HP3577A 5Hz-200Mhz VNA Teardown

[sixtimesseven]

Yesterday the postman delivered another boat anchor to my dorstep - A HP3577A VNA with (75Ohm  S-Parameter Test Kit).

Teardown photos:

• HP3577A / HP35677A/B S-Parameter Test Set
  https://www.flickr.com/photos/154275690@N07/albums/72157699120602134
  

The thing looks a bit beaten and is full of dust but it seems to work fine at first glance.
Confidence test fails at item 6a, "Receiver impeadance test" The relays seem to switch fine between 50/1M and the attenuators switch fine for both ranges. Signals comming trough a 20dB attenuator look reasonable as well. Might just be an adjustment problem...

Couldn't resist to take it apart a bit. Also the front panel boutons are a bit sticky and I would really like to get them running smooth again. Also I'm probably going to switch out the CRT with a NewScope-5 LCD.

Update: LCD ordered and switches cleaned with WD-40 Contact Cleaner. They work great now. I also installed the Sanyo fan (see link below), temperatures at the heatsink stay the same for me and the noise went down from "jet engine" to anoyingly loud oc desktop pc.

Update II:
New Scope LCD is terrific. Really nice kit and nice LCD. A bit pricy but worth it in my opinion.

Interesting links:

• Original fan datasheet (Muffin MD24B2):
  https://www.jameco.com/Jameco/Products/ProdDS/2215478.pdf
  
• Sanyo replacement fan, 39dB:
  https://www.mouser.ch/datasheet/2/471/San_Ace_120WP38_E-1286779.pdf
  
• Good Service Manual scan for 12.50$, part number 03577-90010:
  http://artekmanuals.com/manuals/hp-manuals/
  
• NewScope-5 CRT to color LCD conversion
  http://simmconnlabscom.ipage.com/store/page4.html
  
• How to clean sticky switches:
  http://www.rbarrios.com/projects/HPSWITCH/
  

[Johnny10]

I keep losing auctions on this unit.
Nice buy.
I bought an S-Parameter last month thinking I was going to win an auction on a broken 3577 unit.
Nope!

I will keep trying.

Like your photos

[sixtimesseven]

I keep losing auctions on this unit.
Nice buy.
I bought an S-Parameter last month thinking I was going to win an auction on a broken 3577 unit.
Nope!

I will keep trying.

Like your photos

Well the seller put it in for 1499$ so I made him an offer for 900$ and he accepted so

I cleaned out all some of the dust from where I could get to it, removed the two logic boards and took some more pictures -> See Flickr: https://www.flickr.com/photos/154275690@N07/albums/72157699120602134


I also wanted to backup the firmware but the beancounters at HP have decided not to put in sockets for the ROM IC's 

Now I'm just waiting on my N to SMA and N to BNC adapters to do some measurments. In the meantime I will probably have a look at the S-Parameter test set...


 

[precaud]

The thing looks a bit beaten and is full of dust but it seems to work fine at first glance.

Well I'm sorry to hear that. I have three 3577A's waiting for me to troubleshoot/repair and I was looking forward to you doing the same in advance    All of mine have non-trivial issues, unfortunately.

(j/k of course... nice that yours mostly works fine!)

Couldn't resist to take it apart a bit. Also the front panel boutons are a bit sticky and I would really like to get them running smooth again.

Easy fixes once the front panel is disassembled.

Also I'm probably going to switch out the CRT with a NewScope-5 LCD.

Huge improvement. As my eyes age, that small crt becomes increasingly difficult to live with. I need to keep a magnifier handy.

Interesting links:
-Original fan datasheet (Muffin MD24B2): https://www.jameco.com/Jameco/Products/ProdDS/2215478.pdf

50dBa ! That's one noisey fan! The fan noise and crt are what keeps the 3577A (and 3562A) off my bench. Lovely instruments crippled with noisey fans and hard-to-read crts.

The Achilles heel of the 3577A appears to center around the input relays. That was the major design change between A and B versions, a redesigned front end using different relays.

[sixtimesseven]

50dBa ! That's one noisey fan! The fan noise and crt are what keeps the 3577A (and 3562A) off my bench. Lovely instruments crippled with noisey fans and hard-to-read crts.

I probably just install a quiet 12V PC fan with a 24V converter and test with the thermal cam if the 80 CFM are enough without the CRT heating the instrument.

The Achilles heel of the 3577A appears to center around the input relays. That was the major design change between A and B versions, a redesigned front end using different relays.

Do you already have some with that issue? I'm still waiting on Artek to get me the service manual so I have no idea yet what these relays are, but are they replacable at all?

[precaud]

I probably just install a quiet 12V PC fan with a 24V converter and test with the thermal cam if the 80 CFM are enough without the CRT heating the instrument.

I look forward to seeing your results. Since you've been inside the unit, I think you can feel that most of the heat comes off the various PCBs, and it takes some pressure to get air to circulate among them all. I'm doubting if a standard PC fan will be sufficient.

Do you already have some with that issue?

Yes, two of the three.

I'm still waiting on Artek to get me the service manual so I have no idea yet what these relays are, but are they replacable at all?

Replaceable, yes. Still being made, no. They were small metal-can ones made by Teledyne, the 412 series, if I recall correctly. Pull an input board and have a look.

Other HP instruments from that era (DSO's, logic analyzers  with digitizer boards) used similar relays, so its possible they may be a good source of parts if we can establish compatibility.

[rx8pilot]

I got one of these for $200 a while back - would not boot. It was the EEPROM's which I replaced with a fresh flash and it booted up.  A few days ago the big filter caps on the power supply failed - so I replaced those as well. I have done all the usual tests and it appears to be functioning as expected.

The problem is....I still don't really know how to use it. Joining this thread to learn something.

[precaud]

I got one of these for $200 a while back - would not boot. It was the EEPROM's which I replaced with a fresh flash and it booted up.  A few days ago the big filter caps on the power supply failed - so I replaced those as well. I have done all the usual tests and it appears to be functioning as expected.

Glad to hear it was an easy fix. I'm guessing it was the +5V rail caps that went? They have the most ripple current across them.

The problem is....I still don't really know how to use it. Joining this thread to learn something.

To me, VNAs are all about transfer functions. So get some devices you want to characterize and experiment. AC coupling is not an option, so be sure to protect inputs from anything with DC.

Isolation and injection transformers are a good place to start, because the 3577A has grounded inputs and output, and at some point you'll want to use a xfmr to isolate the output or insert one in a control loop. Investigate how their mag/phase responses change with load.

I use my low-freq VNAs mostly for impedance measurement. I'm a bit obsessed with Vreg output impedance and a VNA is the tool of choice for that.

[rx8pilot]

Glad to hear it was an easy fix. I'm guessing it was the +5V rail caps that went? They have the most ripple current across them.

One of the large 250V caps closer to the primary side failed short - I replaced both. They are screw terminal caps so I didn't even have to warm up a soldering iron. The EEPROM fix was quite a bit more effort to troubleshoot and execute the fix. The error message only flashes on the CRT for a second, but only when you power it up. That means the CRT is not yet displaying anything. I only noticed the message when I pressed the reset button on the processor PCB with re-boots without turning the CRT off. It allowed me to see the startup sequence. Led me right to the end of the rainbow.....

To me, VNAs are all about transfer functions. So get some devices you want to characterize and experiment. AC coupling is not an option, so be sure to protect inputs from anything with DC.

Isolation and injection transformers are a good place to start, because the 3577A has grounded inputs and output, and at some point you'll want to use a xfmr to isolate the output or insert one in a control loop. Investigate how their mag/phase responses change with load.

It looks like these can deal with 25VDC on all inputs - not quite as delicate as the HF VNA's and SA's.

That is my first attempt - an isolation transformer for testing control loop response. I am not sure how to set it up, normalize it and just get a scaler measurement of frequency response (as a first test). What is the proper setup to measure the frequency response of an isolation transformer?

I tried a few setups, but they are clearly not correct. The OUT connected to the transformer with the INPUT A in parallel - I normalized that and it is flat. Then I move the INPUT A over to the output of the transformer - but the response looks nothing like what I would expect. I did the same setup on my scope with a signal gen and it is showing that -3db should be 10hz - 6Mhz.

[Jay_Diddy_B]

Yesterday the postman delivered another boat anchor to my doorstep - A HP3577A VNA with (75Ohm  S-Parameter Test Kit).

Snip ...

Be careful with the 75  N connectors on the S-parameter test set. They will be wrecked if you mate them with 50  N connectors. The center pin is a smaller diameter on the 75 version.

I have both the 35677A 50 and the 35677B 75 test sets.

At lot of the time I use the 3577A for measuring Bode Plots on SMPS without a test set.

Regards,

Jay_Diddy_B

[precaud]

The error message only flashes on the CRT for a second, but only when you power it up. That means the CRT is not yet displaying anything. I only noticed the message when I pressed the reset button on the processor PCB with re-boots without turning the CRT off. It allowed me to see the startup sequence. Led me right to the end of the rainbow.....

Nice!

It looks like these can deal with 25VDC on all inputs - not quite as delicate as the HF VNA's and SA's.

Well I won't put DC on the inputs of mine... all three of my fixer-uppers have input stages issues, and DC is often the culprit... besides, DC shortens the useful life of relay contacts...

That is my first attempt - an isolation transformer for testing control loop response. I am not sure how to set it up, normalize it and just get a scaler measurement of frequency response (as a first test). What is the proper setup to measure the frequency response of an isolation transformer?

(Forgive if I make terminology errors, I mostly use an Anritsu VNA which uses different names for these things.)

If you want transmission response in a 50 Ohms system, or use the "Shunt-Thru" impedance technique, you need a splitter to isolate the R input from the load of the DUT. (Oh yeah, another thing you'll want to pick up at some point is a resistive splitter good to 200MHz...) An example of this is shown on p. 2-6 of the 3577A op manual.

But most often you'll want to measure transfer response from a 50 Ohm source, to include the loading effects of the DUT on the source, and into a load that you define. In the default menu, select A/R. Set inputs R and A to 1MOhm. Y the output to input R and xfmr primary. Solder a 50 or 100 Ohm variable resistor across one end of a BNC tee. That makes it easy to remove the tee to measure the R load its presenting. Maybe make some marks on the pot for certain R values. Connect the xfmr secondary to the tee, and into input A. In this setup, R=reference or stimulus, A=response. Set levels, freq range, display format, etc. Then make the sweep.

What some VNAs call "Thru", the 3577A calls "Normalize" and the Anritsu calls "X-S". At least the first two names make some sense    The basic idea is to measure the inter-channel response difference at each freq so it can be subtracted from each subsequent measurement to remove the errors. Remove DUT and connect Output to both inputs (in this situation, set at 1MOhm) and make the sweep. Then turn normalize on and voila, future sweeps will be accurate. Any change of setup requires a new Normalize sweep.

Transfer function is the same as FRA (freq resp analysis), so if you've done any of that, the same rules apply at these low freqs.

There's another clever use of the "normalize" function. Since it stores a baseline measurement, you can use it as a reference of any sort to be subtracted from other measurements. Very handy if, for instance, you want to see how mag resp and phase changes as you vary the secondary load R on a xfmr. Make the "Normalize" measurement with DUT in place at some reference R load value (say, the value of the resistor you'll be inserting in a control loop). Then make sweeps with it set at some small incremental Ohms above and below the reference value, to see how the xfmr response changes as load R varies. With Normalize engaged, it shows you the deviation from the reference, so a flat line = no change. This makes differences much easier to see than comparing overlayed curves. This will quickly show you the useable freq range of the xfmr in those conditions; the range where the mag/phase resp of the xfmr doesn't change over the load range it will encounter.

This becomes really critical when you use a xfmr at lower impedances. Unless they were specifically designed for it, the HF bandwidth of most xfmrs really narrows at lower load R's.

I tried a few setups, but they are clearly not correct. The OUT connected to the transformer with the INPUT A in parallel - I normalized that and it is flat. Then I move the INPUT A over to the output of the transformer - but the response looks nothing like what I would expect. I did the same setup on my scope with a signal gen and it is showing that -3db should be 10hz - 6Mhz.

The analyzer wasn't set up to measure A/R. And the scope isn't showing you the attenuation of the input signal by the xfmr input impedance at that secondary load R. Set it up as described earlier and try it.

Hope this helps.

[sixtimesseven]

Yesterday the postman delivered another boat anchor to my doorstep - A HP3577A VNA with (75Ohm  S-Parameter Test Kit).

Snip ...

Be careful with the 75  N connectors on the S-parameter test set. They will be wrecked if you mate them with 50  N connectors. The center pin is a smaller diameter on the 75 version.

I have both the 35677A 50 and the 35677B 75 test sets.

At lot of the time I use the 3577A for measuring Bode Plots on SMPS without a test set.

Regards,

Jay_Diddy_B

Oh I did not know that  Thank you I would have destroyed that connector. Now I have to order new adapters 

[sixtimesseven]

I probably just install a quiet 12V PC fan with a 24V converter and test with the thermal cam if the 80 CFM are enough without the CRT heating the instrument.

I look forward to seeing your results. Since you've been inside the unit, I think you can feel that most of the heat comes off the various PCBs, and it takes some pressure to get air to circulate among them all. I'm doubting if a standard PC fan will be sufficient.

Well I have to agree with that. I interpreted the pressure to be in mm not in inches. 0.28in of H2O is a lot 
Looking at Delta AFB 120 x 120 x 38 MM SERIES fans (https://www.mouser.ch/datasheet/2/632/AFB120x120x38mm-515857.pdf) the obvious replacement would be the: AFB1224HE. But I probably try the AFB1224ME which has a bit lower pressure (0.25inch) and CFM (~92)  but then the noise drop of 12dB to 38dB is worth the risk to me.

[precaud]

Looking at Delta AFB 120 x 120 x 38 MM SERIES fans (https://www.mouser.ch/datasheet/2/632/AFB120x120x38mm-515857.pdf) the obvious replacement would be the: AFB1224HE. But I probably try the AFB1224ME which has a bit lower pressure (0.25inch) and CFM (~92)  but then the noise drop of 12dB to 38dB is worth the risk to me.

Well if it works, 12dB reduction is huge and would be well worth the effort! Keep us informed, please.

[Berni]

I am just in the process of repairing one of those exact CRT modules in my HP 4145B since the NewScope5 is a bit pricy

It uses the same switches on the front panel and mine also have an inconsistent feeling. Some are soft and some are clicky. I am guessing that all of them ware supposed to be clicky but the springs got bent enough with use that they don't provide the buckling action anymore. But i prefer the soft feel of the worn out ones. I was guessing if jabbing the spring with a Flathead screwdriver would bend it enough to "break" the clicky action of the switch.

[bson]

An excellent workhorse - I use mine quite regularly, mainly for anti-imaging filters.  The nice thing about the 4-port model (I hardly ever use the S param set) is it can be used with my LeCroy active probes and the ADPPS power supply.  This way I can probe at the output of each filter stage separately, and if something odd is going on quickly track down what is invariably some mistake on my behalf.  (The same power supply also allows using the probes with counters and other instruments, just brilliant.)

Doing something about that jet turbine fan would be a huge improvement!

[precaud]

I am just in the process of repairing one of those exact CRT modules in my HP 4145B since the NewScope5 is a bit pricy

Is it just the switches, or is the display quality becoming worse too? At some point we should probably start a separate thread about repairing those modules and extending their useful life. The NewScope5 is very cool but, as you say, pricey.

I thought it would be worthwhile to mention a few things for those readers not familiar with the 3577A. Measurement-wise, it set a new standard of accuracy and performance for VNA's in its freq range. The main thing a VNA needs to be able to do is measure inter-channel magnitude and phase differences over a) a wide freq range, b) offering a wide range of suitable filter bandwidths, and c) over as wide a dynamic range as possible. These areas are where the early VNA's had limitations.

Take dynamic range. Up until then, VNAs had amplitude accuracy of +-0.5dB and phase accuracy of +-1.5º over a 60dB dynamic range (below full-scale), and only at mid-band IF's and frequencies. Max freq range was in the 10-30MHz range, and smallest IFBW was 3Hz (and not very stable). HP 3570A and Anritsu MS420 are examples of this.

The 3577A comes along and betters everything by an order of magnitude, with worst-case amplitude accuracy of +-0.08dB and phase accuracy of +-0.5º over the same 60dB dynamic range, extending it to amplitude accuracy of +-0.25dB and phase accuracy of +-1.5º over an 80dB dynamic range. And doing it at ALL IF's and frequency ranges. And offering a stable 1Hz IF and 5Hz - 200MHz useful bandwidth in the process. Remarkable.

It was an incredible work of engineering, both analog and DSP. And HP sold a ton of 'em.

The fact is, the newer VNA's don't perform any better over this same freq range. 25 years later, and it is still as good as it gets accuracy-wise.

My main beefs with the 3577A are:
: The noisey fan is almost unbearable.
: The display is too small and crowded, with poor contrast. Causes eye strain for me.
: Scattered user interface. Control grouping reflects the underlying firmware organization, not the best ease of use.
: Like most instruments from that era, its big and heavy. But it was best possible at the time.
: No built-in power splitter. A silly omission.
: No AC coupling option on the inputs. Another silly omission.
: Output and all inputs are bonded to chassis ground, requiring isolated/diff probes and/or use of output xfmr for ground-isolated low-level measurements.
: 1 Hour warmup time for stated accuracy. The instrument will spend 1/10 of its life warming up for use 

But considering that you will have to pay royal sums to find something that improves on these things, the 3577A is an incredible bargain.

EDIT: and worth mentioning... the 3577A has no firmware bugs I am aware of... I've never encountered one.

[sixtimesseven]

An excellent workhorse - I use mine quite regularly, mainly for anti-imaging filters.  The nice thing about the 4-port model (I hardly ever use the S param set) is it can be used with my LeCroy active probes and the ADPPS power supply.  This way I can probe at the output of each filter stage separately, and if something odd is going on quickly track down what is invariably some mistake on my behalf.  (The same power supply also allows using the probes with counters and other instruments, just brilliant.)

Doing something about that jet turbine fan would be a huge improvement!

May I ask which active probes you use exactly?
Thanks

[rx8pilot]

Well I won't put DC on the inputs of mine... all three of my fixer-uppers have input stages issues, and DC is often the culprit... besides, DC shortens the useful life of relay contacts...

Did you build some AC coupled adaptors? Like you, I would prefer not to test my luck! Addressing this now could save any 3577A owner a lot of trouble.

: No built-in power splitter. A silly omission.

Is it worth buying a commercial splitter for under 200Mhz or is it easy enough to DIY? Searching around for some info - they only seem difficult when the BW goes much beyond 500Mhz.

[Berni]

I have built a 3 way restive slitter before out of SMA connectors meeting in a triangle and some 0402 resistors joining them in the center and it seamed to measure just fine on the 3GHz network analyzer at work. It did get a bit wobbly past 2GHz but otherwise seamed pretty flat with a reasonably low SWR. Tho i did not measure how accurately it splits power and phase.

So for 200MHz i think a DIY one could work pretty well.

[Cubdriver]

I am just in the process of repairing one of those exact CRT modules in my HP 4145B since the NewScope5 is a bit pricy

It uses the same switches on the front panel and mine also have an inconsistent feeling. Some are soft and some are clicky. I am guessing that all of them ware supposed to be clicky but the springs got bent enough with use that they don't provide the buckling action anymore. But i prefer the soft feel of the worn out ones. I was guessing if jabbing the spring with a Flathead screwdriver would bend it enough to "break" the clicky action of the switch.

Berni, actually the 'soft' ones are those that are working properly.  They're the bog-standard leaf spring switches that HP used in skazillions of instruments back in the day.  The leaf spring is supposed to have a slight curve in it that lets it bend smoothly, but in older instruments they get sticky and don't want to bend properly, resulting in the feeling you describe.

Below is a link to a YouTube video posted years ago by a guy showing how to remove and reform the springs.  I've recently read that the issue can be caused by old lubricant gumming up and preventing the springs from moving properly, and that it can be fixed by flushing the switches with alcohol to clean out the grease rather than taking them apart as shown in the video.

I've flushed a few of them with denatured alcohol and been successful in getting them working again, though some were stubborn and ultimately needed to come apart.

I'd try an alcohol flush first (you may need to hit them two or three times) before going to the trouble of pulling the springs.  Easy stuff first, right?

Here is the video link:
http://www.rbarrios.com/projects/HPSWITCH/

Good luck with it.

-Pat

[Berni]

Oh thanks! I will give that a try.

Not only does my HP 4145 have this problem but also my HP 8566B, all use the same switches. I have expected them to be harder do disassemble but yeah will definetly try cleaning them first since doing this on every single switch could take a while.

[sixtimesseven]

I am just in the process of repairing one of those exact CRT modules in my HP 4145B since the NewScope5 is a bit pricy

It uses the same switches on the front panel and mine also have an inconsistent feeling. Some are soft and some are clicky. I am guessing that all of them ware supposed to be clicky but the springs got bent enough with use that they don't provide the buckling action anymore. But i prefer the soft feel of the worn out ones. I was guessing if jabbing the spring with a Flathead screwdriver would bend it enough to "break" the clicky action of the switch.

Berni, actually the 'soft' ones are those that are working properly.  They're the bog-standard leaf spring switches that HP used in skazillions of instruments back in the day.  The leaf spring is supposed to have a slight curve in it that lets it bend smoothly, but in older instruments they get sticky and don't want to bend properly, resulting in the feeling you describe.

Below is a link to a YouTube video posted years ago by a guy showing how to remove and reform the springs.  I've recently read that the issue can be caused by old lubricant gumming up and preventing the springs from moving properly, and that it can be fixed by flushing the switches with alcohol to clean out the grease rather than taking them apart as shown in the video.

I've flushed a few of them with denatured alcohol and been successful in getting them working again, though some were stubborn and ultimately needed to come apart.

I'd try an alcohol flush first (you may need to hit them two or three times) before going to the trouble of pulling the springs.  Easy stuff first, right?

Here is the video link:
http://www.rbarrios.com/projects/HPSWITCH/

Good luck with it.

-Pat

Nice link. How did he get the key of the switch (I mean the actuall boutton on top of the switch)? I tried to remove the keys since they have yellowed and I tought I could try the Peroxid/UV trick on them... But I didnt manage to remove them.

I had really sticky switches and all I did was spray them with WD-40 contact cleaner spray and they work perfectly now.

[precaud]

Did you build some AC coupled adaptors? Like you, I would prefer not to test my luck! Addressing this now could save any 3577A owner a lot of trouble.

Yes, I had a couple old Tek input capacitance normalizers which I repurposed. I used 100nF caps, which give -3dB @ 3.18Hz. There's probably room for 220nF's in there if I find that cutoff is too high. But I doubt that will be the case. If I need to examine xfer functions below 10Hz, an FFT-based DSA is a much better tool, anyway. Sweepers take forever at such low freqs.

: No built-in power splitter. A silly omission.

Is it worth buying a commercial splitter for under 200Mhz or is it easy enough to DIY? Searching around for some info - they only seem difficult when the BW goes much beyond 500Mhz.

Probably not worth buying. I made mine, using closely-matched 1/2W axial MF resistors I had on hand. It's good beyond the 30MHz upper limit of the Anritsu VNA I mostly use. I've never used it with the 3577A. And given Berni's excellent results with 0402's, making one is a no-brainer.

For power supply/PDN stuff you probably won't be working above 10MHz, anyway. When you do, come back and tell us about it! 

[Cubdriver]

I used one of those crook-necked lab squeeze bottles to flush the springs with alcohol - it lets you direct the flow and get some force behind it so it gets into the area under the spring.  Actuating the switch as you squirt it seemed to help, too.

Ideally you'd gently (so as not to dislodge the springs) blow them out afterwards with compressed air, but my compressor was down when I did the ones on my 8662A so I just let them air dry.

-Pat

[Cubdriver]

The key caps should just pull straight off the switches.

-Pat

[rx8pilot]

For power supply/PDN stuff you probably won't be working above 10MHz, anyway. When you do, come back and tell us about it! 

Exactly - 10Mhz will be a typical cutoff for those efforts.

I have some Samtec SMA's that I can use to solder a splitter together rather quickly. I feel like this learning curve will visually reveal characteristics of components and circuits that are otherwise rather mysterious and hard to understand. Somehow.....this is fun even though it is technically for work. As it is said.....'love what you do and never work another day in your life'

[precaud]

Exactly - 10Mhz will be a typical cutoff for those efforts.

I have some Samtec SMA's that I can use to solder a splitter together rather quickly. I feel like this learning curve will visually reveal characteristics of components and circuits that are otherwise rather mysterious and hard to understand. Somehow.....this is fun even though it is technically for work. As it is said.....'love what you do and never work another day in your life'

Totally agree on all points!   

[bson]

May I ask which active probes you use exactly?

I have a ZS1000, AP020, a differential AP034, and an AP022.  They see use in roughly that order...  With the powered BNC adapter, mainly the AP020 or AP022.  (The AP022 isn't recommended for use with the ADPPS, due to lack of offset zeroing, but it seems to zero just fine for me... But I wouldn't get it for that purpose.)

[sixtimesseven]

Does anyone know which style of panel N-Connector HP used for the 35677-63504 / 35677-63502 "Directional Bridge Assemblies" (75/50Ohm) and if somthing similar is still available?

[sixtimesseven]

Today my replacement fan arrived. I could not get the Delta AFB1224HE anywhere so I went for the Sanyo 9WP1224H1011 which was in stock at farnell uk, specs:

99CFM / 0.283in
2600RPM
39dB

datasheet: https://www.mouser.ch/datasheet/2/471/San_Ace_120WP38_E-1286779.pdf

The fan is quiete. Hard to say if it is 10x quieter but it is an improvment. At the 27.5V from the HP3577 the temperatures from the termal camera seem to be about identical to the Muffin fan, at least if I measure at the heatsink of the power supply transistor which is just visible trough the left perforated side (about 51degC).

I do some further testing trying to reduce the fan voltage & noise. Also I will install some vibration dampeners for the fan since I hear some vibrations at the back panel.

[bson]

I'll experiment as well.  Ordered a relatively inexpensive fan and dampeners:

https://www.digikey.com/product-detail/en/G1238L24B1-FSR-EM/1570-1785-ND/8120198/?itemSeq=268069836
https://www.digikey.com/product-detail/en/LZ550/381-2709-ND/5043883/?itemSeq=268069888

[sixtimesseven]

I'll experiment as well.  Ordered a relatively inexpensive fan and dampeners:

https://www.digikey.com/product-detail/en/G1238L24B1-FSR-EM/1570-1785-ND/8120198/?itemSeq=268069836
https://www.digikey.com/product-detail/en/LZ550/381-2709-ND/5043883/?itemSeq=268069888

Good choice! I looked at that fan as well. However, my Digik. list was almost empty and tax&handling is very expensive for me so the Sanyo from farnell was about as expensive all included 
I look forward to your findings!

Also, how will you attach the filter at the back with those rubber attachments you selected? Do you just pull them trough the hole stack? Please report back if they are strong enough to hold everyting together.

[bson]

No idea how things will go together.  I'll see when it comes here, but I have an assortment of long M4 screws, nuts, spacers, O-rings, etc, so even if the fasteners don't work I'll see what I can figure out.   I can also mill a bracket from acrylic if needed.

[sixtimesseven]

No idea how things will go together.  I'll see when it comes here, but I have an assortment of long M4 screws, nuts, spacers, O-rings, etc, so even if the fasteners don't work I'll see what I can figure out.   I can also mill a bracket from acrylic if needed.

Nice!

The hottest part I could find so far was R103 on the power board. At 28 ambient I get about 110-115degC with the original fan @28degC ambient and about the same for the Sanyo with 28V.

[precaud]

I think it would be better to measure the temperature on one of the pcb's in the card nest that runs warm. That's where the effects of fan pressure changes would be greatest, and most consequential. Exposed power components near the fan aren't going to be affected much by it.

[sixtimesseven]

50dBa ! That's one noisey fan! The fan noise and crt are what keeps the 3577A (and 3562A) off my bench. Lovely instruments crippled with noisey fans and hard-to-read crts.

I probably just install a quiet 12V PC fan with a 24V converter and test with the thermal cam if the 80 CFM are enough without the CRT heating the instrument.

The Achilles heel of the 3577A appears to center around the input relays. That was the major design change between A and B versions, a redesigned front end using different relays.

Do you already have some with that issue? I'm still waiting on Artek to get me the service manual so I have no idea yet what these relays are, but are they replacable at all?

Teledyne 412 series apear to be still available at mouser: https://www.mouser.ch/Teledyne-Relays/Electromechanical/Relays/High-Frequency-RF-Relays/412-Series/_/N-5g33?P=1yzsh13Z1z0zl30

Rather expensive if you have to replace all of them! 

IDK, but maybe you can find the HP part number for the relay 0490-1404 in the service manuals of other instruments?

[precaud]

IDK, but maybe you can find the HP part number for the relay 0490-1404 in the service manuals of other instruments?

Yeah, these things are pricey, that alone would have been good reason for HP to move away from them.

I've found a couple other HP instruments from that era that use the same type relay, but not the exact same model. I found a couple 432-series in a DSO (forgot to write down the model number). And the 16531A digitizer plugin for 16500A logic analyzers has a couple of 'em, but I haven't pulled them yet to see their model number. Should be able to pick up those boards for cheap, noone is using them anymore.

EDIT : The 432-series relays came from an HP 54200A, a 50MHz, 200Msa/S 6-bit DSO. The main board has three of 'em.

[sixtimesseven]

IDK, but maybe you can find the HP part number for the relay 0490-1404 in the service manuals of other instruments?

Yeah, these things are pricey, that alone would have been good reason for HP to move away from them.

I've found a couple other HP instruments from that era that use the same type relay, but not the exact same model. I found a couple 432-series in a DSO (forgot to write down the model number). And the 16531A digitizer plugin for 16500A logic analyzers has a couple of 'em, but I haven't pulled them yet to see their model number. Should be able to pick up those boards for cheap, noone is using them anymore.

EDIT : The 432-series relays came from an HP 54200A, a 50MHz, 200Msa/S 6-bit DSO. The main board has three of 'em.

Does using "old" relays make much sense though? I mean they could be at or near their end of life and it would be a shame to go trough the hole adjustment routine just to switch out relays again...

[precaud]

Does using "old" relays make much sense though?

I don't have a problem with it.

I mean they could be at or near their end of life and it would be a shame to go trough the hole adjustment routine just to switch out relays again...

They could be, but probably are not (near their end of life). They've had a very easy life - the 54200A (and 54201x) 's I have here have been sitting around doin' nothin' for more than 15 years. Ditto for the digitizer plugins.

Plus, I tested the instruments before parting them out and the relays were fine.

[precaud]

I'll experiment as well.  Ordered a relatively inexpensive fan and dampeners:

https://www.digikey.com/product-detail/en/G1238L24B1-FSR-EM/1570-1785-ND/8120198/?itemSeq=268069836
https://www.digikey.com/product-detail/en/LZ550/381-2709-ND/5043883/?itemSeq=268069888

Any progress on your fan replacement?

[bson]

I'll experiment as well.  Ordered a relatively inexpensive fan and dampeners:

https://www.digikey.com/product-detail/en/G1238L24B1-FSR-EM/1570-1785-ND/8120198/?itemSeq=268069836
https://www.digikey.com/product-detail/en/LZ550/381-2709-ND/5043883/?itemSeq=268069888

Any progress on your fan replacement?

I have the fan but haven't taken the time to remove the instrument from where it sits to open it up yet...  Given its size and weight that's a 2 person job. :/

[Berni]

And i have fixed the clicky snagging switches on mine with a quicker fix:
https://www.eevblog.com/forum/testgear/hp-4145b-semiconductor-analyzer-repair-with-photos-(display-garbage-dead-rom)/msg1743731/#msg1743731

They all work perfectly now

[precaud]

Any update from folks who have replaced the 3577A fan with a quieter one?

[Berni]

These fans often tend to be pretty high performance fans with a ton of airflow. So most equivalent fans that move the same amount of air are not going to be significantly quieter.

But in a lot of cases these fans are overkill in the first place. They are designed to keep the thing cool when its stuffed snugly into a big rack of equipment that is pumping out heat and perhaps the rack placed into a industrial environment as part of a automated test setup. So what i did instead is slow the fans down by inserting a resistor in series with them, a lot of these fans actually get quite quiet when ran a bit slower, but when doing this i always check the temperature of the hottest components to make sure im not causing anything to overheat by slowing it down too much.

[precaud]

Those are good points, Berni.

I've used series resistance to lower the operating voltage and fan speeds before. But with that approach, pressure would scale down proportional to the speed reduction. Not generally a problem if circulating air in a large, open enclosure. But after looking at the various cooling paths in the 3577, I'm thinking that isn't a good thing in this case. The power supply components probably wouldn't be affected by it; that air path is direct and open. But pressure is needed to push air through the small holes in the bottom of the card nest, and out the holes in the top panel of the cards.

That's why the Sanyo fan looks attractive; it generates the same pressure as the stock fan, with only a little less airflow.

Probably the best move to reduce cooling requirements is to swap the crt out for one of those nice LCD displays. Hard for me to justify that cost though, as long as the crt is still working...

[Berni]

Well the static air pressure can also have a big effect on the noise of a fan too. In my homebuilt x86 NAS project i was trying to cool it all by drawing air trough the small case using a 120mm fan, but no matter what fan i used i could never get it to run near silent while also pushing the required amount of air trough it. Eventually i ended up grabbing a dremmel and cutting out the hole pattern where the fan mounts and blows trough so it was now a wide open hole, this finally solved it and got the noise level down to where i wanted it, now the harddrives are louder than the fan when all of them spin up.

So the restrictive air path could also be one of the things that is making the fan loud, or making turbulent noise as air makes its way trough the restrictions.

Oh and looking at the datasheet for the HP 3577A it claims it uses 450VA max, so that's indeed quite a power hungry instrument, ofrcouse the real power use in watts is likley quite a bit lower, but i think its going to be quite difficult to cool without making a lot of noise. The big ass HP 8566B Spectrum analyzer i have has a power consumption of 650 VA, sounds like a hair drier with the powerful fans and yet still gets pretty hot.

[precaud]

Yes, you may be right. I've had similar experience.

That's why I was asking for feedback from someone who has successfully reduced the noise by replacing the fan.

[bson]

I'm trying to install a NewScope-5 in mine, but can't for the life of me get the CRT out.  The instructions say "on the HP3577A there is one additional screw on the bottom right that needs to be removed" but I have no idea where this screw is.  I've removed every screw that I think can hold it, but it's not budging.  There are two screws on the bottom back, one on the right, one on the left that attach to a captive bracket, but that's two screws and the left one is inaccessible without pulling the assembly partway out.  Just removing the right one won't help.  So I'm at a loss what f*cking screw I need to remove...  I don't care to keep the CRT, it's going in the trash anyway, so at some point I'll just start ripping stuff out from the top until I can disassemble enough to pull the tube out from the front.  But I'd rather not make a mess.  Has anyone else done this already and know where this one additional screw is?

Edit: nvm, it's not at the bottom right but at the top right and looks like it's only holding the top PCB onto the cage.  It's not.  There are also two screws under the right side adhesive cover holding the display by the bezel.  After removing those it slides out.

[precaud]

The crt ass'y slides in on a "shelf". Look down at the bottom of the rear of the crt unit, you'll see one large-ish screw that secures it to the shelf. I bet that's the one.

Did you swap out your fan yet?

[Berni]

I had a quite time getting the same CRT module out of my HP 4145B Semiconductor Analyzer.

That had most of the screws in the silver front bezel, as far as i remember two screws in the front top and two in the front left side (Its those i missed). Some of these are under decorative stickers and some of the identical looking screws found in there actually hold the bezel to other parts, but the ones around the screen hold the CRT module in. Once those are out its just a matter of two or three easily accessible screws in the back, before the whole thing slides out forwards with next to no force. Some screws around the CRT module are not required to be removed because they just hold the CRT module itself together.

But perhaps this instrument has extra screws.

[precaud]

Yeah, the 3577A is the only one I've seen that has an extra bracket at the bottom rear of the 1345A for attaching to the "shelf".

EDIT: OK, sounds like you got it...

[bson]

The NewScope-5 is fantastic.  LOVE IT. 

Applied my advanced arts & crafts skills to the foam liner installation:



LCD mounted in bezel:



Power-on smoke test before closing it up.  I had actually forgotten to plug in the main power cable, so good thing I checked...  Also adjusted the focus trimmer to pick a color scheme.  Also had to move the scan direction jumper to get the image right-side up.



Back in use:



I had planned to replace the fan while I had it open, and I did detach the fan, but couldn't get it out without removing the BNC jacks and I didn't want to go there.  It's possible I could have yanked it out with force.

The ONLY thing wrong with the NS5 kit is I didn't get it a long time ago!

[precaud]

Man, that is SO nice... so much easier to read... congrats.   

[sixtimesseven]

I run the fan mentioned in the first post, so far no problems with it. It is still loud but, but before it was unbarable, now it is about on the level of my HP8753D which is acceptable.
We have a sound pressure meter at work, I will try and remember to borrow it to give you some data.

[sixtimesseven]

Yeah so much better than the CRT!

I have to say the Newscope Displays are top notch, very nice blacks. Much better than my 20 Dollar Aliexpress LCD I hacked on to my 8753 ...
But dam the kits are expensive!

[Berni]

Yeah the price of these Newscope displays is the reason i haven't put one of them in  my HP 8566B. They look great, but the price of it is hard to justify when my CRT still works fine.

[precaud]

Just a general note to 3577A owners.

Should you ever want to go through the adjustments procedures and calibrate your unit (especially the input boards), use the procedures given in the 3577B service manual PDF. The adjustments in the 3577A manuals, both printed and PDF, are incomplete and in the wrong order!

This is true of all revisions of the 3577A service manual.

[rx8pilot]

Just a general note to 3577A owners.

Should you ever want to go through the adjustments procedures and calibrate your unit (especially the input boards), use the procedures given in the 3577B service manual PDF. The adjustments in the 3577A manuals, both printed and PDF, are incomplete and in the wrong order!

This is true of all revisions of the 3577A service manual.

This is an awesome addition to this thread. As an owner of an A model - I think this saved me a pile of time. Thanks.

[Calvin]

Hi,

now that my 3577A is working again, I´m looking for an affordable S-Parameter Test Set or an alternative, since the prices + shipping of these sets are higher than what I paid for the VNA   
Just a Q regarding the connectors of the subassemblies in the 35677 S-Parameter Test Sets.
It looks as if the connectors to and from the coaxial relay (33311B) and the directional Bridges (3577-66502) are all of the SMA female type.
The ´Port1´ and ´Port2´ outputs of the two bridges are of N-type but it appears to me that rather they feature SMAs with an SMA-to-N adapter screwed on.
Is that true?
I assume one doesn´t need additional D-Blocks when a (original) 35677 is connected to the VNA? Are those only required for useage of the VNA alone?
As alternative DIY-Setup ... would those cheap chinese/ucrainian 0.1-3000MHz bridges be suitable (with their Ref-otputs terminated into 50R)?

regards
Calvin

btw. found prices in the 1990 HP catalog - 3577A: 25,570$, 35677A: 4,100$ - which would be ~52,000$ and ~8,400$ respectively. What a whopper

[rx8pilot]

btw. found prices in the 1990 HP catalog - 3577A: 25,570$, 35677A: 4,100$ - which would be ~52,000$ and ~8,400$ respectively. What a whopper

Lol! I paid $200 for mine in non-functional condition. Spent about $15 on parts and about 5-6hrs, now it works perfect. Bargain!!!

[miken]

The ´Port1´ and ´Port2´ outputs of the two bridges are of N-type but it appears to me that rather they feature SMAs with an SMA-to-N adapter screwed on.
Is that true?

It's an actual N bulkhead connector, with threading to attach it to the front panel. The back end necks down to a smaller diameter and solders directly to the board.

I assume one doesn´t need additional D-Blocks when a (original) 35677 is connected to the VNA? Are those only required for useage of the VNA alone?
As alternative DIY-Setup ... would those cheap chinese/ucrainian 0.1-3000MHz bridges be suitable (with their Ref-otputs terminated into 50R)?

The bridges have DC blocking capacitors. They are pretty simple inside, caps, resistors, balun. You could probably make your own without too much trouble.

There is a measurement of the cheap bridge here: https://www.eevblog.com/forum/testgear/test-results-for-the-e-bay-rf-bridge-in-an-enclosure/msg1627738/#msg1627738
Though I will say that I measured one once and got worse results at the low end, better at the high end. Not sure if my mistake or if quality varies.

[Calvin]

Hi,

thank You so much.
Yeah, the 35677A circuitry appears simple ... power splitter, 12dB-attenuator, coax relay, two directional couplers, a couple of some semi-rigid cables, and switch logic, besides loads of nude virgin breath  -aka known as used air- in a way tooo large casing. 
Do You happen to know if the coaxial relay connectors are SMAs?
I ordered a pair of 33311Bs and also a pair of the (orginal) Bridges from transverterstore.com (just to be sure that I don´t get some crappy chinese fake something).
It´d be nice if it could be wird solely with SMA cables.

regards
Calvin

[miken]

Yes, I believe the switch is also SMA. I bought a broken 35677A myself. Turns out it had one broken semi-rigid, typical solder joint break. One bridge measured really bad, so I replaced all the caps with SMD, but it turns out it was just the adjustment screw in the bottom... My future project is to build a VNA inside the 35677A box, plenty of space as you say 

[precaud]

I finally replaced the fan in my 3577A. I found a couple of these in one of my parts boxes and put one in:

https://www.mouser.com/ProductDetail/ebm-papst/W2G107-AD03-13?qs=RViDcLGODe0xrlbxBmPSjg%3D%3D

Result: Noise level reduced by half or more, down to a bearable level. Very worthwhile. And no noticeable drop in airflow. In fact, it feels stronger to me.

The original fan is noisy even unmounted.

[Fretec]

Same fans can be found on Ebay for a good price: https://www.ebay.com/itm/303227534315 (not affiliated or something)

[precaud]

Nice price, until I saw the shipping cost. Another eBay seller WAY overcharging to ship...