Video Teardown and Repair of an HP 8648C Synthesized Signal Generator - Page 1
Forum section: electronics / repair

author: Hugoneus
author_rank: Frequent Contributor
timestamp: October 07, 2012, 12:07:02 pm
content: In this episode Shahriar attempts to repair an HP 8648C Synthesized Signal Generator from a dumpster dive. The cause of failure is investigated and traced. Alongside the repair efforts, the internal construction and components of the synthesizer are also presented. Various component teardowns are shown and described including the structure of the VCO used in the generator assembly. The functionality of the repaired unit is verified using an Agilent Power Meter and Rigol Spectrum Analyzer. Finally, the overall unit block diagram is presented and the principle of operation is described in detail.Link to the video:http://thesignalpath.com/blogs/2012/10/07/teardown-and-repair-of-an-hp-8648c-synthesized-signal-generator/Link to other videos:http://www.TheSignalPath.com

author: robrenz
author_rank: Super Contributor
timestamp: October 07, 2012, 06:03:07 pm
content: Very nice Video. Looking forward to that PLL video.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: October 07, 2012, 07:03:40 pm
content: I want to point out that I went back and replaced the glue with temperature rated silicone just in case.

author: saturation
author_rank: Super Contributor
timestamp: October 08, 2012, 08:23:09 pm
content: Most wonderful teardown and detailed analysis! Very very excellent!

author: free_electron
author_rank: Super Contributor
timestamp: October 08, 2012, 09:02:59 pm
content: U21 and U22 are NOT transistors but MMIC's (monolithic Microwave integrated circuit ) most likely from Avago or mini circuits. Probably a MAR-1 or similar.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: October 09, 2012, 01:18:20 am
content: Quote from: free_electron on October 08, 2012, 09:02:59 pmYes, they could be. They are usually no more than two or three transistors. However, their function is clear in this case.

author: free_electron
author_rank: Super Contributor
timestamp: October 09, 2012, 01:46:25 am
content: MMIc's are a bit more complicated than a single transistor. Especially since they are gain flat over their specced bandwidth... not something you pull off with a single transistor..Anyway , the can you opened is not the interesting one... rip the oscillator apart . That is a whole different can of worms....there's three master oscillator depending on the band you are working in. They use PIN diodes to switch them around.The DB9 is the power distribution and control signals.The nice thing about these machines is that the base platform is the same. The three plugins and the optional YIG define what you can do with it.You can simply swap one of the cans to alter it.oh, and don't take apart the attenuator.... you'll never get it together again ( and working right )

author: Hugoneus
author_rank: Frequent Contributor
timestamp: October 09, 2012, 02:36:43 am
content: Quote from: free_electron on October 09, 2012, 01:46:25 amI am well aware of these issues. I design circuits and systems operating at 100GHz and 100Gb/s. I also said a few transistors, which I believe the MAR-1 has only two.QuoteIt is no less interesting or complex than the other three. The Reference module has a fixed oscillator. The output board has the mixers and switches. The module that I opened has the tuneable synthesizer (and thus another oscillator).QuoteThere is actually only two. A fixed one at 1GHz (LO) and the adjustable one between 500MHz ~ 1GHz. Combination of dividers, mixers and multipliers generate all the frequencies.QuoteI am not sure what DB9 is. The power (DC power) distribution and the controls signals as well as the low-frequency modulation signals are generated from the motherboard.QuoteAll the 8648 series synthesizers use the same main three modules. The output module differs depending on the model. I don't believe this series supports a YIG oscillator.QuoteThe RF switches inside this attenuator are self contained, the passives are most likely printed on a ceramic board.

author: TerminalJack505
author_rank: Super Contributor
timestamp: October 09, 2012, 02:46:00 am
content: Lucky bastard! Nice find.I had a good laugh when the mystery of the missing capacitor was solved. Its absence didn't make any sense. It's like it just vanished. But then there is was the whole time, right under our noses.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: October 09, 2012, 02:55:42 am
content: Quote from: TerminalJack505 on October 09, 2012, 02:46:00 amI felt the exact same way.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 09, 2012, 03:41:09 am
content: shariar, can you provide a download button at your site because youtube algorithm sux they separate the movie into chunks i cant save in my harddrive. your consideration is much appreciated thank you!

author: Hugoneus
author_rank: Frequent Contributor
timestamp: October 09, 2012, 03:44:16 am
content: Quote from: Mechatrommer on October 09, 2012, 03:41:09 amOk, I will think of a way to provide a link for you to download them. The files are quiet large and I don't have much hosting capacity. As you know my site does not generate any revenue so all the costs are out of pocket.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 09, 2012, 03:56:55 am
content: isnt there a way we can download direct from youtube without looking at it first? i hate to watch jerky movie online. so what i did, i muted it until it got completed, but when i tried to replay, it started to download from zero again, to avoid that i looked at cookies folder it mutilated into pieces. F**K to the programmer doing that

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 09, 2012, 04:06:41 am
content: Quote from: Hugoneus on October 09, 2012, 03:44:16 ami dont know whats you profession but i believe you can do it just as Dave if you want to, as a first step you need to figure out why i cant register into your site

author: robrenz
author_rank: Super Contributor
timestamp: October 09, 2012, 04:16:38 am
content: I find that if I pause the video and let it buffer until all most complete then hit play before the grey buffer indicator reaches the end it will play the whole video. YMMV

author: SeanB
author_rank: Super Contributor
timestamp: October 09, 2012, 04:42:06 am
content: Firefox addon called Flashgot works for me. It downloads the whole file to a chosen directory.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: October 09, 2012, 05:15:50 am
content: Quote from: Mechatrommer on October 09, 2012, 04:06:41 amI did not know that you could not register. Do you mean to the site's forum? Can you please let me know what it says?

author: firewalker
author_rank: Super Contributor
timestamp: October 09, 2012, 07:16:03 am
content: You must be really stupid to dump such a piece of gear.Alexander.

author: Tepe
author_rank: Frequent Contributor
timestamp: October 09, 2012, 11:40:34 am
content: Quote from: firewalker on October 09, 2012, 07:16:03 amNot really, because first you would have to spend a little time doing what the OP did and then you would have to establish that the machine is still reliable which may entail having it calibrated, etc. And most likely it was written off a long time ago as a result of depreciation. The rational behavior for a business might be just what was done: Throw the thing in the dumpster.

author: jeremy
author_rank: Super Contributor
timestamp: October 09, 2012, 11:44:09 am
content: Quote from: firewalker on October 09, 2012, 07:16:03 amssshhhh! Don't ruin it for the rest of us.

author: firewalker
author_rank: Super Contributor
timestamp: October 09, 2012, 11:48:45 am
content: Quote from: Tepe on October 09, 2012, 11:40:34 amGive it away, don't throw it away!Alexander.

author: free_electron
author_rank: Super Contributor
timestamp: October 09, 2012, 02:40:42 pm
content: The cans are different depending on certain options and depending if it is an a b c ( there is an e too i believe). The three oscillator is on the 8647a , so your 8647c may be different.I've repaired a couple of the rf cans that had dead oscillators. Blown tantalums fried part of the pcb.The mmics are avago made. Discontinued but you can find them on ebay.

author: Tepe
author_rank: Frequent Contributor
timestamp: October 09, 2012, 02:51:01 pm
content: Quote from: firewalker on October 09, 2012, 11:48:45 amThen you open a different can of worms. How, to whom, etc.? And you may not even be allowed to do so depending on the contract you entered into when you got the instrument in the first place. ;-)

author: Hugoneus
author_rank: Frequent Contributor
timestamp: October 09, 2012, 04:18:12 pm
content: Quote from: free_electron on October 09, 2012, 02:40:42 pmYes, you are right. Than you for your insight and discussion. I enjoyed it!

author: kg4arn
author_rank: Unknown
timestamp: October 10, 2012, 09:23:42 am
content: Shahriar,I enjoyed the video.You mentioned the thickness of the aluminum RF shielding structure.How important is the thickness for RF shielding purposes?My first impression was that it was thick so as to provide thermal inertia, thus added short term thermal stability.And that extra thickness was not as important for the RF shielding aspects.I would appreciate your assessment of the trade-offs between the thickness and the RF shielding effectiveness.Thanks

author: free_electron
author_rank: Super Contributor
timestamp: October 10, 2012, 05:55:46 pm
content: Those can's are not aluminum. The big shiny can around the board is mu-metal.The block around the local oscillator is most likely Zamac ( Zinc , Aluminum, Manganese Copper). Zamac is perfect for injection molding (which this looks like). HP / agilent used Zamac extensively in their older style chassis like for the 8116 / 8112 generators.