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- Опубліковано 25 чер 2024
- In this episode Shahriar troubleshoots a defective Agilent N9020A 8.4GHz spectrum analyzer. The instrument reports LO Unlock and refuses to perform any sweep at all. The complete block diagram of the instrument is presented with focus on the LO generation blocks.
The teardown of the instrument reveals the individual assemblies presented during the block diagram overview. After a few measurements, it is concluded that the LO Synthesizer module is faulty. The module is presented in detail and various components and signal paths are identified. Extensive measurements are carried out until the fault is traced to problems in the varactor bank of the main VCO. After the component replacement, the instrument is fully functional. The X-Ray of the synthesizer module is also presented during the repair.
The Signal Path
www.TheSignalPath.com
/ thesignalpath
www.Patreon.com/TheSignalPath - Наука та технологія
Overheard in the Keysight lab: "Let's embed 'Hi TSP' on a middle PCB layer that can only be seen on x-ray"
After watching this repair, I am glad someone knows how to read custom chips for what they DO, not what they ARE.
"Hey I see you're watching TSP."
"Yup, now be quiet I think I have a dead hex inverter in this C64"
"And what is Shahriar fixing?"
"ummm...."
Thank you so much for your teaching dedication. I will never use this really good information as I am old 75, but understanding what is going on is invaluable. When on an AIRForce base while out running 20 years ago, my son mentioned that is the radar shack. And I asked how many people work there? He said 200 to 300, and I was supposing 8 to 16 people, 200 to three hundred told me a lot. Radar returns are analyzed, reanalyzed, and then analyzed some more. The machines you have repaired on this site are the type of machines a lot of the information is based upon, and recently in the last 10 years our radar capability has taken a huge leap forward, so I am positive every one of your microwave boards is in use preparing the signal for these grunts to analyze and your mystery chips are that for a reason. NATIONAL SECURITY.
I love the wall of instruments as you pan around! Then you have a security system - cameras, bars on window, and of course, the cat!
The cameras lead prospective criminals into a false sense of security because Pooch is the real security system.
Question is though: are the above mentioned prospective criminals intelligent enough to understand what those instruments do and what they are worth?
....probably not. Not just that....the weight of a network analyser would put their backs out in seconds few, lol
Cameras, bars on window? The cat is more then enough.
@@dtiydr - Until a CAT burglar decides to target Shahriar... This way he's kept ALL bases covered
@Kevin A. , This is the MODERN WORLD, where anything is (unfortunately) possible.
@25:17 birdwatching!
Brilliant video thank you. So clearly described that I was anticipating your next move a few times. Normally I'm running to keep up.
Two videos in one day 😍😍😍
Thanks for the great videos, you have given me some ideas on some additional test and measurement equipment to purchase that I thought I would never have a use for. I normally don't buy T&E gear that's broken but I have before and discovered like in some of your videos, it's nothing more than loose cables or components. Keep up the great work.
Nice to see how several generations of the same spectrum analyzer work.
Thank you very much for your brilliant videos.
I recommend to show us how you tested the defect diodes (using a function generator and a scope?)
This kind of details would educate many of us even further.
Regards from Germany
Keeping them matched would be "challenging."
Woohoo two videos in a day!
And another great episode, love the x-ray analysis also!
Very-very impressive and nicely executed work.
Helpful repair video. I like it.👍
Another monster troubleshooting process...👍👍. It would be nice to see x-ray machine 🧐🧐.
Thanks for putting efforts in making this video.
Good job sir 👍 Thank you 🙏
Nice piece of kit and a good result
Amazing repair video as usual, but better, i like how you went completely down the rabbit hole and it didn't turn out to be something "simple"(well, on the other hand we can say that it can't get simpler than a dead discrete diode)
Nice x-rays and nice MXA work.
You are a genius bro ! good job ! keep up the excellent work.
The mind boggles ... thanks!
"Even if it doesn't go high in frequency " 8GHz is low frequency for him !!
And I'm sitting here with my 1.5Ghz NanoVNA and 100mhz Rigol scope :(
Actually for a microwave engineer everything below 1GHz is DC :)
Adam Turowski .... Damn !.... I could not get over 110MHz of FM business ever , nothing will be controllable or manufacturable with me ...
GHz is DC :-)
Another great video Shahriar. I don't remember you reviewing that RTO2064. Would be cool to see it put through paces. :)
Great video, thank you!
What x-ray machine? Very cool that you have access to that because it definitely brings an extra dimension of visibility into your analysis. Thanks as always.
Right?! I can use one of those!
Thanks for this video. I have a very similar failure of the 1st LO in a IFR/Aeroflex FM/AM 1600. I wish I had a schematic for it. But I will go in and check the Varactors and see if I can detect something there.
25:16 most important piece of equipment in any electronics lab
Notice the good lock on tail oscillator.
Wow, so much via stitching on that board! The PCB fab must go though a lot of drill bits manufacturing those boards :-)
They are highly needed but they cost more.
GOOD JOB
I would love to hear you talk about BAW filters
My usual method for diagnosing a PLL/VCO loop is to break into the loop and supply either my own VCO control voltage, or my own feedback frequency, that way you can work out what is causing the loop to break down.
This would not work here. This is a dual loop PLL. The digital loop cannot be broken.
Another awesome Video Sir. Your way of Explaining things is the best on You Tube in your area of expertise. Well Done Again Sir. My Patreon donations are well worth it
Looks like Vitramon capacitors on that custom probe tip.
شكرا على الفيديو هذا إبداع منك . كم من الوقت حضرت لهذا الفيديو . شكرا
Could you do a video on EMC? 😁
Regarding doing PLL in FPGA vs dedicated chips -- I was under impression that FPGAs had an order or two of magnitude more jitter (another way to look at the phase noise) than components designed specifically for RF frequency generation? But maybe it does not really matter, is the loop bandwidth is quite low?
... meanwhile I'm still working out cathode biasing and the HF grid stopper on my 12AX7.
I'm no Art Fong. (RIP)
Hey Shahriar -- could you possibly post those x-ray pictures somewhere? I'd love to take a closer look at them!
Shahriar: you mentioned you changed an OPAMP on the output of a DAC on the other side of the board. Was that a red herring? What made you suspect it?
It was a buffer right after the DAC which sets a course tuning of the VCO. If it has any issues, it would explain the problem.
A little light on why you replaced the varactor diodes, however I really do need to re-watch some videos, got lost around the FM part of the feedback loop.
still, interesting as always and a nice deeper dive.
I'd actually love to see some varactor diode experiments on this channel
Simple explanation: all PLL components gains have to be just right to get stable PLL loop.
More advanced explanation: kVCO of this PLL was marginal causing lack of enough phase margin and loop instability at certain VCO frequencies. kVCO is directly determined by varactor characteristic. In this design 8 identical varactors were used. Shahriar measured them and found that 2 were different than the remaining 6. Replacing 2 odd ones brought kVCO back to where it supposed to be and fixed the problem.
@@adamturowski3765 He found two were different /after/ replacing them though and combined with it working this confirmed his None of the measurements up to that point showed anything wrong with it. I got the impression it was more a 'I really don't want it to be deeper in so I'll try this [no reason given why this and not somewhere else in the loop] and see if it fixes it' decision, rather than as a result of any direct measurements.
@@ElectraFlarefire I spent another 4 hours making other measurements. Carefully looking at every waveform, looking at where things may start to look suspicious or abnormal. Just because it was not recorded, it does not mean it was not done. Furthermore,
Adam Turowski right above explained it to you already.
@@Thesignalpath Thanks for the response. I have no doubt that you know what your doing, it was more a comment that it felt like there was a missing part of the diagnostics in the video and from my point of view 'why try and replace this component' was never really explained.
👍👍
great job, but no cat scan
We need a new video!
Soon!
ebay to the rescue,at the end is a parts changing job,but which component is the culprit ?
Yes I would have replaced one at a time.
How does a seemingly random component on a huge system like this fail? I'd assume that if someone fed too high voltage, things would more visibly get destroyed or closer to the devices input get affected. Does anybody have a theory on how this could have happened?
I'm not an expert but these components are far from the input so it's impossible for a high input to reach them. It's normal for the first input components to fail under overload.
As to why this has happened it's guess work.My only observation is that I would have replaced one item at a time to see exactly which ones were at fault and that might have given a clue.
@@jonka1 Thanks for your reply. If it's not electrical misuse, then could it be aging related to temperature or other physical/environmental conditions that makes these components so far down the signal path fail?
But also kind of hard to believe since how seemingly well engineered these devices are. Maybe it is from how close to their limits or maximum ratings these components are being run that makes them fail?
Very puzzling, especially since this is not the first of his repairs of this high frequency stuff that has these "obscure" component failures.
@@user-mh6jy9ho9k All components are manufactured and bought in to build equipment. I repair and restore many pieces of old test equipment and semiconductors are just one of the items that fail. Just like humans they worked perfectly when new but with time slight flaws or imperfections can lead to failure in time. As to whether those parts were slightly stressed is difficult to understand and ends up as guesswork given that only some items fail in any one part of a circuit. Like you I wonder why but have long ago accepted that in many cases the answer is not to be had.
Do you have memory dumps of your brain available in Patreon? I'm trying to get used to all the gearporn that you show. I actually don't know what the 2/3 of those devices do.
Isn't it dangerous to play with x-rays on programmed devices/components?
So the question is: what makes those components to fail?
Time.
OMG, these things are still like 10-20k$ even on ebay, how to you get them so cheap?
RF shields looked better in the past, like the big milled shield on HP 3585A input mixer/filter, injection molded aluminium parts nowadays.
He is buying them as broken, which brings the price down. Still even broken they will cost probably around 5k$. Shariar has a lot of Patreon supporters, and that is how he is able to finance all that. These money are really well spent.
@@adamturowski3765
Yes and selling a working machine will finance the next.
211 mhz = cat ;)
Fu fu first, yo!
I hate all instruments that are non-PC shape with PC OS like Windows .....