Teardown & Repair of an Agilent 53152A 46GHz Microwave Frequency Counter - Page 1
Forum section: electronics / testgear

author: Hugoneus
author_rank: Frequent Contributor
timestamp: July 05, 2017, 01:39:33 am
content: You can watch the video here: [42 Minutes]youtu.be/qAmAd8QfsMgMore videos at The Signal Path:http://www.TheSignalPath.com

author: bktemp
author_rank: Super Contributor
timestamp: July 05, 2017, 07:45:50 am
content: I usually really enjoy your great videos and have learned so much about RF and microwave stuff.But this video was a bit dissapointing. It was obvious you have not much experience with repairing a SMPS. Nothing wrong with that, you can't be an expert on every field. I am neither a SMPS expert, but if you have done a couple of repairs, you know the typical symptoms and what is causing them.Therefore for me watching this video was a bit annoying, because you made quite some mistakes and repeated them over and over again.Unfortunally the TL384x datasheet does not show a typical circuit, but a datasheet from a different manufacturer has one:If you compare this to your circuit you see the component you have identified as a 15V zener diode is actually a rectifier diode providing the 15V power supply to the TL3842 when it is running. You measured 15V across it, because it is connected to the capacitor on one end and to GND via an auxiliary transformer winding. If you had replaced it with a new 15V zener diode it probably would have failed immediately.In this schematic there are two diodes in series, in your circuit there was one diode and a series resistor. But except from that it is almost identical.From this schematic you can also see why the 15V rail was pulsing:The capacitor had almost no capacitance left, so as soon the SMPS controller started, the voltage collapsed and had to be recharged by the high value startup resistor (another component that often fails aside from the capacitor you had to replace).If this startup resistor has failed, the mains capacitor will stay charged for quite some time (sometimes for days if there is no other discharge resistor). So be careful when handling a SMPS pcb even when the power is removed!A pulsing voltage is caused by either a dead capacitor or by a short on the output: If the output or one of the rectifier diodes is shorted, there is no voltage on the auxiliary winding providing the operating voltage for the SMPS controller.If you had shown this schematic, it would have really helped you and everybody watching this video to understand how the SMPS actually works.By the way: A multimeter is usually the wrong tool for debugging a SMPS, because they often operate only briefly before shutting down and restarting again. A multimeter gives only avarage voltages, therefore you only know if it is working correctly or not, but you get no informationg about what is causing that behaviour.Please excuse if this sounds harsh. I just want to give you some honest feedback what I think about your videos and help you to improve them (in most videos there is nothing to improve).So my suggestion would be, when repairing a SMPS look at datasheets and application notes of the SMPS controller for a reference design not only at the block diagram, because most many manufacturers copy that almost exactly.At the end of the video, you could have made a quick measurement showing the startup of the SMPS controller by looking at both the voltage and the gate signal. This hasn't much to do with the repair at all, but since you had shown and explained the internal operation of the SMPS controller, showing the actual operation being as expected would have completed the excursion into that.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: July 05, 2017, 12:20:36 pm
content: Quote from: bktemp on July 05, 2017, 07:45:50 amI have done done a few SMPS repairs here and there, everyone takes a different approach. But to say that I made quite some mistakes and repeated them over and over again...QuoteI in fact did remove the diode and measure it on my SMU and it is a Zener diode with 16V Zener voltage at 10mA, it just didn't make it to the video.QuoteIsn't that exactly what I demonstrated and talked about in the video? I specifically mentioned the reason why the supply was not stable and showed through measurement that the old capacitor was faulty.QuoteI have mentioned this every time I have repaired a SMPS and in this video I specifically mention it again and show how to safely discharge it.QuoteI have shown this in one of my videos and even diagnosed it simply by listening to the noises the supply makes trying to start.QuoteAre you sure you watched the video?Did I not move onto a scope and showed the dynamic behavior of the power supply on the scope once the usefulness of the multi meter was limited? You are preaching to the choir.QuoteYou said I made many mistakes and repeated them over and over again. I don't think that I did.QuoteI have done that in some of my other videos.QuoteI showed the gate voltage of the MOSFET after the repair was done and explained the PWM. I did in fact show all this!

author: TheSteve
author_rank: Unknown
timestamp: July 05, 2017, 04:28:34 pm
content: I had never seen a planar crown connector before, it's always nice to learn something new. Thank-you for the video!

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 05, 2017, 06:35:05 pm
content: That is actually an interesting dual use of that zener, it only uses the zener functionality to limit the voltage when the smps is in startup mode, and once it runs it is used both for rectifying and zener.The fact that your low-Z measurement was ok after the smps was working again is not directly because of the replaced cap, the cap has to store enough energy to make the ic start up and have the transformer take over creating the VCC and then it of course delivers enough energy not to have it collaps using the low-z measurement. Anyway, another successful repair but I hoped you would have showed a bit more of the actual counter circuits.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: July 05, 2017, 06:41:33 pm
content: Quote from: PA0PBZ on July 05, 2017, 06:35:05 pmI promise to show more of it when I do an upgrade of it. The video was running long and I needed to post it and move on.

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 05, 2017, 06:46:41 pm
content: Quote from: Hugoneus on July 05, 2017, 06:41:33 pmI'm the last one to complain about you posting a video of course

author: HighVoltage
author_rank: Super Contributor
timestamp: July 05, 2017, 08:24:08 pm
content: Very nice repair video again, thanks so much.And yes, I am looking forward to an upgrade video as well.These Agilent 53152A instruments go for $10 k on ebay !Unreal!You got a good deal.

author: technogeeky
author_rank: Frequent Contributor
timestamp: July 05, 2017, 09:04:49 pm
content: My favorite part was when you opened up the chassis and all I saw was the metal floor of the chassis, and the few parts I immediately recognized as power supply and filtering.My first reaction was: he's been robbed! Someone shipped him a power supply in a box!My second reaction was: how the hell did he make a 40+ minute video out of that?I finally told my brain to shut up, that you know what you're doing, and it's probably under some shielding or something I couldn't see. I still didn't guess it would be on the underside.Thanks as always!

author: TheSteve
author_rank: Unknown
timestamp: July 05, 2017, 09:21:47 pm
content: It will be interesting to see the RF front end in detail. I just bought a 53147A which is a 20 GHz version of this counter that has a power meter and DVM built-in. I wonder how different the 20, 26.5 and 46 GHz versions are.

author: MadTux
author_rank: Frequent Contributor
timestamp: July 05, 2017, 09:32:25 pm
content: Quote from: HighVoltage on July 05, 2017, 08:24:08 pmSold ones are more like 1k$. These 10k$ listings are the insanely priced ones that most likely won't ever sell for that price.Still quite a lot of money to gamble with, because you never know wether the previous owner has let the magic smoke out of the unobtanium microwave magic frontend

author: rx8pilot
author_rank: Super Contributor
timestamp: July 05, 2017, 09:52:04 pm
content: Quote from: TheSteve on July 05, 2017, 04:28:34 pmI had never even heard of that connector, much less seen one or used one.Quote from: bktemp on July 05, 2017, 07:45:50 amI design power electronics and have repaired quite a few commercial power supplies, I was not offended by the flow of the repair at all. If you handed that supply to 100 people, they would all take 100 different approaches to the problem. That is exacerbated by the effort to create a video in the mean time, especially when the real goal is to get to the counter. The best part of his approach is the focus on safety - so many people just dive-in and start poking away without much thought of death or blowing their fingers open.Personally, I like seeing the different approaches people take and the reactions to various issues and observations. It also appeared that Shariar was trying to keep the repair tools simple - hence the DMM and cheap ESR meter until he was essentially forced to fire up the scope to see the dynamic behaviors.

author: electr_peter
author_rank: Unknown
timestamp: July 05, 2017, 10:18:02 pm
content: As mentioned in the video, likely failure mode was failed fan. Internal PSU parts overheated without forced air flow, this accelerated drying up of capacitor which supplied power to SMPS controller.How much power does counter draw from mains? Could you check temperatures of SMPS and other parts of the board with thermal camera/thermometer? I am curious, because counter does not look like it uses a lot of power.If equipment has a fan, then a) fan is probably really needed and b) if broken fan is not repaired, some parts can be damaged. It seems that failed fan should trigger a repair or check.Nice to see that PSU is a separate module and can be easily replaced (or repaired). Modularity made debugging much easier (in contrast to single PCB solution).

author: edpalmer42
author_rank: Super Contributor
timestamp: July 05, 2017, 10:26:23 pm
content: Quote from: technogeeky on July 05, 2017, 09:04:49 pmI had the same thought. The power connector hanging in mid-air certainly added to the confusion.Ed

author: Macbeth
author_rank: Super Contributor
timestamp: July 05, 2017, 10:44:59 pm
content: I enjoyed this, even though it was really a PSU module repair rather than the Agilent gubbins. I have to admit once I found the PSU wasn't working I would have just disconnected it and fired up +/- 15V and +5V on my DP832 and confirmed all was well before going in for the PSU repair

author: rfeecs
author_rank: Frequent Contributor
timestamp: July 05, 2017, 10:48:43 pm
content: I went back and scanned your previous HP/Agilent frequency counter video, TSP #35. At the end, you speculate how the harmonic sampler worked.There's a great old HP Journal from 1978 dedicated to the HP5342A that describes a very similar sampler, and also goes through lots of detail on how the frequency counter works:http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1978-05.pdfOf course things have changed a little since 1978. It will be interesting to see if your new model is any different.

author: texaspyro
author_rank: Super Contributor
timestamp: July 06, 2017, 01:34:43 am
content: Quote from: Macbeth on July 05, 2017, 10:44:59 pmSame here... and if the counter worked I'd bodge in something like a $20-$30 Meanwell supply and be done with it. Life's too short to waste on fixing old SMPS supplies that can easily be replaced by modern equivalents. By the time you fix the issues and re-cap the supply you're out a lot more money and time.I've dropped lots of Meanwells' in place of of the Power Ones used in old HP (and other) gear. The Power Ones are still available but cost $400 new... for a 50 watt switcher! Last month alone I replaced three failied Power One supplies (two in HP GPSDOs and one in a rubidium oscillator). The pinouts on the Meanwell align with those on the Power Ones so I didn't even need to modify the power cables. Alas, sometimes form factor issues make repairing the old supply necessary.

author: ruairi
author_rank: Frequent Contributor
timestamp: July 06, 2017, 02:30:21 am
content: Guys, can we acknowledge the fact that Shariar has a day job and does these videos to teach people? He is not looking for the quickest route to getting a working unit, he already has a stocked lab and I'm sure an even more impressive set up at his day job.The point of these videos is to teach the logical thinking and methodology of fault finding so people like me can learn.

author: technogeeky
author_rank: Frequent Contributor
timestamp: July 06, 2017, 07:08:56 am
content: Quote from: ruairi on July 06, 2017, 02:30:21 amHe works at Bell Labs. It's safe to say he routinely many pieces of equipment worth more than the value of our entire net worth.And I totally agree with you. It's about the journey and not the end result. It'smoreinteresting to see someone like him stumbling and bumbling around, not less interesting. Though in this case, I disagree with the premise that he did stumble and bumble.As always, Shahriar -- keep it up man. I love your videos!

author: Hugoneus
author_rank: Frequent Contributor
timestamp: July 06, 2017, 02:07:45 pm
content: Thank you all.It is a constant battle to balance time between various activities in life.That will never change!Let's hope the next repair will have a more exciting problem!And again thank you for all the Patreon supporters. You make it possible.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 06, 2017, 03:49:11 pm
content: Quote from: Hugoneus on July 06, 2017, 02:07:45 pmEven if it does not, please keep sharing these videos, because I always learn something from you steps.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: July 06, 2017, 04:01:10 pm
content: I appreciate the fact that you took the time to show the troubleshooting process. Made for a much better repair than just going in and recapping the PS.