#1 [Repair/RF] HP 8591A Spectrum analyzer

[@TonyBarr99]

Thank you for this excellent video. I have a broken HP 8591A instrument like yours that I rescued from getting scrapped at a former employer. Now that I've watched your video, I am now inspired to dust it off and attempt the repair. In my case, the LO is OK, there is just a failure that occurs during the amplitude calibration procedure. Thanks again!

[@bansci]

Thanks! Let me know how you get on and I'll help how I can. I was thinking of trying to get the spares unit working but I don't have a screen or YIG, so I can also get you parts if needed.

[@Berk-lf6ge]

Really cool video. RF is a such a fascinatig field to study and you really know a lot! Please dont stop doing videos like this, they are super fun to watch and study

[@sm6fie]

This was a really nice and instructive video. Thanks for sharing.

[@bansci]

You're very welcome!

[@herbertsusmann986]

Thanks for great video on this SA. I have an 8591E with tracking gen and it has been great. I always leave a 20 dB attenuator attached to the input by default and only remove it when necessary. One technical tip on your video. Your audio level between clips was all over the shop some clips were so low I could barely hear you even with volume very high.

[@bansci]

Thanks, glad you liked the video. In the end, I don't think I killed the unit as the YIG that died is hidden behind many other devices which would die first. About the audio, I've got a mic I can attach now to help level the audio out, but I need to figure out volume leveling filters too. Thanks for the feedback!

[@herbertsusmann986]

@@bansci On the audio. You can do a lot of level adjustments in the video editing software usually also.

[@bansci]

Yeah, that's what I mean by the filters. Didn't find it last time but will take another look!

[@solodolo6018]

Thank you very much for this video. Very informative. Theres an 8566b near me im thinking of picking up. It needs a new battery but i dont think thatll be a hard replacement. Luckily its a model that doesnt use the battery to store cal data from what ive read.

[@sparkfly7228]

Enjoyed your video - an interesting LO failure!

[@bansci]

Thanks! I really didn't expect it, but I saw a comment on eevblog forums after my repair that this is becoming a common age-related failure for these units now...

[@egbertgroot2737]

Beautiful that look inside the YIG !!!! Is the output of the YIG controlled with a PLL?

[@bansci]

I'm not sure if its a PLL, but there's a control loop. In the video at 41:50 you can see a shot of the underside where there is a golden part marked "5086-7806 RF Sampler" near the top. That is measuring the frequency of the YIG to close the control loop. Interestingly its on the opposite side of the instrument to the analogue board that controlls the YIG, so I think it might be a frequency counter and a digital control loop/self calibration is used to tune the YIG. You should note that the YIG is current controlled too, not voltage controlled.

[@ruhnet]

Yes it is in a PLL.

[@thetechgenie7374]

Likely coincidence that that YIG/LO failed and not overloading the input? It is a common failure point with those older HP’s I seen over the years. They don’t take shock well, newer spectrum analyzers actually uses a shock pad screwed to cavity to help a absorb shock. I had to fix one that had a bad counter/divider as signal was free run pretty much. When buying test equipment from depots especially military equipment they get toss about, or even left outside and etc? So likely wasn’t anything you did to make it failed, it just likely failed due to age? I don’t think you killed it? It likely passed due to natural causes? If was a overloaded input the attenuator or mixer the first converter assy would have failed instead? So you were correct to suspect that, as would have assumed the same. Great video on a nice piece of gear.

[@chaolinshi1816]

非常专业👍谢谢❤

[@xwarp]

Did you ever get a tracking generator for this unit? I have an 8591e and would like to get a TG for it.

[@bansci]

Yup, my next video is about hacking one to work with it kzbin.info/www/bejne/o2PJna2Hgq1-oJo. You can also read about it rather than watch the video here: groups.io/g/HP-Agilent-Keysight-equipment/topic/24815717?p=,,,20,0,0,0::Created,,8591A,20,2,0,24815717,ct=1&ct=1

[@erwe1054]

прикольный балун для смесителя на отрезке коаксиала

[@vidasvv]

OUCH, that must have hurt ! Just curious, why were you applying DC to it's input ? I love my 8591 with the TG and I've been putting off changing it's battery for years! Same with my 8593 and a fully loaded 8595. What ticks me off is the 8595 was at the cal house 2yrs ago and I just found out last week that they did not change it. Ya, without knowing those cal settings they make dandy paper weights! Glad I ran into your video, maybe now I will order new batteries for all. TNX 4 the upload! 73

[@bansci]

Absolutely, if you don't write them down you're toast. At least these older HP units have comprehensive manuals with forms to fill in helping you write them down!

[@germanjohn5626]

easy to do, use a simple 5V wall wart, add 2 diodes in series with a 470 ohm into the positive line and tack the now 3v paralel to the battery onto the board with the wall ward plugged in and the main power off and disconnected you can un-solder the battery and install a new one. Remove your external supply and you are fine to go.takes all but 5 min once the unit is out of the case. I have a supply made up just for that as I replace batteries for other quite frequently.

[@AECRADIO1]

THE Lo MIGHT BE A FULLY SOLDERED ENCLOSURE. PROBABLY SIMILAR TO A TCXO/VCO WITH SMA OUTPUT. YOU MIGHT ONLY GET ACCESS THROUGH THE ADJUSTMENT PORT, COVERED BY A SCREW.

[@bansci]

I got lucky in the end.

[@egbertgroot2737]

Did i understand you correctly that there must be coax between 10 mhz ref output and ext ref in?

[@bansci]

Yes that's right. If you don't put that in you get a warning, Ref unlocked I think. The system still works but you have reduced performance.

[@AECRADIO1]

THE CIRCULAR DEVICE, LOOKS LIKE A D.R.O. PROBABLY PART OF THE MIXER ASSEMBLY, AND DRIVES THE TRACK/GEN. OUTPUT.

[@bansci]

Do you mean inside the YIG?

[@AECRADIO1]

THE COIL RESONATES THE YIG SPHERE ACCORDING TO FREQUENCY.

[@bansci]

Yup! There's two coils, coarse and fine. The coarse coil current-to-frequency relationship is measured by calibration, whereas I believe the fine tuning coil is controlled using a digital control loop and the RF sampler (frequency counter) on the underside of the unit.

[@Samucas81]

Hello, I need firmware for my hp 8594A, could you help me? Thanks.

[@bansci]

Sorry, I don't have one of those units or the firmware...

[@Samucas81]

@@bansci Ok, no problem, tnks

[@AECRADIO1]

LUCKY YOU. A SCREWED DOWN ENCLOSURE. PHYSICAL ABUSE MIGHT HAVE DAMAGED THE YIG SPHERE INSIDE.

[@bansci]

Yeah, I didn't tilt to examine the sphere so its possible. I'm not sure what the common failure modes are for YIGs, I haven't got a SA with a high enough frequency response, otherwise I'd try running the YIG to see if it has any output. I also should try measuring the resistance of the coarse and fine tuning coils to see if they're OK.

[@Aligreta]

Video is good but audio is too bad

[@ruhnet]

I thought the audio was ok. Could be more normalized but it wasn’t hideous.

[@bansci]

I've finally figured out how to normalise audio in kdenlive AND what KZbin's loudness is, hopefully this is fixed from video #4 onwards. Unfortunately I can't upload edited videos on KZbin, so I'll have to leave this here with its somewhat crappy unlevelled audio.

[@uploadJ]

@@bansci Bravo! Continuous improvement is the goal!