Repair: HP 8753C Network Analyzer - Page 1
Forum section: electronics / repair

author: hendorog
author_rank: Super Contributor
timestamp: July 08, 2016, 12:05:33 pm
content: The 8753C VNA I mentioned in TiN's repair thread has arrived today, and thankfully much better packed that his one was.I have been keen to get hold of one of these for quite a while.http://www.ebay.com/itm/HP-Agilent-Network-Analyzer-No-Frame-No-Power-As-Is-/252411867849?nma=true&si=wEiNpJ6q0gpoS313Zzj%252BbBkVaqY%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557Delivery was very rapid, it shipped on Wednesday PM and arrived Friday PM - considering it came from the Philippines to New Zealand via Hong Kong. Shipping large items is quite costly to NZ, thankfully offset by the low price on this unit.The rubber keypad has some missing keys, and the bezel is completely missing. I was worried that there would be some boards missing from inside, but fortunately everything looks to be present. Just lots of dust and dust bunnies everywhere.This was always going to be a repair as the description stated no power and sure enough this was the case when it arrived so off with the covers.There was a red LED showing on the back, which flicked off and on again about once every second. It looks like the power supply is cycling/resetting. According to the manual that LED should be off, and the green one below should be on.I spent some time pulling boards and connectors trying to figure out if the fault was in the PSU (A15 pre-regulator) or in the boards connected to it. In the end I removed the A15 unit as it was still faulting with nothing connected.Inside the A15 unit I checked the caps and discovered a short to ground. After lifting a few components which turned out to be fine, I managed to track that to a bad 60V/5A rectifier diode in -8V rail of the A15 pre-regulator. The short was via the transformer winding.When the diodes were removed it was shorted in both directions, there was also a faint scorch mark on the PCB - CR6 and CR7 just left of the inductor (which looks like a transformer) in the middle of the picI'm going to replace the pair of those with these:http://www.diodes.com/_files/datasheets/ds28009.pdfas I can get them locally from Jaycar tomorrow.Of course I have no idea if that is the only fault, so we shall see what happens tomorrow.To be continued...Service manual for 8753A:www.hparchive.com/Manuals/HP-8753A-Manual-Service.pdfService guid for 8753C:http://www.siliconinvestigations.com/hprep/hp8752/08752-90136-C-serv.pdf

author: TiN
author_rank: Super Contributor
timestamp: July 08, 2016, 02:25:27 pm
content: Yey, sister thread FTW! ebay listing shows me 375$ only for shipping, so it's more than was paid for piece of wreck on my table. Something tells me you will get yours fixed and working much faster than I doI'd appreciate detailed photographs of all boards, if you plan disassembly and cleaning. Got mine disassembled tonight, it was fairly easy except few levers broke. Frame, shield cages and backplane PCB with connectors are riveted together though, so that's as much as you can go without special tools to install new rivets.I'm wondering how hard could it be to upgrade 8753A to C-version, as they share same service manual and most of boards are seem to be same. I know source on C is 6GHz capable (opt.006) and receivers + different brains.Good luck with repairs, looking forward for your success..

author: hendorog
author_rank: Super Contributor
timestamp: July 08, 2016, 07:44:34 pm
content: Yes the shipping was a bitter pill, nearly twice the cost of the unit... I had some nightmares on that thinking I might have paid a fortune to ship a box of broken boards...I'll take pics of the boards today, I have had them all out but not cleaned yet. Any tips on the best method of cleaning them?I hope your confidence isn't misplaced, you have a lot more experience at these repairs than I do. At least the boards don't appear to have been worked on before so there is a chance there is just one fault.My feeling is that upgrading is doable. Note that as I understand it the source in the B and C is not 6GHz capable, but the receivers are. The option 006 still leaves them with a 3GHz source. They get the 6GHz from the 85047 test set which contains a switched frequency doubler.So that is good for you as the A model source won't need to be changed.Thanks and all the best on your repair too!

author: veedub565
author_rank: Frequent Contributor
timestamp: July 08, 2016, 07:58:51 pm
content: Looks nice, we still use those a lot at work. Keep us posted

author: TheSteve
author_rank: Unknown
timestamp: July 08, 2016, 08:34:27 pm
content: What do you intend to use it for? The 4 port models often go for less then the 2 port/s parameter units. I've only bought 2 port units as I'm most interested easy s parameters. Or will you be adding a test set?Either way good luck with the repair - hopefully a simple power supply fault.

author: hendorog
author_rank: Super Contributor
timestamp: July 08, 2016, 09:48:35 pm
content: Quote from: TheSteve on July 08, 2016, 08:34:27 pmThats a good question, but hard to answer - I need to practise my response as pretty soon SWMBO will be asking the same question.There are a few reasons.Mainly it is probably for learning, and just to see where it leads. Learning about this stuff is so much easier when you can see the results live on the screen.I've been making my own VNA for up to 6GHz as there was nothing affordable available. I want to be able to compare what that says with this. Also since I have never used a real one I wasn't sure how the UI should work.The GHz frequency VNA motivation originally came from testing my home made antenna's for FPV model aircraft at 5.8GHz. However since then I've learned more and have more ideas of things to use it for. Building LNA's, phased antennas, filters, SDR etc, etc.The other consideration is financial - If I ever have to sell it I should be able to get my money back as these are rare in NZ but still desired.Quote from: TheSteve on July 08, 2016, 08:34:27 pmYes that is what I have found too - the 2 port units are very nice but very hard to get hold of cheap. The downside is that the 006 option is more than just a software key, and the ports are not available externally (I think thats another option) so bodging something using RF parts is more difficult.The other consideration for me is the freight cost - the 2 port units are larger and heavier. I did work out that I could possibly just squeeze a 4 port unit with the test set packaged separately into the limits of the NZ Post cheap freight forwarding service. The 2 port units are too big for that. That was the plan until this one came up anyway.I want to get a test set. Ideally I'd like the 85047A with built in doubler to 6GHz, but those go for crazy money. So I'm thinking I will get a T/R set for up to 3GHz and bodge up something with a Hittite doubler, splitter and a directional coupler for the rest of the range.I have some HP coaxial switches that I could use.Quote from: TheSteve on July 08, 2016, 08:34:27 pmThanks, I hope so too.

author: hendorog
author_rank: Super Contributor
timestamp: July 08, 2016, 09:50:02 pm
content: Quote from: veedub565 on July 08, 2016, 07:58:51 pmThanks, I might need to ask you guys who have these already how to use it if/when its working

author: TheSteve
author_rank: Unknown
timestamp: July 08, 2016, 10:46:17 pm
content: I've bought an 8714C and 8711B, both had issues related to the power supply. The RF portions of HP network analyzers are impressively reliable. There is still an 8711B sitting on ebay I know of that should only have a power supply fault(only good to 1.3 GHz though).I have assembled some 5.8 GHz antennas as well and am still looking for a deal on a cheap/broken 6 GHz VNA. I really only look for ones with power supply or display type faults. For now I use a 6 GHz spectrum analyzer that has a builtin return loss bridge - so I can at least see if they are "tuned".

author: hendorog
author_rank: Super Contributor
timestamp: July 09, 2016, 07:01:21 am
content: Quote from: TheSteve on July 08, 2016, 10:46:17 pmThey look very nice. You could make a transverter to extend the frequency range perhaps?I've also been using the SA approach too with the Signalhound SA+TG. Actually I might not have taken the plunge on the VNA if I didn't have an SA in case I needed it for troubleshooting.

author: hendorog
author_rank: Super Contributor
timestamp: July 10, 2016, 09:57:23 am
content: Well there was a twist in the tail of this repair.Sorry this is a bit of a ramble, I had intentions of posting updates regularly but it was a fight against time to get as far as I could before the end of the weekend.Well I replaced both of the diodes in the -8v rectifier in A15 - and it fired up happy as larry with just the post regulator and cpu boards in. The A15 PSU red LED went off and the green one was on which is good. The A8 postreg board was showing all but one green LED lit for the power rails. The LED which was off was just the front panel power for external probe/bias, and had a blown fuse, so I could ignore that for now.So looking good and I started adding boards the back in again.Unfortunately when I nearly had all of the boards back in, the A15 pre regulator reset and then blew one of the new diodes.Tried again and I got it to the point where it would run, but as soon as I added more boards it would die. Blew another couple of diodes trying to figure out which board was faulty. Lucky I brought 10 of them...I started using a multimeter with a temperature probe to keep an eye on the replaced diodes, and was able to nurse it for long enough to see the screen was good and the front panel was working - apart from the missing buttons of course and glitches caused by the missing boards.I started looking for what was causing the problem assuming that something was overloading that rail, but couldn't get anywhere. The problem rail was -5.2V, and was used in several boards. The confusing thing was that the rail was fused on the A8 post reg board, and that fuse did not blow. So either the problem was prior to the fuse, or there was still an issue in the A15 PSU which feeds it with -8v. I don't have board extenders so there wasn't much I could probe with the boards in place.Several dead ends later I was still confused by one thing. The -5.2v rail was fused for 4A and the fuse wasn't blowing - so perhaps there really was nothing else wrong. I thought I better find out what the current actually was. Easy enough to do by desoldering the -8v line from A15 to A8. And sure enough it was only drawing 1.6A with all of the boards installed.The 6A1 diodes were overrated in both voltage and current - 100V vs 60v and 6A vs 5A and were physically much larger so they must be better - yeah right. I even tried using two in parallel, but that didn't help.One of the original diodes was still working, I'd removed it along with the dead one. I measured it and noticed that its forward voltage read quite a bit lower than the new ones.... Maybe HP had used some flash harry diodes and my replacements were not up to the task? So google got a bit of a thrashing and I schooled up on how to choose diodes in a bridge rectifier.This page was helpfulhttp://electronics.stackexchange.com/questions/48688/selecting-the-right-bridge-rectifierThe part number was readable so I found the datasheet of the original part  - (doh, should have done that sooner, instead I was working from the schematic for the older 8753A/B and I couldn't find those part numbers on the web):https://www.fairchildsemi.com/datasheets/SB/SB560.pdfHere is the replacement I used http://www.diodes.com/_files/datasheets/ds28009.pdfVf = 0.67 vs 0.9Thermal resistance = 25degC/W vs about 10-20degC/W depending upon lead length.Then I saw that the thermal resistance of the new diode seems to require a ground plane of 25mm^2. This board didn't have that, so maybe the diode just couldn't dump enough heat out the leads into the PCB? And the physical package being rather large (9mm diameter) maybe not be as efficient at dissipating heat into the air.The other difference was the original diodes were Schottky. I don't know if that makes any other difference in power dissipation apart from the lower forward voltage?So off I went to the old mates at Jaycar again and came back with pretty much every Schottky diode they had over 3A.First cab of the rank was MBR735 - 35V 7.5Ahttps://www.fairchildsemi.com/datasheets/MB/MBR735.pdfAaaand we have a winner.I plugged all of the RF cables back in and it has been solid ever since.Well apart from one loud bang complete with smoke from the CRT enclosure.The CRT - which is colour and quite dim - turned bright green.I quickly turned it off, thinking that was good while it lasted....Crossed my fingers and turned it back on and happy days it still works. I expect was due to dust on the tube.I've been able to test the source and it looks OK - unlocked as I need to feed the R input to lock it and I've only got one N-SMA adapter.Here area some board screenshots TiN, sorry just using a phone camera and I haven't yet taken the RF shields off.I will try and do better ones, and I will do the RF modules as I need to clean them anyway - they are full of dust.

author: TerraHertz
author_rank: Super Contributor
timestamp: July 10, 2016, 11:04:26 am
content: Quote from: hendorog on July 10, 2016, 09:57:23 amIt does make a difference, most importantly in this instance because the lower Vf results in lower dissipation at the same current. This is probably why the first diodes you tried were failing.In switchmode supplies there are other important parameters too, such as turn-on and turn-off times, and stored charge - all of which can cause excessive thermal dissipation at high switching frequencies.

author: hendorog
author_rank: Super Contributor
timestamp: July 10, 2016, 11:26:53 am
content: Quote from: TerraHertz on July 10, 2016, 11:04:26 amThanks - I've got a bit of learning to do on switching supplies. I really fell for the numbers on the original diodes.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 10, 2016, 11:48:28 am
content: Turn on time of the diodes is usually not a problem unless you use high voltage PIN diodes and really fast slopes. Even a "slow" diode like the 6A1 or an 1N4001 will be rather fast on turn on - mainly limited by lead inductance.The turn off time can be important. The stored charge is just a different way to express the same property.Chances are the lower V_f solved the problem. Power ratings on a tightly packed board can be tricky - this is especially bad with SMT parts.

author: hendorog
author_rank: Super Contributor
timestamp: July 10, 2016, 08:51:30 pm
content: Quote from: TerraHertz on July 10, 2016, 11:04:26 amQuote from: Kleinstein on July 10, 2016, 11:48:28 amHmm.Even at the quoted worst case Vf of 0.9v and 1.6A the 6A1 diode only had to dissipate around 1.5W.According to the datasheet the worst case is 20degC/W so only 30 degC temperature rise above ambient.They were at least 5 times hotter than that even when the current was reduced, so I'm pretty sure Vf isn't the primary driver.So there must be some other factor at play. Either turn off time, or the 6A1 simply cannot operate without a ground plane to dump heat into.

author: orin
author_rank: Frequent Contributor
timestamp: July 10, 2016, 10:35:47 pm
content: Quote from: hendorog on July 10, 2016, 08:51:30 pmIt's switching loss in the diode. See the first part of this:http://www.allaboutcircuits.com/technical-articles/switching-losses-effects-on-semiconductors/The loss is usually negligible in a linear supply at 50/60 Hz, but the switching supply in the 8753C runs at 60kHz, so the switching losses are 1000 times greater since you get the loss every time the diode switches off. Switching losses in Schottky diodes are much less, hence their use in switching supplies.Has Dave done a video on switching losses yet?

author: hendorog
author_rank: Super Contributor
timestamp: July 11, 2016, 12:03:22 am
content: Quote from: orin on July 10, 2016, 10:35:47 pmThanks that makes perfect sense now. It was quite amazing how cool the new diodes run.In light of that I will try some other Schottky's with the same axial package as the original. The current ones work well but are not physically robust in that spot.

author: hendorog
author_rank: Super Contributor
timestamp: July 12, 2016, 12:22:49 am
content: Some more progress. I installed these axial diodes instead of the TO220 ones.Pulled the A3 source unit out and gave it a quick dusting. Got some photos of the board part numbers, but I didn't disassemble completely.New keypad rubber arrived this morning, installed and that makes it much more pleasant to use - no need for a bent paper clip to press buttons anymore!I joined the HP Agilent equipment group on yahoo, and quickly found that is a goldmine of information about these units.Some interesting finds:* Software options can be enabled by removing an eeprom and modifying the correct locationshttp://www.ko4bb.com/doku2015/doku.php?id=test_equipment:restore_eeprom_of_hp_8753* Options can be enabled by emailing the right guy with your serial and model # [email sent, will see if this is still the case]* External monitor can be connected via one of these [easy but expensive option]:http://www.aliexpress.com/item/Industrial-video-converter-GBS8219-XVGA-BOX-CGA-EGA-MDA-RGB-RGBSOG-RGBSync-RGBHV-TO-VGA-CONVERTER/32631766393.html?spm=2114.01010208.3.9.3Gcsw0&ws_ab_test=searchweb201556_8,searchweb201602_2_10037_10017_405_404_407_406_10032_10040,searchweb201603_8&btsid=3114812f-5851-4da5-b29d-b9ec26c469b4or, [this requires simple hardware mod but is cheaper]https://groups.yahoo.com/neo/groups/hp_agilent_equipment/conversations/messages/73654http://www.aliexpress.com/item/Games-video-converter-CGA-EGA-YUV-TO-VGA-signal-2VGA-OUTPUT-GBS8220/541420074.html?spm=2114.01010208.3.1.SLP6F7&ws_ab_test=searchweb201556_8,searchweb201602_2_10037_10017_405_404_407_10033_406_10032_10040,searchweb201603_8&btsid=b558e5e2-ad7d-4f95-a22a-f1240243664bPost keyboard replacement:

author: hendorog
author_rank: Super Contributor
timestamp: July 16, 2016, 12:38:26 am
content: A few updates:I've made a new front panel using the 3d printer, this makes the rubber soft keys much easier to use.This is used in place of both the bezel/glass part and the menu button cover which were missing.I've found some genuine parts which are on the way.Software options are installed and working for 002 (Harmonic analysis), 006 (6GHz), and 010 (Time domain) - thanks to a top bloke on the HP Agilent group.Have purchased this 85044A T/R Test set for $200 which was a great price. (There was an even cheaper one which looked a bit scruffy, but they ignored my messages about shipping and ignored my offers so I thought stuff them)http://www.ebay.com/itm/222084316012?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITand this 7mm to SMA adapter:http://www.ebay.com/itm/7mm-to-SMA-f-Adaptor-OMNI-SPECTRA-OSM-2082-2700-00-/172255016882?hash=item281b32f7b2:g:3UAAAOSwiYFXHyXlOn the electronic front I've discovered one of the tests is failing: Test 17 - ADC Linearity. The instrument seems to be measuring normally so any error this is causing is reasonably subtle. Noticing that the test passes when run straight after power on from cold, I also got it to pass the test when warm by pulling the A10 ADC board, cooling it (gently) with freezer spray and then reinserting, powering up and testing before it got warm.Tried to narrow it down by only cooling only one half of the board, but had a wee hiccup when the PSU suddenly shutdown. Fortunately it came back up after a few minutes, probably I overdid it on the cooling spray and caused some condensation. I've got another board on the way as a backup before I try again...

author: TurboTom
author_rank: Super Contributor
timestamp: July 17, 2016, 12:14:59 pm
content: Hey, well done repair job, congrats on that! On my 8753C, I had an analog multiplexer (U8) on the A10 digital IF board fail. It was quite difficult to spot since the instrument initially only reported the well-known "No IF found..." message as if there wasn't any RF fed back to the reference input. Funnily, the message disappeared in the upper frequency regions if a reference signal was fed back. But still the analog bus readings were all over the place. Fortunately, there are many test points at the top edge of the PCBs so step by step I could narrow the problem down. The schematic available on the web (for the 8753B) fortunately is similar enough to be of considerable help.I replaced the HI1-518-5 multiplexer with its "commercial" counterpart HI3-518-5 since an original spare wasn't available. The instrument performs well after the rapair and all readings are correct again (as far as I can tell). It seems the multiplexers are somewhat prone to degradation/failure so yo may check yours as well.Good luck and all the best,Thomas

author: dr.diesel
author_rank: Super Contributor
timestamp: July 17, 2016, 12:21:34 pm
content: WooHoo, I just bought one of these busted on eBay as well. Anxiously awaiting for it to arrive.

author: TiN
author_rank: Super Contributor
timestamp: July 17, 2016, 12:24:25 pm
content: VNA spree beware.hendorogAre you considering to get LCD kit for your box?

author: hendorog
author_rank: Super Contributor
timestamp: July 17, 2016, 08:00:16 pm
content: Quote from: TurboTom on July 17, 2016, 12:14:59 pmGolden info on the multiplexers, thanks! I was looking at the items in the signal path wondering what the most likely culprit could be.That gives me somewhere to start as tracing a linearity fault through the board didn't sound like much fun

author: Vgkid
author_rank: Super Contributor
timestamp: July 17, 2016, 08:08:58 pm
content: Nice job on the new front display.

author: hendorog
author_rank: Super Contributor
timestamp: July 17, 2016, 08:24:16 pm
content: Quote from: dr.diesel on July 17, 2016, 12:21:34 pmNice one! Looking forward to hearing more about the repair.Which one did you get?Quote from: TiN on July 17, 2016, 12:24:25 pmI thought about it but decided probably not - I've run the CRT adjustments and got it to the point where its OK to use in daylight and perfectly fine in the evening.The LCD kits didn't seem to be marked as compatible with the C model either. Other seem to have installed them though so probably not an issue there.I'm considering getting one of the cheap modules mentioned above to plug in an external monitor - which would be easier on the eyes than the small LCD.How are you guys getting on with your one?

author: hendorog
author_rank: Super Contributor
timestamp: July 17, 2016, 08:28:53 pm
content: Quote from: Vgkid on July 17, 2016, 08:08:58 pmThanks - forgot to mention I posted the files on thingiverse in case anyone needs it.http://www.thingiverse.com/thing:1675565

author: hendorog
author_rank: Super Contributor
timestamp: July 19, 2016, 11:28:49 am
content: I've been messing around with the correction adjustments trying to clean up the spurs on the source. It had a lot of spurs, the main ones are multiples of 25.5kHz.To do this I needed to adjust the trimpots along the top edge of the A13 Frac-N board. The adjustment is called "Fractional-N Spur Avoidance and FM Sideband Adjustment" in the Service manual. It's an automated test and requires a heap of HP gear none of which I have.So instead of that I just cautiously tweaked one of the pots in CW mode with a SA connected, and watched to see what would happen. When I saw the spurs dropping I carried on and did the others.I also did the Source Spur Avoidance Tracking adjustment, which is simple. Just monitor a trace on the VNA itself while tweaking the obvious pot on the A3 source. Need to connect a test point and GND to the Analog bus using jumper leads. This wasn't that far out of adjustment and I don't think that made any real difference to the source trace that I could see.And the Cavity Oscillator Frequency Correction Constants, which is used to correct the frequency of the Cavity Oscillator for aging. It involves identifying a particular spur of the oscillator on the screen. This is pretty difficult unless you have an appropriate filter. I don't so intend to make one and repeat this adjustment.Forgot to save before pix which was dumb. Unfortunately I wasn't able to reduce the 25kHz spurs, but there were other spurs which have pretty much dropped into the noise.It would be good to know if this is a typical source compared to other 8753 owners. I did find an old post on the Keysight forums of someone observing the 8753A model is typically cleaner than the 8753C model, which often has spurs. There wasn't any info about reducing them however.Edit: Added images showing the source when unlocked (Source Tune mode). Note there is27dB37dB of attenuators in the path in these pics. When looking at it from a wide span (last image) it appears normal. The narrow span in realtime mode looks pretty bad and I'm wondering if something is modulating it somehow. There is a regular 'glitch' which shows to the left of the fundamental. Any ideas?

author: TurboTom
author_rank: Super Contributor
timestamp: July 20, 2016, 08:41:03 pm
content: I just checked with my 8753C and found a very similar spur spectrum. I didn't touch any adjustments on mine so I don't know if this can be improved significantly -- but I doubt it. After checking the 1GHz (btw, mine is slightly low so it may be a good idea to use an external reference if something really accurate needs to be done) for the spurs (first and second screenshot), I decided to check for harmonics, first with a generator amplitude of 0dBm (nothing visible above the SA noise) and then with the generator power increased to 20dBm -- surprise, surprise! But I guess that's simply the price to pay when cranking so much power out of the poor hybrid...For what it's worth, my VNA had been calibrated the last time in 2003 and wasn't touched since (I broke the seals).I hope this information may be a little usefulCheers,Thomas

author: hendorog
author_rank: Super Contributor
timestamp: July 20, 2016, 08:50:34 pm
content: Great stuff, thanks Thomas!Any chance you could try it unlocked in Source Tune mode too?If you can, the key combo is:[SERVICE MENU][SERVICE MODES][SRC TUNE]Then look at it with a narrow span and see if it looks anything like mine.Cheers,Roger

author: TurboTom
author_rank: Super Contributor
timestamp: July 21, 2016, 07:13:33 am
content: Roger -certainly it looks similar like yours (or it would if my SA would feature this kind of intensity/color grading of multiple sweeps)Actually, this is no surprise since in this test mode, the YTO is not locked but rather free-running, just controlled by the pretune voltage. Hence it drifts and all the noise in the pretune circuitry (since not compensated by the PLL feedback loop) manifests itself as phase / frequency noise. I think this test is simply meant to check if the pretune circuitry puts the YTO somewhere close to the preselected frequency so the lock time for the PLL would be as small as possible. As long as this is approximately correct, all the jutter and drift aren't really relevant. I might be proven wrong, though...All the best,Thomas

author: hendorog
author_rank: Super Contributor
timestamp: July 21, 2016, 11:49:09 am
content: Thanks Thomas- yours looks more stable than mine, but at least it does look quite similar and so is probably normal.My SA has some nice features and some not so nice ones, but it suits my usage quite wellI do like the look of that new Siglent though.Even without the PLL lock I think it could be more stable than this. I'm just not sure if its done by design or not.I was wondering if the modulation here could be related to the spurs in the PLL locked output.I tried it on zero span on my SA with FM demodulation and that shows a regular pattern which is interesting. The downward pulse visible in the top trace is the 'glitch' which is in the earlier pics with the persistence.

author: hendorog
author_rank: Super Contributor
timestamp: July 23, 2016, 08:33:08 am
content: I finally pulled out the CRT and found a wee surprise.The penny dropped - the bang and the smoke back when it first started up was actually this cap going off.When that happened the CRT was extremely bright until I turned it off. Also it was difficult to get a linear brightness out of the calibration.I can get 47uF or 10uF 250V caps locally but not 22uF. So a choice: Bodge it or wait?Onwards with the bodge then...

author: hendorog
author_rank: Super Contributor
timestamp: July 24, 2016, 08:07:42 am
content: This is pretty cool. I have been wanting to test out the 8753 in 6GHz mode. Even with the 006 option installed the VNA RF source only goes to 3GHz. So to get 6GHz you need an 85047A test set which has a doubler which switches in for 6GHz mode and out for 3GHz mode. These test sets are crazy expensive on eBay, and cost more than what you can get a 8753C for.So I've been working on writing some PSoC code to respond to the VNA like a test set would. Then I can put a basic test set together using cheap doublers and couplers and use the VNA up to 6GHz. I just got the PSoC working, and using a mixer as a makeshift doubler was able to play with 6GHz mode. Although the mixer didn't suppress the fundamental so it was difficult to reliably get it to lock though.Well I discovered that the extra hardware that isn't required, at least for playing around, as there is a POKE which does the same thing.The A9 jumper needs to be in Alter position for this to work according to the doc.The address is: 1314412POKE: 5 for 85047POKE: 1 for 85046POKE: 0 for no test set.Press PRESET afterwards.One of the pics shows a new menu option which appears allowing the choice between 3 and 6GHz sweep modes.It may be possible to set this up as a programmed Sequence, so it can be called up at the press of a button.*** TRAP for young players: Turning on 6GHz mode automatically sets the source power to 20dBm. So don't do this with RF Out connected directly to R or through a splitter without additional attenuation ***I found this in the 8753D service guide: 08753-90406-d-serv.pdf [8753D Option 011 Network Analyzer Service Guide Manual]http://www.siliconinvestigations.com/hprep/hp8753/08753-90406-d-serv.pdfI'll still use the PSoC as I'm planning to make a test set for using up to 6GHz.Analyzer is back in action again, cap in the display replaced with a 10uF 400V for now. Its not the correct value, but I figured less capacitance was the lesser of the two weevils.I also replaced the supercap with a larger 1F one as I thought it was faulty. The display colour resets to default after restarting. Turns out that this still happens so the original was fine. The user settings I had saved were all lost as expected.Lastly there is a pic of measurement of the voltage across the source pins ID- and ID+. This measurement should be within the range printed on the label attached to the source - in my case it is OK as the range is 380mV to 485mV. If this is too high or too low it likely means there is a problem with the source wire bonded microcircuits - hard and/or expensive to fix. So this would be a worthwhile test for someone looking to buy one of these.

author: tautech
author_rank: Super Contributor
timestamp: July 24, 2016, 09:37:45 am
content: Quote from: hendorog on July 23, 2016, 08:33:08 amWhat's all these then?http://nz.rs-online.com/web/c/passive-components/capacitors/aluminium-capacitors/?searchTerm=22uF+250V

author: TiN
author_rank: Super Contributor
timestamp: July 24, 2016, 09:48:37 am
content: Thank you for tips and sharing. It would be also great to see your progress in test set build, if you decide to go thru and worklog that project.

author: hendorog
author_rank: Super Contributor
timestamp: July 24, 2016, 10:17:06 am
content: Quote from: tautech on July 24, 2016, 09:37:45 amHah thanks that will be handy, I didn't even think about them!I do remember knowing about them years ago - I was more into software and automation then but was working with some EE's.

author: tautech
author_rank: Super Contributor
timestamp: July 24, 2016, 10:30:55 am
content: Quote from: hendorog on July 24, 2016, 10:17:06 amBookmark this one too:http://nz.element14.com/

author: hendorog
author_rank: Super Contributor
timestamp: July 24, 2016, 11:46:56 am
content: Quote from: tautech on July 24, 2016, 10:30:55 amYep I knew about them, haven't used them though.

author: hendorog
author_rank: Super Contributor
timestamp: July 24, 2016, 08:57:17 pm
content: Quote from: TiN on July 24, 2016, 09:48:37 amGlad it's of some helpYep I am planning to do that.Here is some info about where I'm at:This doubler PCB and MMIC's are on the way:http://www.ebay.com/itm/Develop-PCB-Hittite-Doubler-HMC188MS8-with-2-MMIICs-/160794801260?hash=item25701df46c:m:mdEwzLLPGZOcXNZKX8dcbxwAnd I scored (gambled on) these cheapish directional couplers with no spec. Given the part numbering, I was hoping these were out of the 3600 20GHz test set for the Wiltron 360 VNA.http://www.ebay.com/itm/262433378082However I've now found a parts manual and it's not the same part. D-20363 is the 20GHz coupler in the 3600 test set, these are on eBay and are not the same.So I'm not sure what these are from and what they will be like. They will still work fine, since some qualities can be compensated by the correct type of VNA calibration, but there will of course be some loss in accuracy.I'll make a resistive splitter for the R Channel, and will also try to make a bridge so the couplers aren't needed. I'm anticipating that the bridge will be the most difficult part of this and so having off the shelf couplers will provide a quicker path to getting it working initially. Will probably ultimately use Peregrine switches, but I've got some HP coax switches to get started with.

author: hendorog
author_rank: Super Contributor
timestamp: July 27, 2016, 01:05:26 am
content: Quick warning about this ebay sale which looks dodge to me.This is being sold as complete but not working -from a new seller with only 3 sales:http://www.ebay.com/itm/Hewlett-Packard-8752-Network-Analyzer-300kHz-3GhZ-/252476809778?&_trksid=p2056016.l4276I'm sure it is the same device as this sale which just ended unsold from a different seller with 127 sales:http://www.ebay.com/itm/HP-Agilent-8752C-Network-Analyzer-50-3GHz-/182183359815?_trksid=p2047675.l2557&ssPageName=STRK%3AMEBIDX%3AIT&nma=true&si=BbDQC%252BFdNe6m7UJDAfxrtrI8rGU%253D&orig_cvip=true&rt=ncThe original sale had a pic of the inside. It is not complete.Major issue is the (expensive) source does not look like the correct one for the 8752 and the interconnecting cables are all missing.Minor issues various parts missing like power button, feet, trim etc.The thing looks like a parts unit and may just be full of broken bits.

author: hendorog
author_rank: Super Contributor
timestamp: July 28, 2016, 09:29:52 am
content: I have isolated the source of the spurs.The clue was something I just read on the Keysight forums - that 25.5kHz was the sync frequency used for the external monitor. Aha, that is also the offset of these spurs from the CW.Initially I thought my routing of the external monitor cables was the issue. Playing with that didn't help.Then I tried disconnecting the CRT and blind keying into CW. Big improvement in all except the 100kHz spur which gets worse for some reason.That spur has its own tuning pot but I couldn't reduce it any further.The key question is does this affect the device? I have noticed some very occasional glitches in the CW signal, which makes me wonder if the spurs are high enough to confuse the phase lock. Apart from that everything seems comfortably better than spec.85044A T/R Test set has arrived. Its ex Colorado Uni and by the look of the dings in it, it has taken some punishment. I'm one 7mm to SMA adapter and one N to SMA shortso can't fully test it. However I tested each channel (R and A) individually and it seems to work OK.Pulled the cover off it - it has little plastic zip slider things, no screws. Opened up the directional bridge and wow, it is a thing of beauty inside. Wish I had a better camera.Top gold box is coupler/bridge, bottom silver box is variable attenuator. Connections on right are - top bias from VNA, middle top A to VNA, middle bott R to VNA, bottom RF from VNAInside the gold box.Old repairRF input comes from the right via the choke, bottom is test port, left goes to reflected A output to VNA, top goes to termination resistor.Tiny Termination resistor at the end of the line from the Test port.13dB Compensation, to cable strangely routed the long way around the front of the case, goes to R outputSplitter - top exits to variable attenuator, botton to fixed 13dB complensationPin coming in on centre right is RF input from variable attenuator. Heads left via the choke to the coupler Resoldered cap visible. Lower right is bias input.Edit: Found a schematic for the 85044A Test Set

author: dr.diesel
author_rank: Super Contributor
timestamp: August 03, 2016, 09:51:03 pm
content: Quote from: hendorog on July 24, 2016, 08:07:42 amThe supercap supports specific test offsets, user preset type of data, not instrument calibration correct?Reading/saving EEPROM data might be my next goal.

author: hendorog
author_rank: Super Contributor
timestamp: August 03, 2016, 10:26:55 pm
content: Quote from: dr.diesel on August 03, 2016, 09:51:03 pmYes, the EEPROM stores all of the instrument cal data - i.e. the results of the alignment tests in the manual. This is what you want to back up, although it doesn't seem to be _that_ difficult to run through the tests to re-create it.The user preset data is definitely saved by the supercap, losing those is no biggie.Some unexpected but less important things are reset after an extended time without power (i.e. after say 5 minutes) even with the supercap in place:* User Calibrations <- I haven't worked out if these are supposed to be saved or not. There is an option to save the cal after you complete one, and PRESET then Recall seems to work. However when I power down and come back the next day and Recall the saved preset again it seems to be gone. Other settings are Recalled. Could be PEBKAC error.* Display colours <- There is a separate save and restore function under the Display button which does work for this.

author: KE5FX
author_rank: Super Contributor
timestamp: August 03, 2016, 10:52:48 pm
content: Quote from: hendorog on August 03, 2016, 10:26:55 pmCalibrations aren't saved on the 8753A-C models, unlike the 8510C. A real forehead-slapper on HP's part. Not sure if they are on the -D/-E models.You can save and restore the complete instrument setup/calibration state witha cheesy Windows app I wrote for that purpose.Requires an NI GPIB adapter.

author: hendorog
author_rank: Super Contributor
timestamp: August 03, 2016, 11:06:12 pm
content: Detailed info here - chapter 10http://literature.cdn.keysight.com/litweb/pdf/08753-90901.pdf?id=807274

author: KE5FX
author_rank: Super Contributor
timestamp: August 03, 2016, 11:27:03 pm
content: Quote from: hendorog on August 03, 2016, 11:06:12 pmThe key part is on page 10-2: "Calibration data and memory traces are stored in volatile memory. While this data will survive an instrument preset, it is lost when line power is turned off."So you end up being able to recall the state after a power cycle, but not the calibration that went with it.

author: hendorog
author_rank: Super Contributor
timestamp: August 04, 2016, 03:13:03 am
content: Quote from: KE5FX on August 03, 2016, 11:27:03 pmThanks. The part that was threw me was that the cal and display settings actually survive a (relatively quick) power cycle.Regarding your GPIB utils, do they specifically require the NI or Prologix GPIB controllers or will they generally work with most 'standard' controllers? The cheapest seem to be the HP copies on eBay at about NZD100.The eye of Sauron has now swung in my direction and is scrutinising how much I spend on this stuff so I need to go as cheap as possible

author: KE5FX
author_rank: Super Contributor
timestamp: August 04, 2016, 07:20:13 pm
content: Quote from: hendorog on August 04, 2016, 03:13:03 amUnfortunately, one does not simply use a Prologix adapter with VNA.EXE. It will "work" but you'll see occasional bus lockups. This is especially true with the GPIB-Ethernet adapter, or when using sweeps with larger point counts (>201). There's a lot of additional advice on that subjecthere.This isn't necessarily Prologix's fault, but it's not clear whose fault it is. Probably mine.Others have had good results with the Agilent 82357B adapters in NI488.2 mode, but I have almost no personal experience with those. My recommendation above all others is the NI GPIB-USB-HS models that have been popular on eBay out of China lately. Unlike the "Agilent"-labeled units, they are either not counterfeits, or they're good enough copies that I can't tell the difference. Those are the only GPIB adapters I use at this point.

author: hendorog
author_rank: Super Contributor
timestamp: August 04, 2016, 07:54:14 pm
content: Quote from: KE5FX on August 04, 2016, 07:20:13 pmGreat info, thanks. I'll start looking for an NI adapter.

author: orin
author_rank: Frequent Contributor
timestamp: August 10, 2016, 09:52:18 pm
content: Quote from: hendorog on July 19, 2016, 11:28:49 amReviving an 8753C that came with a blown "A" sampler here. I replaced the sampler with a used one (<$120 from ebay) and am going through the adjustments.Most likely you can use a Mini Circuits SLP-1200 or NLP-1200 filter for the cavity oscillator adjustment. They are reasonably priced - I just got the SMA version on ebay for about $25 shipped; there is one more available as of the time of this posting. The specified HP filters are also available for not much more.

author: hendorog
author_rank: Super Contributor
timestamp: August 10, 2016, 10:02:53 pm
content: Quote from: orin on August 10, 2016, 09:52:18 pmNice one on the repair - btw if you need a part which is too expensive on eBay, try posting on the Agilent/HP yahoo group, there are people there sitting on piles of parts. Or let me know and I'll send you the contacts of the guys I got parts from.Thanks for the heads up on the filters that is good to know and I'll check them out. I think I got the correct spur, but hard to be sure and I'd like to check.Sometimes it's not worth it as shipping to NZ can be expensive and slow sometimes - and I feel I shouldn't be lazy since I have a great way to test the filter

author: orin
author_rank: Frequent Contributor
timestamp: August 16, 2016, 05:55:00 am
content: Quote from: hendorog on August 10, 2016, 10:02:53 pmMy filter arrived today. I can report it works perfectly for this adjustment. I got two very obvious spurs well above the noise.A note about this adjustment. The sweeps until it finds one of the spurs have > two divisions of noise. Once it finds a spur, it dials back the resolution and the noise is like the pictures in the manual for the case with the filter. I was thinking I had excess noise until it found the first spur....

author: hendorog
author_rank: Super Contributor
timestamp: August 16, 2016, 06:08:43 am
content: ThanksDid you happen to notice if the slope of the noise floor matched the manual? I noticed that mine was in the opposite direction, but wasn't sure if it mattered...

author: orin
author_rank: Frequent Contributor
timestamp: August 16, 2016, 07:02:00 am
content: Quote from: hendorog on August 16, 2016, 06:08:43 amThere was no slope that I noticed; it was like the picture on page 49 of the 90156 manual, except my spur was a little to the left of the one in the manual.

author: orin
author_rank: Frequent Contributor
timestamp: August 18, 2016, 05:24:04 am
content: So, with a nice fixed up 8753x, now you want to save instrument setups, you don't have GPIB and want to get data from the instrument, or more importantly, back up the EEPROM.I just built one of these:http://www.dalton.ax/hpdisk/It is working just fine. I managed to save pretty much the entire instrument state to a LIF image on the SD card, then restore the state the next day and continue where I left off, with the 8753C powered off in between. The latest lifutils (which can be built for Windows/OSX/Linux) dragged the files off the image on the SD card and liftext converted them a regular text file*. After that, I imported the data into Excel and made pretty graphs, but that's beside the point. If you aren't scared of 0603 surface mount and have a PIC programmer, I recommend this project. (I prefer 1206 parts for hand soldering myself.)Orin.*You have to tell the 8753x to save the files in ASCII format and even then, it uses a record based format that needs converting to a regular text file. The files get dumped in CITIFILE format and no, I'd not heard of it either. Fortunately, it's close enough to CSV for Excel to read.

author: KE5FX
author_rank: Super Contributor
timestamp: August 18, 2016, 05:48:44 am
content: Quote from: orin on August 18, 2016, 05:24:04 amGet an NI adapter. Seriously. Trust me on this.

author: orin
author_rank: Frequent Contributor
timestamp: August 18, 2016, 06:36:13 am
content: Quote from: KE5FX on August 18, 2016, 05:48:44 amI have one - a PCI GPIB+, and a Prologix Ethernet adapter, and a likely fake 82357B.But dragging an entire desktop computer to the 8753C or vice-versa would be a pain... Actually, I had some success with the Prologix and VNA.EXE dragging data off the 8753C - but I was asked for s1p files - a future enhancement for VNA.EXE?

author: KE5FX
author_rank: Super Contributor
timestamp: August 18, 2016, 07:35:05 am
content: Quote from: orin on August 18, 2016, 06:36:13 amThat's probably doable. Let me know if you still need it and can test it (I've never had a requirement for .s1ps, myself.).You can always cut out the unwanted 3 columns (well, 6) from an .s2p file, if worst comes to worst.

author: hendorog
author_rank: Super Contributor
timestamp: August 18, 2016, 08:38:12 am
content: Thanks Orin, that is an interesting project, as you say no PC required. I don't have any PIC stuff though.I've been looking for a cheap NI adapter but haven't seen any. Their clones are more expensive than the HP ones...I am tempted to try to make a USB adapter with a PSoC as I have a few dev boards here. There is the PIC example and another Arduino project with source code to base it on.

author: orin
author_rank: Frequent Contributor
timestamp: August 18, 2016, 09:44:14 pm
content: Quote from: KE5FX on August 18, 2016, 07:35:05 amI'll see how Dr Kirkby does with the s2p files I sent him... or whether he still wants s1p.Thanks, Orin.

author: hendorog
author_rank: Super Contributor
timestamp: August 21, 2016, 09:45:50 pm
content: Quote from: orin on August 16, 2016, 05:55:00 amOk I finally got around to making a filter and get the same result - flat noise floor with two very obvious spurs.I think the noise improvement you noticed is just the test auto-scaling the display - which acts to push the noise floor down when the big spurs are on screen.

author: AndersG
author_rank: Contributor
timestamp: August 26, 2016, 01:16:57 pm
content: @KE5FX: "Get an NI adapter. Seriously. Trust me on this"FWIW, my latest firmware for my regular adapter (http://www.dalton.ax/gpib) works with your plotter softwareI am planning an "extended" version of HPDisk, using a processor with more memory where I in addition to emulating a disk, will emulate a printer (to file) and possibly even a plotter. I might steal your 7470 code

author: KE5FX
author_rank: Super Contributor
timestamp: August 26, 2016, 08:24:46 pm
content: Quote from: AndersG on August 26, 2016, 01:16:57 pmDon't steal code from 7470.CPP, steal it from VNA.CPP. Trust me on that, too.7470 is a revolting hack, while VNA is a godsend (at the risk of appearing immodest.)

author: orin
author_rank: Frequent Contributor
timestamp: August 27, 2016, 05:03:59 am
content: Quote from: orin on August 18, 2016, 09:44:14 pmWell, today I was 'playing' with the 85044A T/R test set. I'd set up dual display for S21 and S11 and the 8753C was displaying both after reversing the DUT what seemed like way too many times. I thought I'd use VNA.EXE to grab the .s2p. Not a good idea. The 8753C now wants me to reverse the DUT and hit CONTINUE - which I cannot do as the keypad seems to be locked out. Even if I could have reversed the DUT and hit continue, VNA.EXE would have timed out. Of course, if I had an 85046A or 85047A, it would have been fine.So, I have to see what is doable GPIB-wise... but if there is a way to just grab what's being displayed, that would be much appreciated.Orin.

author: KE5FX
author_rank: Super Contributor
timestamp: August 27, 2016, 09:31:26 am
content: Quote from: orin on August 27, 2016, 05:03:59 amUnfortunately, that's a corner case that VNA has never been tested with. You hardly ever see an 8753 with a T/R test set (or at least I hardly ever have), so it may be awkward to get that configuration working as intended. Unless someone sends me a patch, I probably won't be able to do much about that.

author: AndersG
author_rank: Contributor
timestamp: August 27, 2016, 01:28:57 pm
content: "Don't steal code from 7470.CPP, steal it from VNA.CPP"OKNoted. I am on the planning stage for now. Need to use a PIC with more memory which limits me to 3.3V parts, so I will have to rethink the actual GPIB hardware. Will probably use regular level converter/buffers instead of "real" GPIB chips. Number of pins is no obstacleI can go to a 100-pin PIC if need be, but I should be able to get by with a 44-pin PIC.Will have a peek at your VNA code. I did an ugly hack job in my HP1630 utility that just does printing, but it works, as does your 7470. As ong as the graphs are pretty, who caresEdit: Looked briefly but found no plotter code in VNA.CPP?

author: KE5FX
author_rank: Super Contributor
timestamp: August 27, 2016, 11:53:56 pm
content: Quote from: AndersG on August 27, 2016, 01:28:57 pmIf you set your code up to download .S2P files, you can plot them in any number of good apps from Octave to MATLAB to various freeware and commercial utilities. And if you're writing a disk emulator of some sort, it's better to use the code in VNA.CPP to access the data arrays directly, rather than pretending to be a disk drive.

author: AndersG
author_rank: Contributor
timestamp: August 28, 2016, 12:24:55 pm
content: True. Doing the actual rendering in the emulator might be an overkill. Better just save the streams as is. But the ability to double as a printer/plotter emulator is actually quite asked for. Especially if you have a portable instrument that you drag around and do not want to carry a laptop as well. I have built mine as a small dongle that plugs into the back of my instrument and gets powered from thee.

author: Mrt12
author_rank: Regular Contributor
timestamp: January 25, 2018, 08:14:29 pm
content: Hi guys,I know this thread is not the newest one ;-) but I have a question concerning the 8753C's power supply, and I think it fits quite well into this thread.Well, my 8753C works like a charm, very clean source and good flatness etc. But it has a strange problem. When it is turned on for the first time, no problem at all. If it has run for a couple of minutes and was warmed up and I turn it off and then on again, it doesn't phase lock. Phase lock is only achieved after PRESET in this case.I believe that the problem is related to the temperature of some internal parts, probably the power supply?When the unit is turned on (cold start), I can hear the relays in the test set chattering. However, after a warm start (unit was powered off only for a few minutes), no chattering and no phase lock, but the problem is fixed after pressing PRESET.I am really anxious that the problem may get worse and worse, and will blow some very expensive part some day (e.g. a sampler or even the source, which would be a nightmare!). So, how could I isolate what the problem is? at the moment, I have no idea where I should start. But I suspect the power supply!Because it sometimes displayed the error message 'air flow restricted, check fan filter'. Air flow is monitored by means of three temperature sensors on the post regulator. Checked the sensors, they are fine... and the heat sink is not hot, about hand-warm or a bit more.Any ideas? I try to use my 8753 as seldom and as short as possible to minimise stress, but it's just a PITA when you are nervous every time you turn on the instrument :-)But I really like my NWA. It's probably the most complex instrument I own, and it is also the newest one because I think it's from 1990 ;-) it looks almost brand-new and as I said, works nice except from the power supply thing.Btw, I also updated the firmware from 4.02 to 4.13 :-) see here:https://hb9fsx.ch/wordpress/index.php/2018/01/25/8753c-network-analyser-options/

author: hendorog
author_rank: Super Contributor
timestamp: February 01, 2018, 09:24:58 am
content: Quote from: Mrt12 on January 25, 2018, 08:14:29 pmI'm not sure if the two issues are related - there might be a test set issue and a power supply issue.Do you have an 85047A 6GHz test set or an 85046A 3GHz? The 6 GHz one has the doubler and the switches around that could be sticking perhaps?You could check the phase lock issue without the test set - unplug all of the cables to the test set including the one at the back - and then just connect RF out to the R input. To be safe put a 20dB attenuator inline too so you cannot overload the R input.That will take the test set out of play and force it into 3GHz mode. Then it should always phase lock no matter what you do. If it displays the same symptoms then perhaps there is something wrong in the source/receiver area of the analyser.If it is still a problem, then you can isolate to the source or receiver section. All of the receivers are the same so you can swap the R and A or B receivers around and if the problem is the same then you know it is the source. Before you do that however you should probably go through the source tune/cal steps in the service manual if you haven't done that already. This guy had an 8753C which was fixed by doing that:http://jvgavila.com/hp8753c.htm