HP 8711A: modifications, tweaks, refurbishing

I recently acquired a fairly well preserved HP 8711A network analyser. As sold, this is an economy model, offering only scalar measurements (although vector information can be acquired through the HP-IB bus).

Conversion

What makes this unit interesting, is that the hardware is the same as the never released 8712A, which has vector capabilities. Some changes in the bootrom allow the user to “convert” the unit, making it behave like a full fledged VNA.

Credits for this rom modifcation go to Massimo Porzio (IK1IZA). As far as I know, he is the one who took the time to figure this out. I also found a lot of information on the site of Michal Lewczuk (SP2XDM).

Before doing anything, a backup of the correction constants was made to disk.

Unit boot screen as received:

20160927_173814

I used the TL866 USB High Performance Programmer which can be bought online for around €40. Download the software while you wait for the package to arrive, download speed reminded me of the late nineties…

The bootrom with attached label (on the A1 CPU board, removal of the CRT/PSU module is necessary):

20161006_211100

Contents of the ROM at address 0x1FFA0 prior to modifications:

eeprom-before

After modifications:

eeprom

New bootscreen (SRL and fault location enabled as well):

20161114_171152

Smith chart as proof of vector capabilities:

20161114_171232

CRT realignment and brightness setting

Some adjustments on the CRT were done:

  • When looking from a normal viewing angle with the unit placed on the desk, the alignment of the options on the right of the screen seems “off” when compared to the location of soft buttons next to them.
  • The screen was rather dim.
  • Sizing of the display compared to the cutout in the front panel could be enlarged.

I marked the locations of the front panel cutout and the top and bottom buttons on the CRT:

20161031_091501

After disassembling the CRT/PSU module and attaching the PSU to the back, followed by some creative cabling, the unit was powered on while leaving access to the alignment potmeters:

20161031_094911

The positions of the potmeters before adjustment were marked:

20161031_093910

After adjusting the height/width and brightness, the screen looked much better.

Power supply patch

According to a ECN from HP, units with serials between A00000 and 3325A00941 need a 3W, 680Ω resistor between pin 9 and 16 on J5 in the power supply.

Before:

20161107_212030

Resistor added and pcb cleaned:

20161107_212732

Speaker “modification”

The A models of this network analyser had an issue where noise would get into the audio circuit, causing a high pitched, squeeling noise. When used in a silent environment this was really bothersome, so I first tried replacing the speaker by a version with a slightly different resonant frequency.

This didn’t help enough, so I ended up with this ugly (but fully working) solution:

20161031_103828

Cleaning and restoring the unit

A lot of time was spend cleaning and restoring the unit, as to give it as much of its original appearance as possible.

  • The inside of the case was cleaned, connectors on the backplane (which are notorious for causing problems with this model) were cleaned using a combination of MEK, IPA, soda, warm water, patience and lots of love.
  • Front panel and keypad were cleaned, and the yellowing of the plastic due to age and UV was reversed through the use of high concentration hydrogen peroxide. Dents, holes and cuts were fixed.
  • The vinyl was cleaned, restored and treated.
  • Internals of the disk drive were cleaned.

Documenting this is worth a separate post.

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45 thoughts on “HP 8711A: modifications, tweaks, refurbishing

  1. Bedankt voor de post Dieter! Knap gevonden, zal ernaar teruggrijpen als ik eens een zulke vind op een hambeurs of zo. 73 Bert, ON3VB

    • Heb de mijne (na zoeken) gevonden, in goeie staat, voor €400. Heb dit trouwens niet zelf uitgevonden, heb dat ondertussen toegevoegd…

        • Als jij uit Nederland komt zou dat wel eens kunnen ja…
          VNA mod werkt trouwens ook op de 8711C, moest je willen…

  2. Klopt…..jammer dat bij die A de voetjes niet meer zaten.
    Als het meezit zit morgen de Vector en optie 100 erin.
    Heb het impedantie probleem opgelost met 2 Mini-Circuits UNMP-5075+ pads scheelt je wel ca 11 dB.
    In de transmission connector zit een weerstand van 25 Ohm dus als je die vervangt heb je in ieder geval die kant wel 50 Ohm.
    De reflection kant is in zijn geheel 75 Ohm (daar moet ik nog een oplossing voor vinden)

    • Heb dezelfde minimum loss pads op de kop getikt, je bent inderdaad wel een dike 12dB kwijt. De hardline van de A3 assembly naar de front connectors is ook 75 ohm dacht ik, niet? Vraag me af of je er geraakt met enkel die 25 ohm weerstand weg te halen. Het is te proberen natuurlijk…
      Als je binnen een (heel) beperkte band blijft zijn er wel impedantie transformers die pakken minder verlies hebben, maar dan heb je natuurlijk een heel beperkte bandbreedte…

      • Hoi,

        Heb met een andere VNA gemeten en die rechterkant is 50 Ohm (gehele rigid losgenomen en weer afgesloten met mijn cal load)
        Meet maar met een Ohm meter de rechter connector door je zal zien dat je 25 Ohm meet.
        De linker rigid heb ik op dezelfde wijze getest en die maakte geen contact met de 50 Ohm SMS connectoren de binnen kern is dunner (dus 75 Ohm)
        Ook zal je zien dat de linker connector slechts een doorverbinding is.

        Deze HP 8711C is vandaag ook een HP 8712C geworden.

        Tevens heb ik ook een 8.4 Inch VGA scherm besteld via Ebay (zie EEVBLOG) en die wil ik er ook gaan inbouwen.
        Een stuk zwaar wegend groen oplichtend glas is niet meer van deze tijd en door het nieuwe scherm krijgt de analyzer een stukje moderner uiterlijk.

        • Wist niet dat de CRT-LCD mod ook ging voor deze.
          Krijg je dan je signal via de connector achteraan? Dan heb je nog een conversie van PAL naar RGBHV nodig, of niet?

    • Hey Marcel, die thread had ik ook al gevonden maar de 8711A heeft geen VGA out maar enkel composite. Vandaar mijn vraag naar de composite naar RGBHV conversie. Blijkbaar heeft de C behalve een netwerkpoort ok nog een VGA aansluiting.
      Misschien moet ik eens proben op de print of er ergens toch nog iets te vinden is, maar ik vrees er voor.
      Misschien moeten we verder communiceren via email?

  3. Beste Dieter,

    Goed idee, mijn email adres is je waarschijnlijk al bekend, zo niet dan geef ik je het alsnog even door.

    Met vriendelijke groet en in afwachting van je reactie,
    Marcel

  4. Hallo Dieter,

    Kan jij mij nog even je mail adres opnieuw sturen?
    Zit bij een andere internet provider.

    Met vriendelijke groet,

    Marcel

  5. Hi there,
    I’m Massimo IK1IZA.
    I wrtite this post, just to inform you and any other who want to apply the mods to an HP8711C, that this FW mods don’t work on it! (on the HP8713C they works anyways).

    To make them work on the HP8711C, you must change the first two bytes on the second line of configuration record from FFh, FFh to 00, 01h (the one that in the photos above were at addresses 1FFB0h and 1FFB1h, for a 16 bytes per row hex editor such the one in the photos above, they are the ones under the bytes with value 02h and 04h on the first configuration record line).

    Leave the other FFh bytes as per the HP8711A mods.

    Have a great day.

    Massimo – IK1IZA

    • Hoops!
      I just realized that I wrote:
      “Leave the other FFh bytes as per the HP8711A mods.”
      No! It was intended:
      “Leave the other 00h bytes as per the HP8711A mods.”

      Sorry.

      Massimo

      • Hello Massimo,

        Thank you for your comment! Great to hear that it can work for a 8711C as well.

        I`m sure a lot of people are very grateful to you for your help, tips and comments.
        I think you are also the one who assured me that the squeeling noise I heard on my unit was perfectly normal for the earlier models. If not for you I could have spent a lot of time searching for an issue/problem that simply didn’t exist.

        My next projects will be a HP 8640B restoration, the BITX40 with some mods and learning CW. I’m still searching for SA bargain (but I’m not the only one, of course…).

        Thanks and 73’s,

        Dieter ON4DD

        • Hi Dieter,
          I didn’t read you message until today because for a strange reason I had not any notification about it.
          Anyways, I’m glad reading that my time spent on this is still useful for someone.
          I wish you the best enjoyment doing all your next projects and I hope everything will be right at the first try (even if Murphy’s laws usually tell a different story, sigh!).
          Have a great day.

          73

          Massimo – IK1IZA

      • Massimo, very interesting reading, just got hold of a 8711c wich i plan to modify according to your findings :-)
        Is there a way to get your services by any chance if i send you the contents of my rom via e-mail, if you can look at it and send it back to me edited?
        Also some of the guy´s talk about changing the impedance from 75 to 50 Ohms, i have had a dicussion with Agilent which states that it´s just the connectors and hard coax lines that is 75 Ohm, but that they are spot welded to the receiver board and hard to get out, otherwize it would not be a problem changing the system from 75->50 Ohm..

        73´s
        and best regards
        Anders
        ( Sm7Hce )
        anders@lm-konsult.se

        • Hi Anders,
          yes, if you send me the binary content of your bootrom (or better bootflash), I can do the mods for you.
          Even if it’s just a precautionary principle, I suggest you to keep the original bootflash chip until you see the instrument working right with the new bootflash. For this, If I were you I would buy a new flash chip and use it for the mods keeping the original in the drawer :-)
          Unluckily (AFAIK), the 75 ohms machines have a different frontend indeed. Now I’m at office and I’ve not here the schematics, but until at home I could take a look to them and see if I remember correctly or not about that.
          If you already don’t have the schematics, I’ll send them to you.
          Always if I remember correctly, the schematics refer to version B of the family, but an HP engineer ensured me that except for the later ES version the only changes between versions were about the CPU board.

          Have a great day.

          Massimo

        • Thanks Massimo, and yes, i would also suggest putting the new program on a new chip :-), otherwize “murphy” will be there

          – Assumption is the mother of all F-ups :-):-)

          i appriciate the offer to do it for me, and i will take you up on that, i just have to find a suitable programmer to use… puhh, must have been 20 years ago one used something like that – any suggestions?

          According to the tech i talked to, the only difference between 50/75 Ohm is the connectors on the motherboard (wich are spotwelded he claims) the “hard” coax and the frontconnectors, otherwize its all the same.. ofcourse one can change them to coax but then there probably will be some losses and frequency problems further up 1Ghz,…. really good cables are hard to find….

          Please send me the schematics = very nice :-), dont have them yet, saw something on agilents web page, but havent downloaded anything ..

          – And if you can send me a e-mail so i know where to sent the file

          I wish you and the rest of the gang, a wonderful evening

          Best regards
          / Anders

  6. one thing that stroke me, is the 8711,12,13,14 basicly the same unit or have they fitted a wider oscillator on the 13&14 for 3Ghz… or is this also software?

    • Hi Anders,

      I just sent you the schematics via the WeTransfer service because their size were huge (abt 90Mbytes).
      Take a look to your mailbox for the instructions to download them.
      The link for download it will be there for the next 7 days.

      Effectively despite the 50 ohms and 75 ohms receivers have different schematics numbers, the schematics looks the same to me.

      The 1.3GHz machines have a completely different synthesizer board and couplers, so unluckily it’s not just a SW difference.

      Have a great day.

      73

      Massimo IK1IZA

      • Hi Massimo, got the files, thank you :-)

        i kindda figured that was the issue with the 3Ghz models, i´ll get back to you shortly

        thanks

        73
        Anders

        • Hi Anders,
          enjoy your task and have a great day.

          By the way, I think that the following link should be available in the next 7 days to anybody who needs the HP871xx schematics.

          https://we.tl/p90SwKxPCr

          All the best.

          73

          Massimo

        • Anders,
          If you ever get around to adapting your unit to 50 ohms, please let me know. That would be great.

          Regards,
          Dieter

        • Hi Dieter, i certanly will let you know :-)

          Have a nice weekend

          Best regards
          / Anders

        • Hi Anders,
          I thought a little more about the 50/75ohms conversion.
          And effectively, there is no reason to have different receivers for the two versions because they are coupled to the instrument ports via directional couplers, which coupled line has no need to have the same impedance of the coupler passing through line.
          You should take a look to the source output stage and the couplers themselves. I guess they should be impedance related components indeed.
          The source could have a minimum loss impedance matching adaptor at its output.
          While the couplers could be different in the main line and termination loads.

          By the way, some times ago I tried the Smith chart 75ohm measurement using a couple of 50/75ohms adapters. Well, after having done the port calibration to de-embedding them, I had been able to work without appreciable issues.

          Have a great day

          Massimo

        • Hi Massimo

          Yes i agree, i´m using the 11852A low loss pads for my unit wich works just fine after calibration, you just loose approx 6db in signal, but i doesent make much difference in my case, so why am i interested in the conversion…

          – Because its fun :-):-):-)

          Many systems are the same due to R&D costs and it´s of course cheaper to put this in software rather then new hardware when designing, and i appriciate this, however when we are dealing with 25 year old systems that is discontinued, it´s fun to play around – i personally cannot afford to take my hobby to the 50.000 Euro level to buy a new one so…..

          I will definitly check out the schematics and se if there is a “fix” for it, it seems that there is some interest for this in the community to :-)

          BTW – wich reader/programmer do you use for this eprom? – have to “shop around” worked many, many years ago with servicing home computers, vcr´s etc.. and at the time we had a station for this, but this is now long gone and if it still exists it is probably a PET bottle or something by now :-)

          Have a nice evening
          73
          / Anders
          Sm7Hce

        • Hi Anders,
          sorry for the late reply, but yesterday I spent my time fixing my Rohde & Schwarz SME03 LCD. It had the endemic horizontal black lines issue. Those times the LCD frontal metallization lines were connected through a damned thin plastic flat ribbon just attached with am adhesive tape on the controller PCB and with a glasslike glue on the LCD!
          The issue is unsolvable for me, so I bought for few Euro a working CMD57 (a useful for nothing else than as an GSM repairing instrument) and executed an LCD “transplant”.
          You wrote:

          “– Because its fun :-):-):-)”

          I fully agree, the expensive instruments are just for professional use, let the companies buy them and let us buy their “oldies” for few bucks.
          Most (practically almost all) of my home workshop instruments had to be fixed (and sometimes hacked).
          By the way, I recently bought an Advantest R3671 Signal Analyzer (13GHz SA + 3GHz digital SG) that I hacked to get a R3681 (32GHz SA + 6GHz digital SG). As you stated, the machines were the same and had just a serial EEprom on each board which other than the board settings and calibrations got the extensions limits hidden into the board name!
          In that case everything works great, but the SA has the input attenuator limited to 15GHz so the SWR at the input isn’t so good at 32GHz. But I got it for free and the readings are into the specs up to 32GHz anyways, so who cares? :-)

          For the bootflash I used a very old Needhams EMP10 programmer, but it’s a DOS only device. Dieter’s suggestion should be better, just look at the flash model of your NA to see if it’s supported, that because as far I know the chips changed version by version.

          Have a great day.

          73

          Massimo

        • Massimo, great :-), it lookes like you and me are the same haha, i also have loads of refurbished equipment bought online at various auctions :-)

          Just finished dissasembly of my 8711c, but it looks completely different then the pic´s ive seen online, lots of surface mount and 8712 board w. AM28f020 as boot rom, i´ll send you some pics to your mail, if this one looks the same in software i dont know, but i´ll need a different programmer :-( luckely i havent bought one yet

          Your an radioamateur i guess, what are you using?

          Best regards
          / Anders

      • Hi Anders,
        I’m radio amateur, my call is IK1IZA but I’m little or not active in these days.
        Every time I’m at my home workshop (like now) while I’m doing my task I listen to the local radio club VHF frequency,
        Until last month I also had a three band home made delta loop, but after 26 years of its standing on the roof I had to dismantle it because of its age (everything passes sigh!).

        About the Am28F020, Dieter’s suggested TL866 programmer supports it.

        Anyways, my email is mporzio@teletu.it

        Have a great Sunday.

        Massimo

        • Hi again Massimo, i´m sending you the pics in 2min, are currently downloading my phones gallery wich took 30min.. :-) yes to the progrmmer, it only need to take the PLCC casing

          / Anders

  7. Also, i´m thinking – these original coax hard lines are extremely accurate, if one just dealing in amateur frequencys, it may be ok to use some good coax cable, but one can very easy run in to problems like stray capacitance etc, when going further up the in the Ghz zone, so for those who try and change this it´s worth to know..

    / Anders

      • Hello, ill try and see in i can find one locally, replied to Dieter about this before sorry :-) – have the PLCC casing on the AM

        Have a nice day

    • If you are talking about the 8711 inner HL I don’t think they are critical indeed.
      Just one consideration about the cables to de-embed for connect the DUT to the VNA.
      Take always account that when you use cables which length is close to 1/4 lambda (corrected for the cable speed of course) for S11 the de-embedding works bad or it doesn’t work at all at 1/4 lambda. That because @1/4 lambda open, close and load as seen by the couplers are always matched.
      (I write this because one time I’ve been deceived by the use of cables at that length, note also that the lenght I’m writting about is those between the inner coupler port and the cable end at which you move the reference plane by de-
      embedding)

      Again, have a great day.

      Massimo

        • Hi Massimo, finally got the holder for the flash memory, i have sent you the files on e-mail

          / Best regards

          / Anders

      • Massimo,

        I don’t really understand what you are talking about concerning the de-embedding of the DUT. Could you explain further?

        Also, may I ask what you use the SA >15GHz for? What kind of circuits/systems are you working on?

        Regards,
        Dieter

      • Hi Massimo, finally got the holder for the flash memory, i have sent you the files on e-mail

        / Best regards

        / Anders

        • Hi Anders,
          I sent you the modified file.
          Let me know how it works.

          Have a great day.

          Massimo

    • Anders,

      Same person. Fozzyvis is an old alias. Just changed my settings to show my name instead of the alias.

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