[SOLVED] HP 8563A Spectrum Analyzer Repair - Is the YIG oscillator dead? - Page 1
Forum section: electronics / repair

author: 1Ghz
author_rank: Unknown
timestamp: June 13, 2020, 11:13:38 am
content: EDIT: June 29, 2020TL;DRThe problem was caused by bad YIG oscillator.Replaced the YTO (YIG oscillator) and that fixed the problem.I recently bought an used HP 8563A spectrum analyzer.But it's not working and it displays an error messages.Code:301 YTO UNLK317 FREQ ACC334 LO AMPLHere is the pictures.1. 8563A1st LO Output (picture from the 8563E)It's not working correctly. No signal output from low to mid frequency range.2. 8563ACAL Output (picture from the 8563E)It's working correctly.3. 8563A Power Supply LEDsI think it's working correctly.Is the YIG oscillator dead? Should I replace the YIG oscillator?Thanks,

author: 4thDoctorWhoFan
author_rank: Regular Contributor
timestamp: June 13, 2020, 06:19:56 pm
content: Since you are displaying the cal signal correctly, it's not the YIG. Usually with a YIG problem, you will not get any signals to display.I'm no expert though.

author: MadTux
author_rank: Frequent Contributor
timestamp: June 13, 2020, 08:42:26 pm
content: Better look at block diagram of 8563A for YIG frequency sweep range before declaring YIG for dead.YIG of 8561E runs between 3-6.81GHz, somewhat close to those 5-7GHz you measured, probably also depends on what band your SA is set to.Low band 0-2.9GHz mixes it to 3.91GHz, so YIG should sweep beween 3.91-6.81GHz.High band 2.9 GHz and above downconverts it to 310MHz, so it should sweep 3.21-6.11GHzHarmonic mixing in bands above, probably similar to HP 8566Bhttp://www.simonsdialogs.com/2018/11/hp-8561e-spectrum-analyzer-30-hz-to-6-5-ghz-some-consequences-of-a-past-disaster/http://www.simonsdialogs.com/wp-content/uploads/2018/11/8561e-block-diagram-with-annotations.jpgPerhaps try setting the 8563A into zero span mode, then you can measure frequencies without sweep.YIG coil can also be tuned by current from power supply for basic testing outside of instrument, if you get crazy otherwise ;-DYour YIG is probably fine, btw, more likely the PLL is messed up, perhaps dried up capacitors or so, usually the first that goes bad if noone has messed anything up.

author: 1Ghz
author_rank: Unknown
timestamp: June 14, 2020, 10:02:42 am
content: Normally, YIG of 8563A runs between 3 to 6.81 GHz, too.More pictures.1. 8563A low band 0 Hz to 2.9 GHz sweep test1) Setup2) ResultNo low to mid frequency sweep.2. 8563A high band 2.9 GHz to 6.2 GHz sweep test1) Setup2) ResultNo low to mid frequency sweep.3. 8563A CAL output 800 MHz span test1) Picture from the 8563ANo 0 Hz LO feedhtrough displayed.No CAL output signal displayed.2) Picture from the 8563E4. 8563A CAL output zero span test1) Picture from the 8563ANo CAL output signal displayed.2) Picture from the 8563E

author: MadTux
author_rank: Frequent Contributor
timestamp: June 14, 2020, 11:30:45 am
content: PLL goes crazy on that one, YIG likely is fine.Try measuring tuning current (as voltage) on YIG tuning coil without sweeping, it should be a constant current(voltage), on your instrument, it's likely oscillating like crazy.The spikes you see are probably when unlocked PLL matches frequency at a sweep spot. A few MHz above or below on 8563E sweep, 8563A YIG has drifted to a totally different frequency, so it generates the wrong impression of no YIG output, when in reality it's just running all over the spectrum.

author: 1Ghz
author_rank: Unknown
timestamp: June 29, 2020, 11:13:48 am
content: Replaced the YTO (YIG oscillator) and that fixed the problem.I bought the YTO from Test Cal Instruments.1. -5 dBm 20 GHz CW signal. And no errors. Yay!2. Local FM station3. 2.75 GHz to 20 GHz sweep test

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 30, 2020, 09:45:58 am
content: Did you open the YTO assembly to see if anything could be done to it or just for the sake of autopsy?

author: 1Ghz
author_rank: Unknown
timestamp: June 30, 2020, 01:49:08 pm
content: Bad YIG oscillator photos.Inner circuitCoilsMaybe FM coil is burnt?

author: shakalnokturn
author_rank: Super Contributor
timestamp: July 01, 2020, 12:39:29 pm
content: FM coil does look a bit suspicious.I'm not sure what's been going on here either, looks as if it has heated enough to change the gold plating's colour.

author: dietert1
author_rank: Super Contributor
timestamp: July 01, 2020, 01:17:09 pm
content: Two years ago i fixed a similar problem on our HP 8560A. As far as i remember the YIG oscillator uses a special 28V voltage that comes from a voltage doubler. Those voltage doublers were made with electrolytical caps and those don't last as well, since on power-on they get reverse voltage every now and then. Replaced one cap and the spectrum analyzer worked again.The instrument is servicable, yet the power supply is buried deep inside, so it takes patience to get the board out. The capacitor has 3 pins with the third pin connected to a built-in shield foil. Made something similar from a normal cap and copper foil i had.Regards, Dieter

author: 1Ghz
author_rank: Unknown
timestamp: July 01, 2020, 01:53:50 pm
content: Quote from: shakalnokturn on July 01, 2020, 12:39:29 pmYes, it's suspicious! Maybe too much current? Hmm...Quote from: dietert1 on July 01, 2020, 01:17:09 pmIf it fails again, I'll check the caps.

author: romal76
author_rank: Contributor
timestamp: January 02, 2022, 11:34:05 am
content: I'm having 8561E with bad YIG (p/n 5086-7906).Is it possible to replace bad YIG 5086-7906 with another one 5086-7903? Which steps? How to make tuning after replace if it possible?

author: 1Ghz
author_rank: Unknown
timestamp: January 28, 2022, 08:01:04 am
content: Quote from: romal76 on January 02, 2022, 11:34:05 amSorry, I have no idea. I replaced it with same YTO.

author: romal76
author_rank: Contributor
timestamp: January 28, 2022, 09:07:57 am
content: It's working good, I was check it. 5086-7906=5086-7903Next problem for me is SYTF, broken switch.

author: 1Ghz
author_rank: Unknown
timestamp: January 28, 2022, 09:41:16 am
content: Quote from: romal76 on January 28, 2022, 09:07:57 amNice to hear that. Thanks for share your experience.Quote from: romal76 on January 28, 2022, 09:07:57 amHope you can fix it soon.

author: larry540
author_rank: Newbie
timestamp: March 03, 2022, 04:28:20 am
content: I am new to this forum and recently purchased a 8561e which 28v supply is running at around 7v. It turns out if I unplug the SYTF(5086-7803) the supply goes back to 28v. The SYTF looks to be pulling well over 800ma on the Tune input. I don't belief this is normal. Does anybody have any comments? Is there any hope of repair?