HP 8595E SYTF P/N: 5086-7803 PIN switch problem - Page 1
Forum section: electronics / repair

author: analogRF
author_rank: Super Contributor
timestamp: February 03, 2019, 08:52:53 pm
content: I've got a 8595E which works perfectly fine in the high band but it's about 24-26dB down (almost flat) in the low band.Long story short, by doing various measurements, I have confirmed that the PIN diode switch inside the SYTF whenswitches to the low band is dead (exactly 24-26dB loss over the band) so it does not pass the signal through to the mixerEverything after the SYTF works fine when I directly inject low band signal. The YIG filter itself is of course fine, too.It seems to me that the PIN diode in the shunt arm of the switch is shorted perhaps due to excessive input power.It also overloads the switch voltage that comes from A7 board, instead of -9.8V it becomes -3.6V when that switch is supposed to close. But for the other pole of the switch (high band) it is -9.8V as it should be. If I disconnect the wire, the voltage is back to -9.87V which is correct.Anyways, since I have never opened a SYTF or any YIG tuned stuff beforeI have a couple of questions I was hoping someone on this forum can help me with:1-what are my chances of repairing the switch and not messing up the YTF?2-Are the switch and the YTF in two separate compartments? If I attempt to open it upis there anything that might fall off and mess the whole thing up?3-is the switch made of wire bonded microcircuit elements? I don't have access to any wire bonding stuff. Only my soldering iron!I have also posted this on keysight forums and HP/Agilent Group.iothanks

author: analogRF
author_rank: Super Contributor
timestamp: February 03, 2019, 08:56:33 pm
content: ...Another solution that I am considering is to buy a microwave SPDT switchand put it between the attenuator and the input of YTF. For the high band the switch will pass the signal to the SYTF andit does its job perfectly but for the low band the switch will divert the signal directly to the dual mixer bypassing the SYTFThe biggest issues are (1) generating compatible switching and power supply voltages from what is already on the A7 boardfor that I will have to put is a small circuit somewhere! and (2) where to mount the switch in the RF compartment.There are some small spaces here and there and maybe I can squeeze it somewhere...not sureHowever, the type of the switch is critical. First I was looking at relay switches for example from Teledyne which havegood specs and relatively cheap but then it struck me that the switching times must be very small compared to the sweep speeds of the SARelay switches are rated at 5ms-15ms switching times. That might work OK for most of the time but if it happens that your frequency spancovers the transition between low band and high band and the sweep time is in the range of 10's of ms then it becomes a mess...that's whythe HP designers only used PIN switches in all places in the RF section. Modern analyzers use GaAs FET switches. The switching times for PIN diode switches are around 5-20nsec but of course they can never achieve the insertion loss and isolation specs of relay switches. not even close..Now the only thing I have been able to find was Mini-Circuits ZYSW-2-50DR and ZYSWA-2-50DR with reasonable specs up to 3GHz and even applicable up to 5GHz but not to 6.5GHz as I need.Any suggestion about a PIN diode RF switch that I can buy at reasonable price is welcome

author: kirill_ka
author_rank: Frequent Contributor
timestamp: February 04, 2019, 01:05:12 pm
content: I have HP 8561E using the same SYTF. In my case I had low output in the high band. Initially I thought that the switch is not working, but most likely YTF got detuned.Anyway, I've destroyed the switch during my experimentsQuote from: analogRF on February 03, 2019, 08:52:53 pmBesides the switch itself there are two devices that look like protection diodes.I'd try to find burn marks visually. If the diode is the only part which failed, may try to disconnect it by removing bond wire.Quote from: analogRF on February 03, 2019, 08:52:53 pmI don't think peeling the mesh from the switch side would significantly affect the performance. But also I have no idea how to glue it back in place.Quote from: analogRF on February 03, 2019, 08:52:53 pmYes, unfortunately. The switch is not a pin diode. Look for HMMC-2006 datasheet (I don't remember if it's the exact part of very similar). It's a GaAs SPDT switch.The interesting thing is that the switch is connected back to front - switch output is connected to the SYTF input. High band signal is not going through the switch, it's reflected back to the YTF part.Edit:"It also overloads the switch voltage that comes from A7 board, instead of -9.8V it becomes -3.6V when that switch is supposed to close. But for the other pole of the switch (high band) it is -9.8V as it should be."This probably means that the switch itself is dead.

author: kirill_ka
author_rank: Frequent Contributor
timestamp: February 04, 2019, 01:28:41 pm
content: Yesterday I tried too tune the filter. The result was predictable, the sphere snapped off from the rod. I should have used some fixture to control the movements.But that's only the 3d stage. There are two stages remaining, I must find a convoluted way to destroy them tooI've already installed a replacement SYTF, so turning attempt is just of curiosity.

author: analogRF
author_rank: Super Contributor
timestamp: February 04, 2019, 02:06:51 pm
content: Quote from: kirill_ka on February 04, 2019, 01:28:41 pmthanks for the info. So it seems, as I feared, the chances of fixing the switch is pretty close to zero.But I thought it was PIN switch because I remember somewhere in the service manual is says so...oh, well, GaAs FET or PIN does not matter now...I think I will have to go down the path of installing a new extra switch if that's possible but I don't know which switch is a good choice

author: kirill_ka
author_rank: Frequent Contributor
timestamp: February 04, 2019, 02:28:19 pm
content: Quote from: analogRF on February 04, 2019, 02:06:51 pmYes, that's the problem. You can't install a solid state switch in the same configuration as it is in the SYTF.If you use a relay, you'll probably need an external band switch.It might be possible to use the other half of the switch if it's alive. But again, it would require wire bonding or soldering a microscopic wire...

author: MarkL
author_rank: Unknown
timestamp: February 04, 2019, 08:44:44 pm
content: If it helps, here is the inside of a 5086-7803 SYTF from an 8595E.The high band was dead on this one so I decided to open it up. You can see the YIG sphere in the lower right which had fallen off its post and was lodged between the two coupling loops. The YIG sphere later rolled away and could not be found. Bye, bye, high band.EDIT: Added close-up.

author: analogRF
author_rank: Super Contributor
timestamp: February 04, 2019, 08:55:15 pm
content: Quote from: MarkL on February 04, 2019, 08:44:44 pmgreat pictures! So the switch is actually right next to the YTF side by side. Well, thats not what I can repair...at least the filter part works perfectly fine

author: madao
author_rank: Frequent Contributor
timestamp: April 27, 2019, 04:52:54 pm
content: I has a 8595E with fault in band 1. massive loss.I could repair him with soft power on YIG sphere-holder (plastic bloc) and its work again.But i dont guess, it is again in specification, but self-cal: passed.best regardsMatt

author: hackwell
author_rank: Contributor
timestamp: May 05, 2019, 12:42:01 pm
content: Higot a 8595E off Ebay recently , showing two issues.first the keyboard was not responsive at all, the sweep refreshes every minute of so. after some measurement on the YIG , it appeared to be dead.Installed a replacement from a 8594E and after a factory cal reload the operation was back to normal.the second issue is the same as described above. Spot on below 2.9GHZ but no signal in the high band. After taking the YTF filter appart guess what?yeah... misaligned spheres again.I managed to realign two of them but infortunately the one on the high band side had snapped off it's rod and my attempt to glue it back into position was a complete failureMy guess is that when the sphere is detuned to the point it touches the loop it snaps off shortly afterI thing the analyzer was used in low band until the YTO failed then was decommissionned.the rods are made of glass apparently so be very careful when touching them.I wonder what kind of glue they used in the first place ?Some interesting info on wire bonding on this page :https://www.qsl.net/ct1dmk/wbond_ex.htmlsome shops offer YIG rebuilding as well but the prices are... hum...EDIT : surprisingly enough the 8595E passed all self calibrations and confidence test with a dead YTF. Weird

author: Bicurico
author_rank: Super Contributor
timestamp: May 05, 2019, 02:39:20 pm
content: Questions (for my own satisfaction):1) Is the YIG sphere the small metallic sphere on the tip of what looks like plastic pens?2) Are there 3 of them? Why?3) You guys try to glue the YIG sphere back to the tip?4) Isn't the YIG highly toxic/radioactive/whatever = meaning: never touch it?5) If you lost one YIG sphere, what is the resulting danger, if it is lurking unprotected under your table? What if your cat/dog eats it?6) How exactly does the YIG work? I read about it, but it sounded like black magic...Regards,Vitor

author: hackwell
author_rank: Contributor
timestamp: May 08, 2019, 06:47:17 pm
content: Quote from: Bicurico on May 05, 2019, 02:39:20 pmYes indeed. the rods seem to be glass BTWQuoteThe three cells are used as filters to separate low band up to 2.9GHZ and the high band from 2.9GHZ to 6.5GHZ. The benefit of using YIG filters is the response speed allowing a continuous sweep across all the bandwidth without drop. Much precise and faster than switches.This is achieved by applying a magnetic field focused on the spheres. this adjust the frequency response accordingly.QuoteI did try that to no avail. used bi component epoxy glue but curiously enough it would'nt harden even after a whole night. and as the sphere is approx 0.5 mm diameter it's quite hard to put the right amount of glue at the good place and get the sphere in exact position.Anyway it is useless to glue it back in place as it is factory tuned by rotating the supporting rod and the chances are slim to get into specs after such a repair. I dunno if someone managed that already ?QuoteNope they are maily gems. Costs a fortune but not toxic at allQuoteThe main danger is to have to find another working YTF on the bay for less than $800QuoteAs I explained before it is a tunable filter. The center frequency is adjusted by a magnetic field. The ytrium is magnetic sensitive and acts as a tunable XTAL. In the YTF case the speres are used as filters the separate the two bands. But in a YIG oscillator it is used as a high frequency tunable oscillator

author: MarkL
author_rank: Unknown
timestamp: May 08, 2019, 10:51:48 pm
content: Here's a decent intro to YIG tuned filters:https://www.microlambdawireless.com/resources/ytfdefinitions2.pdf

author: Bicurico
author_rank: Super Contributor
timestamp: May 09, 2019, 09:09:52 am
content: hackwell and MarkL: Thanks!The article is great and reinforces my opinion that the YIG is some magical material! How on earth did physics came up with such properties?Regards,Vitor

author: madao
author_rank: Frequent Contributor
timestamp: May 13, 2019, 06:10:03 am
content: Quote from: hackwell on May 05, 2019, 12:42:01 pmUuuh, it means, my sucess with SYTF is not sure. I has only one SHF-Signalgenerator, it is from 1960s. Very heavy Rohde Schwarz gears carry up to four etage..no mood !

author: hackwell
author_rank: Contributor
timestamp: May 21, 2019, 07:48:36 pm
content: I don't know how the Rhode & Schwartz self calibrate. Used one for years when I worked in a HAM radio repair shop but we had a calibration service to care about that. Don't touch it little boySure enough all the 85xx HP series self calibrate with the 300 MHz calibration signal. So what happens when the high band fails ?EDIT : the YTF calibration passes as well. even with -16 dB loss.

author: hackwell
author_rank: Contributor
timestamp: May 25, 2019, 01:10:02 pm
content: I did some more testing on my 8595E . injected a 4GHz -16 dB signal into the hi band stage after the SYTF and the result seems coherent.So I opened the SYTF in search of spheres misalignment and I found the input one slightly off.I managed to put if back into place quite easily , as the rods weren't gluedweird !But this changed absolutely nothing.I'm now quite sure the problem is in the FET switch that turns on and off the low band. It appears to let the low band signal pass through when selected but I think the FET that grounds the the input loop when high band is selected doesn' work anymore.It's becoming tricky ! I don't know if I even could probe that without destroying the switchIf anybody has and idea about what I could try ?

author: kirill_ka
author_rank: Frequent Contributor
timestamp: July 08, 2019, 01:01:40 pm
content: http://www.simonsdialogs.com/2018/12/hp-5086-7803-yig-tuned-filter-and-switch-sytf-details-and-adjustment/

author: kirill_ka
author_rank: Frequent Contributor
timestamp: July 08, 2019, 01:07:40 pm
content: Quote from: hackwell on May 25, 2019, 01:10:02 pmNot likely. The switch doesn't affect the HI band path significantly.

author: charlyd
author_rank: Frequent Contributor
timestamp: January 21, 2020, 10:28:01 pm
content: hello with a message on a 8595E amplitude out of spec > 3ghzis that someting to do with the YIG.

author: analogRF
author_rank: Super Contributor
timestamp: January 22, 2020, 01:43:13 am
content: Quote from: charlyd on January 21, 2020, 10:28:01 pmIn all likelihood, yes, it's the SYTF fault. There is a small chance that the driver of the SYTF is faulty too butin all cases I have seen (8595E, 8596E, or 8563E which is more complex because it also has a mixer in it) it is always the YIG filteror the switch that is integrated in the device.a bit more info could be helpful though, if the "out of spec" means it's almost dead for the high band like >10-15dB offthen refer to what I explained above but if it is like 2-3dB off then it could be the calibration which is pretty easy to do.

author: charlyd
author_rank: Frequent Contributor
timestamp: January 22, 2020, 06:37:22 pm
content: @analogRF may i come back to you when i know more..it is still coming

author: analogRF
author_rank: Super Contributor
timestamp: January 22, 2020, 08:25:07 pm
content: Quote from: charlyd on January 22, 2020, 06:37:22 pmabsolutely, i hope i can help. you can pm me.

author: charlyd
author_rank: Frequent Contributor
timestamp: January 22, 2020, 09:34:13 pm
content: can i test this with a cal ( cal cable loop) i am new to SA , sorry.

author: analogRF
author_rank: Super Contributor
timestamp: January 22, 2020, 09:55:00 pm
content: Quote from: charlyd on January 22, 2020, 09:34:13 pmif the problem is the high band (>2.9GHz) no, not really. Only the last 5-6 harmonics of the cal are visible at the beginning of the high bandand they are falling off quickly so it will not give you an indication of what (if any) is wrong with the high band

author: OH2LIY
author_rank: Contributor
timestamp: January 23, 2020, 07:37:38 pm
content: Hi, HP8595E is quite easy to convert HP8593E. Remove broken SYTF and grab YF85 or similar YTF (I got mine from eevilbay under 100€). New YTF needs 24V from power (there is wire all ready for this). Then there is need to add RF relay to switch lo/hi input to mixer. Original attenuator 10-30dB steps are usable over 20GHz. Biggest PITA is to make calibration after identity changeRamppa