Video Teardown and Repair of an Agilent E4433B ESG-D Signal Generator - Page 1
Forum section: electronics / testgear

author: Hugoneus
author_rank: Frequent Contributor
timestamp: December 22, 2014, 03:09:27 pm
content: 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 Since this part is obsolete, an RFMD GaAs hybrid amplifier is used in its place.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_44More videos at The Signal Path:http://www.TheSignalPath.com

author: G0HZU
author_rank: Super Contributor
timestamp: December 22, 2014, 03:41:51 pm
content: Wow, Shahriar, that is good timingI'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 videoCan 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?

author: free_electron
author_rank: Super Contributor
timestamp: December 22, 2014, 03:44:39 pm
content: 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.

author: G0HZU
author_rank: Super Contributor
timestamp: December 22, 2014, 04:54:40 pm
content: 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

author: G0HZU
author_rank: Super Contributor
timestamp: December 22, 2014, 05:18:13 pm
content: 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.

author: G0HZU
author_rank: Super Contributor
timestamp: December 22, 2014, 05:36:04 pm
content: I had a rummage and I found an old X model amplifier I designed about 12 years ago with SHF-0189 drivers.See below for a shaky image.I followed all the design guidelines in the datasheet when designing this driver so you can see the heatsink screw and the numerous via holes. There is also a copper heat spreader directly under the PCB to keep the junction temperature of the device low. But this design of mine had to work in a very hot environmment and it was near a 10W broadband power amplifer as well...See the image below. It looks very similar and you can see that I had to use drain/gate feedback to flatten the gain over a wide bandwidth. I expect that HP/Agilent will have done similar.See also the link to a SHF-0189 datasheet. However, I suspect that the H1 devices in your E4433B date back to before the days when Stanford/Sirenza (the original device manufacturer) were bought by RFMD.http://media.digikey.com/pdf/Data%20Sheets/RFMD%20PDFs/SHF-0189(Z).pdf

author: G0HZU
author_rank: Super Contributor
timestamp: December 22, 2014, 06:07:11 pm
content: Hope nobody minds me posting up all this stuff but it would be worth looking at the HP/Agilent PCB to see if there is an active bias network on the back of the board.I have designed active bias networks for these devices and I base the design on this old app note from Sirenza. By using active bias you lose a bit on P1dB and OIP3 but it is a good tradeoff for mass manufacturing because you don't have to manually bias the device during production test.http://application-notes.digchip.com/147/147-47819.pdfMaybe your SHF-0189 got toasted because the active bias network failed (if it has one). See if you can see a similar active bias network on that Output Board. It should have a negative bias voltage at the gate. If the negative bias is not there then the device will draw several hundred mA and cook itself pretty quickly...

author: RRobot
author_rank: Regular Contributor
timestamp: December 22, 2014, 06:26:30 pm
content: That was a fantastic repair job. Thanks for posting it.

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 22, 2014, 06:37:41 pm
content: Quote from: G0HZU on December 22, 2014, 03:41:51 pmI have one with both options and I have no problem with it.1E5 High stability timebaseUN5 Multicarrier multichannel CDMAUN7 BER AnalyzerUN8 I/Q GeneratorUN9 8MB ram for I/Q GeneratorUND Dual ARB

author: G0HZU
author_rank: Super Contributor
timestamp: December 22, 2014, 07:36:28 pm
content: Hi PA0PBZ. I've sent you a PM about the options issue I'm experiencingShahriar,Getting back to the repair, the SHF-0189 was designed to provide very low distortion when driven at a level well backed off from P1dB. I'd expect it to outperform the NBB-310 in this respect because it is designed to give a much higher OIP3. So I do think it is worth trying to source an SHF-0189 if this is indeed the correct part.At the very least I can send you a used one but I might be able to find some new 'old' stock gathering dust in one of my storage areas at my place of work. They are cheap devices so you can have one for the cost of postage.I'd be wary of buying one on ebay because the various chinese copies/fakes will be out there now that this range of devices is obsolete. If I send you one it will at least be a genuine SHF-0189

author: Hugoneus
author_rank: Frequent Contributor
timestamp: December 22, 2014, 07:44:33 pm
content: 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.

author: G0HZU
author_rank: Super Contributor
timestamp: December 22, 2014, 08:00:47 pm
content: 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

author: Hugoneus
author_rank: Frequent Contributor
timestamp: December 22, 2014, 08:02:02 pm
content: Quote from: G0HZU on December 22, 2014, 08:00:47 pmGreat! I still have the old part... Unless my cat ate it because I left it on the table.Enjoy your holidays!

author: G0HZU
author_rank: Super Contributor
timestamp: December 22, 2014, 08:35:56 pm
content: ThanksI 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.

author: HighVoltage
author_rank: Super Contributor
timestamp: December 22, 2014, 08:53:14 pm
content: 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!

author: free_electron
author_rank: Super Contributor
timestamp: December 22, 2014, 09:51:48 pm
content: who , knows , maybe after traveling through the cats digestive system that part may work again..if only it were a cat-whisker diode ...

author: G0HZU
author_rank: Super Contributor
timestamp: December 22, 2014, 10:04:35 pm
content: I managed to dig out a really old Stanford Microdevices datasheet for this SHF-0189 device and it shows the Id vs Vgs vs Vds.Stanford were the company that made this device many years ago.You can see why the device will get fatally stressed if it loses the negative bias and Vgs falls to 0V and Vds is 8V. It will draw about 300mA from 8V and this will cook it. It will normally run at about Vgs = -1.3V for 100mA Id although this will vary from device to device.This is why it is wise to design in a cutout/interlock circuit for the 8V feed and I suspect that HP will have done this. It's a shame that they don't produce a schematic for this sig gen...

author: Hugoneus
author_rank: Frequent Contributor
timestamp: December 22, 2014, 11:36:32 pm
content: Quote from: free_electron on December 22, 2014, 09:51:48 pmBrilliant.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: December 22, 2014, 11:41:35 pm
content: Quote from: G0HZU on December 22, 2014, 10:04:35 pmThanks for the info. It is possible that the biasing circuit is what has died. The new device does not need the input negative biasing scheme. I can measure the IV curve of the device I took out and find out if it still works!

author: G0HZU
author_rank: Super Contributor
timestamp: December 23, 2014, 12:22:49 am
content: Probably the simplest check is to see if the gate has shorted to the drain with a DMM. Normally the device measures just a few ohms drain to source on a DMM but the gate to drain should he high impedance.If the device fails and the drain goes low Z to the gate then the device will override the biasing (active or passive) when in circuit and put a positive bias on the gate and it will probably cause the 8V feed to trip out a protection circuit as the device will take a lot of current in this faulty state.Maybe this is why you saw 0V on the drain and the gate? Because it tripped something? But I'm just guessing really...

author: Hugoneus
author_rank: Frequent Contributor
timestamp: December 23, 2014, 06:36:02 am
content: Quote from: G0HZU on December 23, 2014, 12:22:49 amDammit! I can't find the part! I knew my cat would do something to it...

author: SeanB
author_rank: Super Contributor
timestamp: December 23, 2014, 07:07:46 am
content: Look tomorrow in the litter box, it will be there somewhere............But in any case you did in testing see a negative bias then nothing, so likely it was short circuit eventually. As is you probably could leave the MMIC in there as it does provide enough gain, and for most applications does the job. Might not be perfect at edge cases, but for everything else it works.

author: bktemp
author_rank: Super Contributor
timestamp: December 23, 2014, 07:58:31 am
content: Great video! I always enjoy the teardown/repair of expensive equipment.A bit off topic, but I wonder how the IQ modulator works. A typical IQ modulator needs a 90° phase shifted signal, but how is this done in the signal generator over such a wide frequency range?

author: G0HZU
author_rank: Super Contributor
timestamp: December 23, 2014, 12:06:29 pm
content: I watched the video more closely this morning and I think I can explain why the device biasing seemed confusing during the DMM probing.At 42:53 you actually measured the gate bias at -2.1V (not the drain). The drain was close to 0V. So I think you accidentally got these measurements back to front and this caused the confusion. So I think the active bias was valiantly trying to bias off the (damaged,shorted) SHF-0189 device at 42:53, and maybe -2.1V is the most negative the bias generator can go before it hits its circuit limit and gives up. It was never going to succeed because I now think the HFET is indeed faulty.If we then fast forward to 45:50 when you remeasure the gate voltage we can see that it has risen from -2.1V to +0.2V.I think this is expected because you removed the bias choke in the drain and so there is no drain current. So the active bias circuit will raise the gate voltage to the other end of its range to 'try' to get the target drain bias current of maybe 100mA. Obviously it is going to fail because there is no DC path to the drain because the bias choke is removed and it probably hits its endstop at +0.2V gate bias voltage.So I think the active bias circuit may be healthy and it probably has an operating range of -2.1V to +0.2V at the gate.This should be more than enough range to bias a healthy HFET to the target bias current (probably 100mA) with enough range to cover the spread in device charactersitics across a large batch of SHF-0189s.The other thing I noticed was that the final HFET device at the sig gen output looks like it may have already been changed in the past as it looks like it has been hand soldered. See 28:09 in the video because Q2600 (H1) looks like it has been replaced/resoldered in the past and it also doesn't have the extra red dot on it like the other H1 devices.So maybe these devices fail quite often in these sig gens. It's a bit of a concern for me because I now have two of these 4GHz E4433 sig gens here at home. I bought the first one earlier this year and bought another one a few days ago. They can be bought quite cheaply if you are patient. I bought the first one for £780 and the second for £1000. Both have lots of options fitted and they probably cost over £20k new.

author: SeanB
author_rank: Super Contributor
timestamp: December 23, 2014, 02:15:42 pm
content: If that then at least we know you can replace some with MMIC devices with little drop in performance.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: December 24, 2014, 01:39:42 am
content: Thanks G0HZU,What you are saying is very plausible.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: December 24, 2014, 11:17:53 am
content: Shahriar,Another fine detailed video. Thanks

author: G0HZU
author_rank: Super Contributor
timestamp: January 05, 2015, 11:26:40 pm
content: Hi ShahriarI had an initial rummage through my dev parts box at work and couldn't find very many of these parts.I did manage to find 1 new unused SHF0189(Z) with the H1Z marking (this is the lead free part) and I can remove a working one from an old dev board that is the SHF0189 with the H1 marking.So I can send you two parts for the cost of postage if you still need them. I assume it will be cheapest if I send them in a slim jiffy bag by Royal Mail. This will probably be just a few dollars postage with about a 7 day delivery time. I'm not bothered if they get lost in the post so no need to pay for tracking unless you would prefer this? I'm guessing it will be about $12 with tracking for about a 7 day delivery.

author: Hugoneus
author_rank: Frequent Contributor
timestamp: January 05, 2015, 11:52:15 pm
content: Quote from: G0HZU on January 05, 2015, 11:26:40 pmThanks a lot. How would you like me to pay you? PayPal?

author: G0HZU
author_rank: Super Contributor
timestamp: January 06, 2015, 12:54:16 am
content: I've sent you a PM

author: TSL
author_rank: Regular Contributor
timestamp: April 09, 2015, 05:26:23 am
content: Hi Shahriar,Great video and very timely for me.I just picked up a 4432B ESG-D with opts 100,1E5,H99,UND for $700AUIt has the same fault indicator. I'm just about to embark on a fault finding mission to see if its the same device that failed.FYI you can buy SIRENZA new parts from UTsource here...http://www.utsource.net/ic-datasheet/SHF-0189-1906844.htmlregardsTim

author: TSL
author_rank: Regular Contributor
timestamp: April 11, 2015, 08:11:24 am
content: Hi all,Just finished repairing my 4432 and guess what ?It was the same fault that Shahriar had in his, that FET had failed. Mine thinks its a 25ohm resistor!Not having any on hand and thinking about the 2 week delay to get some from UTsource I rummaged around in my box of MMIC's and found a Minicircuits GALI-84+.The GALI-84+ has the same package and similar IP specs as the FET.Fitting it was a breeze and now the generator is fully working. Testing it against my Agilent 8935 test set shows its output and modulations within spec.regardsTim

author: G0HZU
author_rank: Super Contributor
timestamp: October 14, 2015, 09:56:00 pm
content: Sorry for the late reply but I found this thread again on google and I have a few comments about the use of the GALI 84.If you look closely at the original Agilent PCB layout/circuit with the SHF0189 there appears to be negative feedback fitted in the form of an RC circuit. It's there for various reasons and if you look back at my earlier post in this thread I also used similar feedback when I was designing with the SHF0189 many years ago.This feedback improves the SHF0189 matching (because it isn't really a 50R gain block MMIC) and also it improves the stability and also it flattens the gain across a huge bandwidth. This is very desirable for a wideband sig gen path.Without the feedback the gain will be very high at the low range of this amp (eg down at 250MHz) and this will mean the system ALC will have to work over a wider range depending on the sig gen frequency and the amp will be run harder here too.You might well get away with using the GALI 84 but you must be losing a fair bit of ALC margin at low frequencies because it has lots of excess gain at low frequencies. So there is technical risk here.IMO it's best to try finding the original part or a better equivalent that runs closer to the 8V? drain voltage of the SHF0189. The GALI 84 looks like a reasonable device to used for a quick/dirty repair but I think these sig gens deserve to be repaired bettter than this. But that's just my opinionNote that I don't know how well Shahriar got on with the free SHF0189 samples I sent to his office at Bell because he didn't respond to me after I sent them. They could have been lost in the post for all I know...

author: TSL
author_rank: Regular Contributor
timestamp: October 15, 2015, 12:54:52 am
content: G'Day,Yes - you do have a point - and personally I'd have liked to replace it with original parts too, but I wanted it for immediate work and I've not returned to the point of making it right.I should put its resolution on to the list of things to do !

author: drago
author_rank: Contributor
timestamp: October 15, 2015, 08:55:51 am
content: This signal generator deserves a proper repair. Explaining what is going on around SHF0189 is also a good material for a follow up video.

author: G0HZU
author_rank: Super Contributor
timestamp: October 15, 2015, 11:11:31 am
content: Yes, I'm not sure the GALI 84 is the right device to use because it has about 25dB gain down at 250MHz. By contrast, the original SHF0189 stage will probably be designed to only have something in the order of 12dB gain across 250-4000MHz using resistive feedback to flatten the gain to this level across this range of frequencies. Note that a feedback resistor with low self capacitance is needed in order to prevent issues with gain peaking up at several GHz. So if you refit the SHF 0189 then I think it's best to find and refit the original resistor parts if they have been removed as the stray feedback capacitance they introduce is fairly critical wrt gain stability up at several GHz. Alternative resistors may have higher self capacitance and this will cause unwanted gain peaking up at several GHz and will compromise the overall stability of the amp.So with 25dB gain at 250MHz in the GALI 84, the output of the vector modulator could be driving the GALI 84 output 13dB harder down at 250MHz. So that means the linearity may suffer and also it may cause issues with ALC control margins.

author: nctnico
author_rank: Super Contributor
timestamp: October 15, 2015, 06:43:23 pm
content: Quote from: G0HZU on October 15, 2015, 11:11:31 amI agree. When I looked for a replacement for a different HP RF generator I found the MMIC devices from Triquint had a much flatter gain/frequency response than those from Mini Circuits. With some tweaking I managed to get the frequency response to work reasonably over a wide range. However: if you can fix this generator using original parts then that is the best way to tackle this repair.

author: Mosaic
author_rank: Regular Contributor
timestamp: July 05, 2016, 08:31:21 pm
content: Thx for the link, I ordered some of those transistors as I have an 'unleveled' E4432B, options 1E5, UN8, UN9, UND, UNA, 100 I took a risk on for $600 based on Shah's youtube video.I only have 1 active 4 Ghz P6217 tekprobe though for a 3Ghz TDS694C scope. Also, was that an SMA interface used to connect to the probes fed by PCB soldered RG316?Quote from: TSL on April 09, 2015, 05:26:23 am

author: G0HZU
author_rank: Super Contributor
timestamp: July 06, 2016, 12:46:47 am
content: QuoteBe careful how you connect your test coax cables to the various locations along the RF signal path if you use a Hi Zscope. I haven't watched this video since the last time but I do recall that Shahriar had connected the Hi Z scope inputs to the signal path via lengths of coax.This isn't a very good (as in controlled/predictable) method because it will load the signal path differently for different frequencies and this can give confusing results. I guess one can argue that this method was fine because it helped find the dead part. However, this isn't how you are supposed to use RF test gear if you want to make reliable measurements because of the way the coax and scope will load the signal path 'differently' at different frequencies. At some frequencies it will load it a lot and it depends on the length of the coax and the test frequency.I recall that Shahriar seemed confused why the signal level had lots of ripple wrt frequency changes and this will be the reason. It appeared to me that he wasn't using the test gear correctly.

author: nctnico
author_rank: Super Contributor
timestamp: July 06, 2016, 12:54:36 am
content: I agree. When I worked on the RF amplifier of my E4421B I set it to frequencies between 10MHz and 70MHz to be on the safe side when it comes to reflections while doing measurements to get some ball-park figures.

author: Mosaic
author_rank: Regular Contributor
timestamp: July 06, 2016, 03:49:34 am
content: Well, a Hi Z probe will see ripple, but I don't see how a lo Z probe (coax with a 6dB pad for better matching?) will improve matters here when looking for small signals. Certainly if signal integrity was the subject a Hi Z would not be the way to go with VSWR all over the place.If I knew what levels to look for I could use the coax/pad approach either with the TDS694C or a spectrum analyzer. Too bad Shah didn't quantify the amplitude of the stages for us.As I recall anything under 250Mhz used a different signal path earlier on, so going with a sub 25Mhz signal is reasonable IF the unleveled indicator remains on with low freq. sigs.My unit hasn't arrived yet so i can't say.From a repair approach would it be simpler to pull the several RF SMD transistors from the module in question (once the coherent feed signal is alive), then measure all the bias points for correct bias and measure all the transistors out of circuit on an analyzer or using a basic jig @ say 25Mhz to 1Ghz for quantifying their function? That way all the transistors and biases are tested in one pass.I could do a custom jig to 3Ghz and use the VNA on it for the 1dB compression as a matter of interest.If all those are good then the ALC loop is suspect.

author: nctnico
author_rank: Super Contributor
timestamp: July 06, 2016, 11:00:40 am
content: In my generator the signals below 250MHz are made by mixing 1GHz with the generated signal but that part is before the final amplifier stage and after the auto leveling stage so testing the final amplifier at 25MHz is just as usefull as testing it at 500MHz to get a feel for the signal levels involved.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 29, 2017, 06:04:12 pm
content: Hi group,I realise that this is an old thread, but I thought it was a good idea to keep all the ESG-D repair information together.I have an E4432B ESG-D with options 1E5 and UN4. The symptoms are No output and UNLEVELED indicator when the RF is turned on. Having read this thread I was expecting to be change a dead amplifier in the signal chain.I have confirmed that the problem is on the A9 Output board assembly, by swapping the module from a good generator.First the board is very different to the one in the video:I have tracked the break in the signal path to the 'Burst Modulator'.I did this by soldering wires to the board and running the ESG at 270MHz and monitoring the signals with a scope and 10x probes.Here is a partial block diagram for an output board (option UN3 and UN4):And here is a picture of the 'Burst Modulator' on the PCB:I suspect that the circuit is something like this:I have confirmed that the right end of the diode string has an inductor to ground. I would expect the that the left hand end would be positive about 6V if the "burst modulator' is on.If I twist the wires together, to form a small capacitor, to bypass the 'Burst Modulator', the generator seems to work fine, except the 'Burst modulation'. The UNLEVEL indication is gone and I have output.The questions is where on the board is the 'BURST MODULATOR DRIVER'?Thanks for your help with this challenge.Regards,Jay_Diddy_B

author: nctnico
author_rank: Super Contributor
timestamp: January 29, 2017, 06:41:10 pm
content: I'd look in the block diagram where the burst modulation is coming from. A DMM with instant continuity is handy because you can swipe the probe along the pins quickly.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 29, 2017, 11:58:12 pm
content: Quote from: nctnico on January 29, 2017, 06:41:10 pmI followed this advice, and ended up in this area of the board:I reflowed some of the soldering joints and the problems have gone away !!I was lucky, I didn't need a single part, especially some of the unobtainium amplifiers.Regards,Jay_Diddy_B

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: May 14, 2017, 09:28:35 pm
content: @Jay_Diddy_B:Thanks for the insights, I have an E4433B that had the same issues, it too has the '1GG3' MMICs instead of the HFETs used on Shahriar's unit. I had tracked down the loss of power to the burst modulator, as you had, and then was stuck because of the multilayer board and not being able to flip the board over (due to the output MMIC being screwed down). I noticed that the transistor where the burst mod drive signal is sourced had a dry joint (mottled gray appearance instead of shiny silver). Also, one of the diodes next to that transistor were not properly soldered (the bead wasn't formed well). After some light rework, it seems to be stable; no more UNLEVEL errors! If I were to guess, I'd say the two toroids next to the diodes were probably shielding the diodes from IR during reflow.Thanks all!

author: TK
author_rank: Super Contributor
timestamp: September 20, 2018, 01:05:33 am
content: I got an E4422B unit with the UNLEVELED error and no output. I followed different repair tips from this and other threads. I tried the 20K resistor bypass fix and I got -30 dBm signal, but unit still showed the UNLEVELED error. I also tried reflowing the area near the BURST MOD at the same time. After I removed the 20K resistor, I got consistent -60 dBm signal with the UNLEVELED error still on the display, so the "no output" error was fixed, but signal did not go higher than -60 dBm... it goes down when I set levels lower than 0 dBm, but it does not go higher than -60 dBm even when I set any level higher than 0 dBm. The output amp is OK, if I remove it and bypass the input to the output, the output level drops by 30-40dBm. Then I tried to test the level before and after the BURST MOD section by soldering 2 pieces of jumper wires, one before the first diode, one after the last diode (this BURST MOD section is just before the output amplifier section). I set the output frequency to 50MHz, level to 0 dBm and connected the scope probe (10X)... magically the generator outputs the correct level... it even goes up to near 20 dBm and no more UNLEVELED error!!! After 2.5 GHz starts to give the UNLEVELED error again... Then I decided to remove the 2 wires, thinking the generator was almost fixed, but I get the same -60 dBm signal and UNLEVELED error... I solder the wires, no error... remove them, error... solder the wires, fixed...It is the most bizarre "repair" I have experienced... The wires are not even connected, they are not twisted... they are just hanging in the air... Only 1 wire doesn't fix the problem, I need to have both wires soldered

author: edpalmer42
author_rank: Super Contributor
timestamp: September 20, 2018, 02:42:59 am
content: Transmit and Receive antennas?Try soldering a capacitor between the open ends of your wires.Ed

author: syau
author_rank: Frequent Contributor
timestamp: July 16, 2020, 03:07:43 am
content: Quote from: TK on September 20, 2018, 01:05:33 amSorry for digging out this old thread, my unit has the same issue and I am finding a way to fix it (besides soldered 2 wire)

author: Bud
author_rank: Super Contributor
timestamp: July 16, 2020, 03:44:46 am
content: I fixed mine by washing the board with isopropyl and a toothbrush. While it was also a bizarre fix, my speculation was the fault could had been caused by conductive dust or tin whiskers. The unit operates flawlessly ever since.

author: syau
author_rank: Frequent Contributor
timestamp: July 16, 2020, 10:02:56 am
content: Quote from: syau on July 16, 2020, 03:07:43 amFixed by replacing the Q772 with MMBT3906LT1G and CR771 with MMBD1201.

author: TK
author_rank: Super Contributor
timestamp: August 11, 2020, 06:01:50 pm
content: Quote from: syau on July 16, 2020, 10:02:56 amIt worked for me as well, no more UNLEVELED error!

author: syau
author_rank: Frequent Contributor
timestamp: November 08, 2020, 11:14:44 am
content: Anyone managed to “adjust” this unit without using the Agilent software ? The reason for asking is my unit have 4dbm lost on 4GHz.

author: syau
author_rank: Frequent Contributor
timestamp: November 09, 2020, 09:36:16 am
content: Quote from: syau on November 08, 2020, 11:14:44 amReplacing the RPP didn’t help but bypassing it with semi rigid did

author: Miek
author_rank: Regular Contributor
timestamp: April 17, 2024, 11:38:38 am
content: Just to chime in with another data point, I recently repaired an E4433B that was showing "unlevel" and no output. After probing along the RF path on the output board I found a lot of loss along the burst mod diodes and only around 4.2V bias across them. Replacing Q772 fixed it for me too!