Video Teardown and Repair of an HP 8648C Synthesized Signal Generator

[Hugoneus]

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

[robrenz]

Very nice Video.  Looking forward to that PLL video.

[Hugoneus]

I want to point out that I went back and replaced the glue with temperature rated silicone just in case.

[saturation]

Most wonderful teardown and detailed analysis!  Very very excellent!

[free_electron]

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.

[Hugoneus]

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.

Yes, they could be. They are usually no more than two or three transistors. However, their function is clear in this case.

[free_electron]

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 )

[Hugoneus]

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..

I 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.

Anyway , the can you opened is not the interesting one... rip the oscillator apart . That is a whole different can of worms....

It 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).

there's three master oscillator depending on the band you are working in. They use PIN diodes to switch them around.

There 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.

The DB9 is the power distribution and control signals.

I 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.

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.

All 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.

oh, and don't take apart the attenuator.... you'll never get it together again (and working right).

The RF switches inside this attenuator are self contained, the passives are most likely printed on a ceramic board.

[TerminalJack505]

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.

[Hugoneus]

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.

I felt the exact same way.

[Mechatrommer]

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!

[Hugoneus]

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!

Ok, 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.

[Mechatrommer]

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

[Mechatrommer]

As you know my site does not generate any revenue so all the costs are out of pocket.

i 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

[robrenz]

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

[SeanB]

Firefox addon called Flashgot works for me. It downloads the whole file to a chosen directory.

[Hugoneus]

As you know my site does not generate any revenue so all the costs are out of pocket.

i 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

I 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?

[firewalker]

You must be really stupid to dump such a piece of gear.

Alexander.

[Tepe]

You must be really stupid to dump such a piece of gear.

Not 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.

[jeremy]

You must be really stupid to dump such a piece of gear.

Alexander.

ssshhhh! Don't ruin it for the rest of us.

[firewalker]

You must be really stupid to dump such a piece of gear.

Not 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.

Give it away, don't throw it away!

Alexander.

[free_electron]

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.

[Tepe]

Give it away, don't throw it away!

Then 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. ;-)

[Hugoneus]

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.

Yes, you are right. Than you for your insight and discussion. I enjoyed it!

[kg4arn]

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