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Hi Jeremy,

Nice noise floor. You are still at 20dB/decade at 10Hz slope so playing with sustaining amplifier and reducing Fk might improve things a lot.

I will email you, perhaps it's getting a bit off-topic.

Leo

Thanks.

I had some free time today and experimented with a discretely designed gain block in place of the MMIC. I think I'm hitting the limits of the E5052A now but I managed -170dBc/Hz at 10kHz offset and about -178dBc/Hz for the far out noise floor. I couldn't improve on about -160dBc/Hz at 1 kHz offset. This is a slight improvement but I think the E5052A is becoming the weak link. I've seen the PN2060C phase noise analyser by BG6KHC on qsl and this looks to be an interesting piece of equipment for $849.?
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I've linked to it below.
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Welcome to BG6KHC’s website
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Has anyone got any experience of this device?

I also designed a 10 MHz LC resonator version with the aim to run the resonator at fairly high power. I've a fair bit of experience designing discrete low noise gain blocks so I replaced the noisy MMIC with a discrete BJT design and the first attempt is as below.

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I think I can improve on this by several dB by reconfiguring the output network of the gain block (to allow higher power) and also I think I can improve on the resonator if I order some better parts for the resonator. It currently manages -165dBc/Hz at 10 kHz offset but I think the next version will be better than this.

There's a lot of spurious signals below about 500 Hz and this is due to pickup in my workroom from nearby equipment. I'll try and do something about this. I don't think it is getting in via the DC power feed.

The noise floor is very lumpy once it gets below -180dBc/Hz on the E5052A and again, I'm probably exploring the limits of the E5052A again here.

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This is an LC oscillator not a crystal oscillator so the close in phase noise is relatively poor. I'm not that interested in achieving low phase noise below about a 1kHz offset but I can probably experiment with the gain block to minimise flicker noise.

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Hi all,

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Great thread, lots of useful info including suspected power supply issues on the A3.

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I recently picked up an E5052A at auction. I've worked on similar era Agilent boxes but new to this model.?

Unit was sold has having a known issue on startup. There is a strange startup message which I believe is related to the A3 DSP board:

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This happens on power up. The analyzer will then show the following runtime error and exit; it never makes it to the measurement screen:

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The first few things I did was to backup the original HDD (20 GB Travelstar) and set that aside.?

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I used the ghost factory backup image in the recovery partition to make a new hard drive, which booted just fine.?

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Same error message on power up with original FW version 2.00. Updating to 2.51 does not change anything.

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I'm convinced that the error "m_pA3drv -> Initialize()" is likely a hardware error, telling us that the A3 ADC/DSP board fails to initialize.?

This is only a guess; I see that jmr has disassembled the firmware. Your software skills are far superior to mine; maybe this error message makes more sense to you?

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What I'm working on now is to make a wiring harness so I can extend the 3 x 32 (96 position) header for the A3 ADC/DSP.?

This way I can power the board outside of the chassis and check things like power supply rails, clock distribution for the ADCs and FPGAs.?

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By the way, is the A3 board a huge hassle to remove for anyone else? The board is wedged extremely tight in my unit. I had to use a screwdriver to pry against the metal shield bolted to the board. I did it very carefully so no damage... it was impossible to remove otherwise.?

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Giving the A3 a once over with shield removed, are a few CPLDs and a tssop FLASH chip, probably for the Sharc DSP. Hopefully its not a data corruption issue on one of these factory programmed devices...?

The first thing I recommend that you do is to look at all the PSU cables in the PSU area including the big multiwire one that loops back to the motherboard.

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As a first attempt, try partially removing each connector from its header and walk it up and down a few times on its header pins to try and remove any oxidation. Do this for all the connectors in this area including the big multi-way connector that loops back the CPU area. I think this one has lots of brown wires. Wiggle and walk them all in their pins and retry the unit. It could be that you have excess voltage drop in the connections to the A3DSP board.

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Appreciate the suggestion. I reinstalled the A3 and tried cycling all the PSU connectors, including the motherboard one. I also brushed a tiny dab of Deoxit D100 on each male pin and cycled the connectors a few times.

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Unfortunately, no changes.?

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I also checked all of the power supply test points that are made accessible. All of the voltages seemed present and at a reasonable level:

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One thing I observed on the back of the A3 board are the presence of red LED. These seem to be connected to different power rails on the back of the board.

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I noticed that 1 LED was very dim and the other was not lit. These are visible with the outer cover off, through the chassis air holes where the A3 is slotted.

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The 2 LEDs in question are the bottom most ones, which are connected to the 2 TO-220 voltage regulators U18 and U19.

Not sure what the "normal" condition should be; are both normally lit when no issues are present?

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U19 is an ON semi CS5208-1. Datasheet is as follows:

Compare to U18 which is an LT1085:

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The CS5208-1 is not available anymore, but the LT1085/1084 are. As far as I can tell, these are nearly identical regulators?

The CS5208 is rated to higher currents (6V, 9A) while the LT1085/4 is tolerant of higher voltages (30V, 3/5A). However, the pinout and output divider adjustment equations are identical?

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I can get the LT1084 on Digikey. Maybe its worth swapping both U18 and U19 out with new LT1084 and seeing if anything changes?

I was able to source some CS5208-1 from Kynix. Had good results ordering obsolete/obscure parts from them before:

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Also finished designing some adapter boards to bring the A3 out of the chassis and allow for "hot" testing.?

They connect together using Samtec SFSD .050" wiring harnesses, which come in all sorts of lengths. Hopefully 24" of wire doesn't mess up signal integrity too much.?

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I just ordered parts and boards. If its successful I'll share gerbers and BOM so others can use.?

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In the mean time, does your firmware disassembly have any useful hints as to what that error means? Looks like its pointing out a particular .cpp file in the FW related to the A3.?

Also, if anyone has info on LEDs that would also be great. Wish I had a working unit to look at and compare which LEDs are lit/not lit. Of course service manual doesn't say anything.?

Figured it out.

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So the LT1084 arrived from digikey. I swapped U18 and U19 on the A3; no changes in LED state or boot up error.

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At this point, I had also removed PSU and removed PSU daughterboard, cleaned all the connectors and put more deoxit on the pins, and put it all back together.

So I'm sure it wasn't a power supply issue.

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There are 5 right angle male SMB connectors on the front of the A3 module. Two on the left are CH1 IF and two on the right are CH2 IF. The middle one is a 100 MHz clock.

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Looking at the layout of the A3, this is a clock input, as there are multiple clock distribution ICs which spread out to all the FPGAs and ADCs.

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So I put a low frequency directional coupler in the path of this clock and checked the coupled signal on a scope. No signal at all.

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I then used my signal generator to inject a 100 MHz, -20 dBm clock in manually. After that, the instrument got past the original error and booted to the measurement screen!

However, it failed nearly all of the power-on tests. Strange, since the results were mostly gibberish (no actual voltage values, lots of fails on power rails that I confirmed manually).

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I decided to investigate the lack of 100 MHz clock. This SMB cable leads back to one of two identical local synthesize modules (A4/A5). Removed both as they are identical.?

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Doing some side-by-side measurements, I noticed that there was a blown surface mount fuze on the module which was responsible for the clock.

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I traced the circuit before and after, it looks like this fuze separates a switching and linear regulator locally from the power rail coming in through the backplane. There are lots of tantalum and aluminum caps, so I did some in circuit DC measurements. No sign of a blown or failed cap, and all test points measured identically between the two.

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Of course, I don't have a 1 amp SMT fuze in this size, so I had to macgyver a 5 x 20, 1A glass fuze with heatshrink and some wire to put it in circuit.?

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Popped the modules back in and viola, its working.

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No clue why the original fuze opened, as the unit seems to run normally otherwise. All power on test points are normal and measurements also look reasonable.

Example measurement of recently OEM calibrated sig gen (E8257D UNX), seems to align with specs.

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Now have to order the proper fuze and make the repair permanent.

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Cheers,

Kevin

Glad you got it fixed!

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I did look through the program code and found references to your errors but I couldn't find an obvious cause, only ways to patch past the errors. There are some diagnostic features built into the code but I haven't really explored these and there is a debug file that gets written to if anything fails during bootup. Yours has probably overwritten with a blank file if it is working OK.

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Note that the main program code includes a simulator mode where you can install and run the program on a (Windows 2000?) PC and it simulates a fully working E5052A. It even gives a simulated phase noise response on screen that has 'moving' noise.

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However, I tried it on a couple of PCs (not Windows 2000) and it quits after a couple of seconds. This may be deliberate as there doesn't appear to be a way to manually quite the E5052 app apart from turning off the instrument. I did manage to get it to stop quitting with a crude patch but it wasn't really worth the effort.

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The pass/fail limits for the various service mode tests are stored inside a file on the HDD and I can show you where this is if you haven't already found it..

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I'm pleased you got it working, I wasn't too keen on taking mine apart again and it's packed away in storage at the moment. It isn't an instrument I will use very often, maybe a few times a year or so.

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I've got an old library plot of an E8257D PSG sig gen at 1 GHz and it agrees very closely with your plot although the vertical scaling is very different.

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I can also see the 60kHz blip from the LCD on your plot. It's inverted but it will be much more obvious (and not inverted) when you test something with lower phase noise at a 60 kHz offset. You can see it in the plot below as well.

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