Author Topic: First Spectrum Analyzr HP 8590A (Read 3579 times)

Crambone · « **on:** August 20, 2019, 02:42:31 am »

Hello, I recently picked up an HP 8590A that showed it passed all the CAL tests. I’m not sure if I’m doing something wrong but when I inject a 27.50MHz frequency into the 50ohm input I’m not seeing anything. I’ve tried slowly amplifying the signal but don’t see the one I’m injecting. I do on the other hand find one that’s 2-3MHz off frequency.
To get we’re i am I insert the signal (27.5) go to Starting freq 26.0MHz and Ending at 28MHz. I then see a 3 spikes one small one lager and one small but all are not the frequency I’m injecting.
Am not seeing something?
Beginners mistakes?

Thank you, Drew

MarkL · « **Reply #1 on:** August 20, 2019, 02:40:42 pm »

Did you run the calibration yourself or do you mean you only saw a picture of it completing calibration?

What are you using as your test signal source?

How about some screenshots of what you're seeing?

chrisl · « **Reply #2 on:** August 20, 2019, 03:52:15 pm »

Do you see the correct level and freq of the cal signal if you connect the input to the cal output using a short cable?
Please upload some pictures of your setup including the signal source and screen shots of the S/A so we can see the setting of the S/A and the generator.

Crambone · « **Reply #3 on:** August 21, 2019, 12:50:52 am »

Well maybe I should start at the beginning, when turned on the screen jitters. https://youtu.be/rmj_mluO1BY
After warmed up it looks like pic.

Crambone · « **Reply #4 on:** August 21, 2019, 12:56:08 am »

Im going to let it warm up for 2 hours and then run the Cal Freq, Cal Amptd, Cal Store then I will retrieve the screen requested and add a photo of its findings and corrections.

Crambone · « **Reply #5 on:** August 21, 2019, 04:01:15 am »

Pic after cal and conf test. Well now it seems to be almost in the ballpark?

? I don’t get it maybe it didn’t warm up enough first time I ran the cal. It’s showing it only off .14 to .24 MHz now.
First pic is frequency gen
Second oscilloscope
Third HP 8590A

chrisl · « **Reply #6 on:** August 21, 2019, 07:20:28 am »

It does not look bad... I would zoom in more by reducing the SPAN to only 2 or 3 MHz or even narrower.
Also you may want to try using the same 10Mhz ref for both the sig gen and S/A.

Crambone · « **Reply #7 on:** August 21, 2019, 01:32:51 pm »

Yes after playing around with it last night I did place both at 10MHz reference and zoomed in and it was almost dead on.
Thank you for your help.
Did you get a chance to look at the video of the jittering when first started? Also my intensity knob needs to be almost fully clockwise so I can see the screen.

SilverSolder · « **Reply #8 on:** August 21, 2019, 04:40:56 pm »

The start-up jitter looks like a vertical deflection circuit issue - probably components have drifted so the frequency has drifted too, so it struggles to sync with the video signal until it has warmed up a little. This issue can probably be fixed with a slight screwdriver tweak of some pot somewhere, to bring the vertical oscillator back in easy capture range.

Smoky · « **Reply #9 on:** August 22, 2019, 08:59:41 pm »

In the menu, you'll find a selection named "Cal Data."

It will bring you to a screen filled with several columns of numbers.

Take a picture of it, and post it here.

Crambone · « **Reply #10 on:** August 22, 2019, 09:30:26 pm »

CAL DATA

Smoky · « **Reply #11 on:** August 22, 2019, 11:11:21 pm »

I researched these HP 859X series of Spectrum Analyzers about two years ago or so, then I stopped.

The #1 problem is the "age" of their internal parts.

The mixer diodes in the first converter will degrade and eventually short or go open, and as time goes on, the DAC range and the accuracy in regards to "amplitude" slowly drifts.

The diodes were made and matched by HP. No individual or packaged diodes that I've seen used as replacements are able to bring the DAC range back into spec.

In the picture you took, the RL-VENR column is the tell-tale. The uppermost number should be between 230-245 and the lowest number should be between 3-20. This scale is in the service manual. Btw, on other machines, I've seen RL-VENR numbers start at the top being as low as 185.

The ERR and SGAIN numbers should reflect a very small fraction, somewhere between 0.00 and .25.

If that isn't enough, the attenuator also degrades. They were once made by Wavetek, so if your attenuator tests bad, you'll need to find another machine to scrounge one from. I've seen a few attenuators on Ebay for ~$100, but remember, they are also used.

I've researched the 856X series as well and it suffers too but to a lesser extent. I believe the 856x's are "lab-grade" analyzers anyway.

I am a beginner in electronics, so the way that I'm describing this may not be 100% accurate.

Crambone · « **Reply #12 on:** August 23, 2019, 12:31:53 am »

I was told to replace the existing diodes bad or not with 1N5712 as it has just about the same junction capacity (2 pF vs 1.2 pF). I was also told to replace all the electrolytic capacitors as we know they fail after time and will drift from spec.
I believe I’m going to open it up and check the 1st Mixer Element for loss? I will also replace the diodes after and check again. I’m hoping the attenuator isn't degraded it’s my first go around with an analyzer as I’m new to this also. Some of the issues I first experienced were purely my inexperience on how to properly use the analyzer.

Smoky · « **Reply #13 on:** August 23, 2019, 01:29:53 am »

I recall these Schottky diodes were used as a replacement for the original mixing diodes in one project, and they came darn close to factory spec.

After it was all said and done, the bottom number in the RL-VENR column was ~35 in the HP 8590A spectrum analyzer that was repaired.

I think his final choice of diodes was part number HSMS-2812.

Here is a snapshot of the spec sheets:

Good Luck

Crambone · « **Reply #14 on:** August 23, 2019, 02:29:31 pm »

Thanks for all the help and giving of knowledge I appreciate it!
Great site with tons of knowledge!

Crambone · « **Reply #15 on:** August 27, 2019, 12:51:08 am »

Well I replaced the mixer diodes in the first converter today they did test good but figured while I had it out I would just pop in the new ones. Got it back together ran the cal and it was very close to being on frequency. I was feeding 27.5 MHz AM 30% at .5watts. My peak on the analyzer was 27.67. Let it track marker for about an hour and it drifted down to 26.5 MHz with Span set at 3 MHz.
Wondering were to look next? What can be causing that drift?

Crambone · « **Reply #16 on:** August 27, 2019, 01:21:41 am »

Correct after diode replacement

MarkL · « **Reply #17 on:** August 27, 2019, 04:21:39 pm »

The drift spec for the 8590A is <50kHz over 5 minutes after a two-hour warmup (from the service manual in the performance verification section). Did you meet the warmup and time requirements? The full list of frequency and other specs are split between the service manual and the installation/verification manual.

There's going to be some drift and you're not going to get super-accurate results, like you would from a frequency counter. Later models in the 859x family have a counterlock feature to combat drift and provide more accurate frequency results.

Crambone · « **Reply #18 on:** August 27, 2019, 06:55:20 pm »

Yes I allowed a full 2 hr warmup and test was performed directly after calibration. I noticed the drift after a few minutes so I’m thinking it’s in spec


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Author Topic: First Spectrum Analyzr HP 8590A (Read 3579 times)

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