is the LO input to the mixer which derives your frequency of interest.Any advice would be greatly appreciated.Thank you,JLM

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: March 11, 2015, 05:43:26 pm
content: Are you getting any error messages?Here's a link to the (similar) Svc. Man. if you don't have it. might be useful.I have an 8560E, but no trouble yet. I also repaired my Gigatronics freq. synth that had YIG CAL errors on start up. Replaced the YIG. Same prob. Was the Divide by N module.http://www.ko4bb.com/manuals/198.231.9.145/HP_8563E_EC_Service_Manual.pdf

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: March 11, 2015, 07:26:56 pm
content: Not sure this applies to the A version, but most likely...

author: AF6LJ
author_rank: Unknown
timestamp: March 11, 2015, 09:17:49 pm
content: I don't know if you know this but YIGs age, they develop variations in output and will stop all together at parts of their former frequency span.If you have a minimul microwave test bench you can test the YIG.

author: jlmoon
author_rank: Unknown
timestamp: March 12, 2015, 02:22:10 pm
content: Quote from: AF6LJ on March 11, 2015, 09:17:49 pmYes, I have heard that is the case. Yes I pretty much have everything to test upto 26Ghz. Only problem is finding documentation for my 5086-7781 YIG. I am beginning to lean towards a PLL problem due to the fact that the YIG has output on some frequencies but not others. A 8563A is a bear to obtain accurate schematics so as to do so real test and verify module function.If I can't find the trouble, I may wind up throwing it up on the top shelf for another days challenge.Taking it a day at a time here with this one. Thank you for all the advice.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: March 12, 2015, 02:58:34 pm
content: For the lowest frequencies, the Fractional N (in the PLL) is determining how to control the YTO. Disabling the PLL and controlling the YTO manually is a good way to see if the instructions it gets are correct, or not.Good luck in your troubleshooting. Again, here is some info on the E version, probably similar to the A.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: March 12, 2015, 03:40:27 pm
content: found the 8560A SVC man on the KO4BB site. Probably closer to your 8563A...http://www.ko4bb.com/manuals/198.231.9.145/HP_8560A_Service_Manual.pdf

author: jlmoon
author_rank: Unknown
timestamp: March 12, 2015, 03:43:22 pm
content: SoundTech,Thank you for the screenshots. With the 8563A there are some minor differences to the procedures but only minor.I am in the process of going through sections 11 & 12 in the 8562A/B Service Manual Vol1.Testing the 1st LO output, I am getting proper output only in some areas. I have attached some notes I took on my first time around with this, I will be starting all over once again to move closer to a dividing point so I can lay to rest a YIG failure. The errors I am getting point to a YTO Loop which are 301 YTO UNLK, 317 Freq Acc (Which points to the Main Coil Coarse DAC on the rails) and 334 LO Ampl (Which I presume would be when the LO is in no output mode or unlevelled)This machine only has 700 hours from new date, but still is around 20 years old so who knows could still be a bad YTO.. just hope not!

author: jlmoon
author_rank: Unknown
timestamp: March 12, 2015, 03:46:08 pm
content: Quote from: SoundTech-LG on March 12, 2015, 03:40:27 pmRegarding page 2-38 I was able to perform that test and adjustment, infact it was almost spot on.

author: AF6LJ
author_rank: Unknown
timestamp: March 13, 2015, 01:58:51 pm
content: All I can say at this point is good luck. YIGs are like Hens Teeth, fragile and hard to find.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: March 13, 2015, 02:15:25 pm
content: I put an email notification search in ebay, got the Gigatronics YIG for $25.00 but since that part was working just fine, I now have a spare just in case. So there is some luck involved.

author: albert22
author_rank: Regular Contributor
timestamp: March 13, 2015, 03:59:21 pm
content: It seems that this guy can repair YIGshttp://www.qsl.net/ct1dmk/wbond_ex.htmlMay be he can offer a solution.