Products > Test Equipment
Video Teardown and Repair of an Agilent E4433B ESG-D Signal Generator
Hugoneus:
In this episode Shahriar repairs an Agilent E4433B ESG-D Synthesized Signal Generator. This 4GHz unit shows the "UNLEVEL" error for all frequencies and at all output power levels. After a close look at the system block diagram the fault is traced to the main Output RF board.
The Output RF board is equipped with various amplifiers, electronic attenuators, I/Q mixers, heterodyne paths and final PA. By using soldered SMA cables to various points in the signal path, the fault is traced to an internal amplifier chain which is likely made of a MESFET or JFET transistor. Since this part is obsolete, an RFMD GaAs hybrid amplifier is used in its place. The biasing network and matching networks need to be modified to accommodate this change. The repaired unit is then verified for functionality and performance by measuring a QAM constellation output signal.
Watch the video here: [1 Hour]
http://youtu.be/RSCGAY5z_44
More videos at The Signal Path:
http://www.TheSignalPath.com
G0HZU:
Wow, Shahriar, that is good timing :)
I've just bought one of these here in the UK for £1k. I'm going to sit down with some mince pies and watch your video :)
Can I ask what options yours has? Mine seems to have an issue with the options fitted to it. It arrived a couple of days ago in a bit of a state in terms of the way the HW options were (not correctly) installed on the user interface. I've spent the last day or so trying to reinstall the UND, UN8, H99, 1E5 and 100 options on the front panel interface in order to activate them.
It detects the option hardware as being there but it gives a clash if I try and install both UND and UN8 together. I don't suppose you know if UND overrides UN8? The various UND/UN8 installer guide documents from Agilent don't make this clear.
I can get the UND dual arb generator to work OK and the various features of UN8 seem to be there without installing UN8. But it seems odd to see UN8 as not selected/installed on the UI.
Does yours have both UN8 and UND?
free_electron:
this series of machines frequently suffers from this problem.
it's almost always the unlevel error.
i have the adjustment software for these machines. you need an agilent gpib adapter and the agilent i/o library. then you can run the 'falcon' software and set the machine in test mode and do all kinds of self-cal procedures.
G0HZU:
I'm currently watching the video and I have a comment that might clarify things at 26:50.
The reason the two parallel 100R resistors are there is to define the output impedance of the generator at 50 ohms. If you look closely you will see that the ALC detector tap point is immediately before these two resistors. It sits snugly before them.
Because the ALC detector is part of a feedback loop then the impedance at this detector tap point will be close to that of a voltage source. i.e. the impedance at this point (within the bandwidth of the ALC feedback system) will be extremely low (close to zero?) because of the nature of the feedback. So you have to fit a series 50R resistance after this point to set the source impedance of the generator to 50 ohm.
This ALC + series 50R resistor technique has been commonly used on signal generators for about 50 years (possibly more?) and I think it is used in all of the RF signal generators I have here from various manufacturers :)
G0HZU:
OK I'm a bit guilty of skimming the video (I ate the mince pies too quickly) but I think I can advise you about the amplifer device that failed in that generator.
It looks to me like an old school HFET. i.e. a heterostructure FET.
I have used the old Stanford/Sirenza/RFMD SHF-0189 (and the 0289 and 0589) many times as a driver amplifier for broadband systems and the 0189 has an H1 logo on it. So it looks like a good match. However the gain of the device is quite high at LF and I always used feedback to flatten the response.
I can see if I can find some at work if you would like one? I have the 289 and 589 devices here and I probably have a few 0189s but they will be fitted to a dev board. I think the 289 and 589 are now obsolete but maybe the 0189 is still available.
One thing to note with the 0189 is that it needs a negative bias voltage. Sometimes this is provided with an active bias circuit. If this active bias circuit fails then the device will cook itself without a negative bias at the gate pin. They are quite fragile and the specs on these devices got derated on the datasheet over the years. eg there was a change to reduce the recommended Vdd to 7V from 8V on some devices in this series. Also, the MTBF is heavily reliant on a decent layout with good thermal paths (lots of via holes). Without this the device will not be reliable in the long term.
Can you take an ultra closeup of the H1 device? I'll have a look if I have a SHF-0189 here to compare.
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