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Old 20th Feb 2019, 8:58 pm   #1
Y2KEddie
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Default HP8569A Spectrum Analyzer , Operator Error /Troubleshooting

Troubleshooting my HP 8569A Spectrum Analyzer, Operator Error?
I recently picked up a HP 8569A spectrum analyzer. I tried searching the internet for documentation but cannot find a schematic for this particular model. The web sites indicate the model “A” but when I download, it comes up as a completely different model, or with a suffix “B”. The “B” model has a much higher frequency range, but seems to be somewhat similar, so I’m trying to get by with the “B” documentation. The manual is 600+ pages and a bit overwhelming to view online. I‘ve printed some sections and continue to persist.
The unit powers up and I do get a trace on the CRT; a random horizontal trace (looks like noise). If the front panel input filter is selected the noise “cleans up” as expected. All the front panel controls seem to have proper effect. As I progress through the pushbuttons for: frequency select, sweep change, span, attenuation etc , the display changes.
When I connect my shop scope to the rear panel BNC connector output:
Horizontal: displays a saw tooth (sweep output)
Vertical: displays noise (same as instrument display)
The on- screen digital display seems correct, as I sequence the controls: frequency, attenuation, etc.
I tried feeding the 100 Mhz Cal signal from the “BNC” jack to the “N type” input jack” on the spectrum analyzer, and see no change of signal on the display
I attached my other shop scope to the “BNC type jack”, 100Mhz cal output and see no signal. I rotate the attenuator on the analyze through its range and get nothing at the output jack. My shop scope is only 30 Mhz bandwidth but I believe it should show something.
I’ve tried feeding other external signals to the “N” connector and get nothing. I tried connecting my Cable TV to the input with no result.
I can’t seem to get any input signal to display. I’m guessing one of the input stages is defective. I thought if the 100MHz Cal signal was working I would be able to see it as a center marker on the display.
There are a lot of power supply voltage test points marked thru out the chassis , and all measure correct.
Maybe it’s operator error. I’m unsure how to operate or troubleshoot this particular instrument.
I’m taking a shot-gun approach to troubleshooting . Without a proper schematic and not knowing what the respective controls are supposed to do, I am at a real disadvantage.
Can anyone tell me how to set panel controls to display a familiar “ blip” waveform to verify this instrument is working?
I sure would welcome some guidance.
Thank you,
Eddie
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Old 20th Feb 2019, 11:15 pm   #2
kevinaston1
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Default Re: HP8569A Spectrum Analyzer , Operator Error /Troubleshooting

Keysight (HP) site says they offer the 8569A Owner/Service manual

https://www.keysight.com/en/pd-8569A...9&cc=GB&lc=eng


Kevin
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Old 20th Feb 2019, 11:46 pm   #3
Radio Wrangler
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Default Re: HP8569A Spectrum Analyzer , Operator Error /Troubleshooting

The calibrator output is either -20 or -30dBm, and allowing for the roll-off of a 30MHz scope, you may well not see anything, or simply not trigger even with a working calibrator.

I'm afraid the single biggest cause of failure in a spectrum analyser is someone connecting a transmitter without enough (or even any) external attenuation.

If you tune to 0MHz, certre, and 100MHz per division with the resolution bandwidth at 1MHz
and try different amplitude settings, can you now get a response on the screen?

This is the LO leaking into the IF as it sweeps across it. This should even work with a damaged input attenuator or mixer. The "zero Hz response" would prove your LO and IF onward were alive.

David
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Old 21st Feb 2019, 3:25 pm   #4
Y2KEddie
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Default Re: HP8569A Spectrum Analyzer , Operator Error /Troubleshooting

Thank you for your response.

I have found the problem. Antennuator shaft was frozen/locked up. Once freed up I was able to get a display using the calibrator output.
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Old 21st Feb 2019, 9:47 pm   #5
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Default Re: HP8569A Spectrum Analyzer , Operator Error /Troubleshooting

That qualifies as a very easy fix, compared to some of the ones I've come across. The zero hertz blip is a very useful diagnostic tool on spectrum analysers. I used to work in R&D for the analyser side of HP.

Be careful with the ref level knobs, they're all getting to the brittle age.

David
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