Products > Test Equipment
Video Teardown and Repair of an Agilent E4433B ESG-D Signal Generator
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Hugoneus:
Dear G0HZU,

Thanks for all the great information you provided. This is exactly the kind of discussion I always hope to arise from the videos. Your point about the output impedance of the final amplifier is much appreciated. It skipped my mind at the time of the teardown to take the ALC feedback impact on the output impedance into consideration. Thanks you for that.

I agree with you that the replacement part probably has inferior OIP3 compared to the original part and that is why I tried to measure the a constellation EVM at the end of the video to make sure the result is still acceptable. I can try generating two tones also to actually measure the IM3 levels at various output levels.

A replacement part would be much appreciated if you have some. I can purchase a few from you and pay for the shipping.

As for the other suggestion for the Falcon software, it is a great debugging tool to monitor all the analog bus voltages. I have used it before but this time I thought it would be more interesting for the viewers to do a teardown. :)

I'll look at the options for you as soon as I get home.

Thank you all for your contributions.
G0HZU:
One thing to note: If you still have the original H1 part then it might be worth keeping it safe.

If the external active bias circuit has failed and the drain voltage at the device falls to 0V as in your video then maybe HP/Agilent designed the active bias to not cook the device if the active bias wasn't there. So the HFET might be OK.

So maybe the only faulty part is in the active bias circuit. But I'll see if I can find some new ones at work. It won't be until Jan 5th though because I'm on xmas holiday :)

Hugoneus:

--- Quote from: G0HZU on December 22, 2014, 08:00:47 pm ---One thing to note: If you still have the original H1 part then it might be worth keeping it safe.

If the external active bias circuit has failed and the drain voltage at the device falls to 0V as in your video then maybe HP/Agilent designed the active bias to not cook the device if the active bias wasn't there. So the HFET might be OK.

So maybe the only faulty part is in the active bias circuit. But I'll see if I can find some new ones at work. It won't be until Jan 5th though because I'm on xmas holiday :)

--- End quote ---

Great! I still have the old part... Unless my cat ate it because I left it on the table.

Enjoy your holidays!
G0HZU:
Thanks :)

I guess you could look at the other devices on that board to see how they are biased and how the bias behaves when healthy.

On my design I included an interlock that meant that the 8V feed would get switched off if the negative bias failed. This prevented damage to the HFET. Maybe HP designed an overcurrent trip on the 8V feed to do a similar thing?

I also had to make sure that the circuit behaved itself during power up and power down without stressing the SHF-0189 devices during this brief phase. In all I had to do quite a complicated design to keep the devices reliable electrically and thermally but it was worth it for the RF performance these devices deliver.
HighVoltage:
Really great repair video again.

The way you are guiding us through the steps is very easy to understand, although I have not much HF experience at all.
Thank you!
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