First Bench Multimeter - Fluke 8840a vs HP 3478a

[gryffinwings]

Hi guys, new here, I'm looking at getting some insight and advice on these 2 bench multimeter, the Fluke 8840a, and the HP 3478. So far the main issues I've seen with these is that the Fluke 8840a can have issues with a dim display due to being a VFD. The HP 3478a, on the other hand, will need a battery replacement to maintain the SRAM.

Thoughts on either Bench DMM, accuracy between the two, recommendations, etc, appreciate any additional insight on these 2 DMMs.

[jxjbsd]

The beautiful VFD display is still the decisive factor in choosing 8840A.

[gryffinwings]

The beautiful VFD display is still the decisive factor in choosing 8840A.

That is something I am considering, I love the way the display looks.

[pqass]

I've been VERY happy with my HP3478A that I've acquired in February of this year. 
Within the first two weeks I've managed to build a Arduino-based GPIB interface, download the the calibration data, and replace the battery thanks to the help of this forum.  But I still have 4 RIFA caps to replace.

I really like the 30mA range that can read down to 100nV (although it's a bit jumpy); it can read thermocouples directly!  I've only had hand-held meters so this was a step up for me.

Regarding the spec differences, the 3478A is a 300K count meter vs. 100K for the Fluke. Check out the meter spreadsheet here: https://www.eevblog.com/forum/testgear/multimeter-spreadsheet/ 

Although a bright VFD is nice, I cured the hard-to-read LCD problem with an IKEA JANSJO lamp.
I think I did alright for US$100 price I paid for it. 

[Kleinstein]

The 3478 has high Z only up to a little over 3 V. The Fluke 8840 has high Z up to 20 V. With the Fluke meter AC is optional.
I found the HP meter relatively easy to use, the LCD is sometimes a little difficult to read with poor light or from some angles, but still OK. AFAIK one still needs cold junction compensation, but the resolution is good, thanks to 30 mV range.

[gryffinwings]

I've been VERY happy with my HP3478A that I've acquired in February of this year. 
Within the first two weeks I've managed to build a Arduino-based GPIB interface, download the the calibration data, and replace the battery thanks to the help of this forum.  But I still have 4 RIFA caps to replace.

I really like the 30mA range that can read down to 100nV (although it's a bit jumpy); it can read thermocouples directly!  I've only had hand-held meters so this was a step up for me.

Regarding the spec differences, the 3478A is a 300K count meter vs. 100K for the Fluke. Check out the meter spreadsheet here: https://www.eevblog.com/forum/testgear/multimeter-spreadsheet/ 

Although a bright VFD is nice, I cured the hard-to-read LCD problem with an IKEA JANSJO lamp.
I think I did alright for US$100 price I paid for it.

The little projects that you've done for the 3478a is pretty awesome, also instead of GPIB did you mean HP-IB? That is definitely something I would be interested in. The battery part has me a little nervous, I've been watching youtube videos, not sure what route I would go exactly as I do not have all the extra equipment for isolation.

[Mp3]

I am also looking to get my first bench meter and the non backlit display is the only reason I haven't jumped on a 3478a. Though, i've managed with no backlight on my Fluke handheld meter all these years.

I'm confused if it would be compatible with the leads from my Fluke 101 though.

I do worry a bit about the EPROM and all the old IC's on the 3478a. The calibration being in SRAM is bad enough, but not the end of the world.

[nctnico]

I'd buy neither. Get a Vici VC8145 bench meter instead. It has more features and a way better display.

[Kleinstein]

I am also looking to get my first bench meter and the non backlit display is the only reason I haven't jumped on a 3478a. Though, i've managed with no backlight on my Fluke handheld meter all these years.

I'm confused if it would be compatible with the leads from my Fluke 101 though.

I do worry a bit about the EPROM and all the old IC's on the 3478a. The calibration being in SRAM is bad enough, but not the end of the world.

I would not worry so much about the EPROM - AFAIK there are images around, so one could get a replacement.
The tricky parts are more the HP hybrid chips and special resistor networks. They don't fail very often, but are hard to get (more like a broken meter for spares).
However essentially all higher grade DMMs use some custom chips or resistors. The fluke meter also has a custom chip and quite some critical resistors in the ADC.

[pqass]

"...did you mean HP-IB?" Yes, I use HPIB/GPIB interchangeably.

Before I did anything, I wanted to have a copy of the calibration data.  This is what I did...

Thanks to WaveyDipole (see:https://www.eevblog.com/forum/projects/ar488-arduino-based-gpib-adapter/), I connected my Arduino as per the simplest configuration in Appendix A (see:https://github.com/Twilight-Logic/AR488/raw/master/AR488-manual.pdf).  Installed Version 0.48.08 of his software, verified connectivity with the meter and got familiar with the command-set.

I then created the following program (a.c):

Code: [Select]

    #include <stdio.h>
    #include <unistd.h>
    void main() {
        for(int i = 0; i < 256; i++) {
            printf("W\033%c\r++read\r", i);
            fflush(stdout);
            usleep(500000);
        }
    }

Before executing the ./a program, I started recording to a gtkterm log file (newstcal1.log).
    $ gcc -o a a.c
    $ ./a >>/dev/ttyACM0
    $ awk <newestcal1.log '{printf "%s", substr($0,1,1);}' >newestcal1.cal
The last line above copies the first character of each log line to a "cal" file.

For better readability (broken into records and hexdumped) execute:
    $ cat newestcal1.cal|od -A x -t x1z -w13 --skip=1

000001 40 40 40 42 48 47 43 4c 4d 40 42 4d 40  >@@@BHGCLM@BM@<      30 mV DC         // 0
00000e 40 40 40 40 42 48 43 4c 4c 42 41 4d 47  >@@@@BHCLLBAMG<      300 mV DC        // 1
00001b 40 40 40 40 40 43 42 45 43 41 45 4e 4c  >@@@@@CBECAENL<      3 V DC           // 2
000028 49 49 49 49 49 44 43 4c 4c 4f 4d 49 47  >IIIIIDCLLOMIG<      30 V DC          // 3
000035 49 49 49 49 49 49 42 45 43 4e 4d 4a 44  >IIIIIIBECNMJD<      300 V DC         // 4
000042 40 40 40 40 40 40 40 40 40 40 40 4f 4f  >@@@@@@@@@@@OO<      <not used>       // 5
00004f 49 49 49 40 43 48 42 43 42 43 43 4c 4c  >III@CHBCBCCLL<      AC V             // 6
00005c 49 49 49 49 43 47 40 45 45 40 44 4c 43  >IIIICG@EE@DLC<      30 Ohm 2W/4W     // 7
000069 49 49 49 49 49 44 40 45 44 42 4e 4b 45  >IIIIID@EDBNKE<      300 Ohm 2W/4W    // 8
000076 49 49 49 49 49 49 40 45 41 41 4d 4b 45  >IIIIII@EAAMKE<      3 kOhm 2W/4W     // 9
000083 49 49 49 49 49 49 40 45 40 40 42 4c 42  >IIIIII@E@@BLB<      30 kOhm 2W/4W    // 10
000090 49 49 49 49 49 49 40 45 41 4e 4f 4a 46  >IIIIII@EANOJF<      300 kOhm 2W/4W   // 11
00009d 49 49 49 49 49 49 40 45 4f 41 42 4b 42  >IIIIII@EOABKB<      3 MOhm 2W/4W     // 12
0000aa 49 49 49 49 49 49 40 45 42 44 40 4b 4e  >IIIIII@EBD@KN<      30 MOhm 2W/4W    // 13
0000b7 49 49 49 49 49 48 44 4d 4e 4d 4c 49 42  >IIIIIHDMNMLIB<      300 mA DC        // 14
0000c4 40 40 40 40 40 40 44 4d 4c 43 40 4d 4f  >@@@@@@DMLC@MO<      3A DC            // 15
0000d1 40 40 40 40 40 40 40 40 40 40 40 4f 4f  >@@@@@@@@@@@OO<      <not used>       // 16
0000de 49 49 49 40 43 48 43 44 42 42 4c 4c 42  >III@CHCDBBLLB<      300 mA/3A AC     // 17
0000eb 40 40 40 40 40 40 40 40 40 40 40 4f 4f  >@@@@@@@@@@@OO<      <not used>       // 18
0000f8 40 40 40 40 40 40 40 40                 >@@@@@@@@<


I then verified each of the records above using the following pseudo-code (checksum is in [11][12] positions of each entry):

Code: [Select]

    for(byte cksum = 0, int j = 0; j < 19; j++, cksum = 0) {
        for(int i = 0; i < 11; i++)
            cksum += (entry[j][i] & 0xf);
        cksum += entry[j][11] << 4
        cksum += entry[j][12] & 0x0f
        if (cksum == 0xff) then SUCCESS!!!!
    }
1st entry example (ignore the leading nibble): (0+0+0+2+8+7+3+c+d+0+2)+d0+00 == ff

Once that was out of the way, I moved onto the hardware. 
After studying the schematic, I determined that the simplest and safest solution was, WITH THE 3478A POWER PLUG DISCONNECTED, to solder a "pig tail" with series 330R resistor and signal diode to the cathode of CR500 and ground-side of a nearby bypass cap.  Before committing, I checked that I had the right trace by using my hand-held meter to confirm that it had +3V (lithium battery) when the 3478a was powered off and +5V (meter main digital power rail) when the 3478a was powered-on. 



I then turned on the 3478a to confirm the calibration was still okay. It was, and the hard part was over.
WITH THE 3478A POWER PLUG DISCONNECTED, I then attached a battery holder with 3 AA batteries to the pigtail.  Again, using my hand-held meter, I confirmed that the cathode of CR500 had +4.5V with the new battery holder attached and +3V (lithium battery) without it.  I left the new AA holder attached, then proceeded to cut-out the old lithium battery (at the spot-welded points) leaving two lead stumps.  Again, I then turned on the 3478a to confirm the calibration was still okay. It was.

WITH THE 3478A POWER PLUG DISCONNECTED, I then soldered in the new lithium battery and disconnected the AA battery holder.  I left in the pigtail for the next guy.

No isolation [equipment] was required. Just planning and an extra battery.

P.S.
Much thanks to this thread: https://www.eevblog.com/forum/repair/hp-3478a-how-to-readwrite-cal-sram/

[Mp3]

@pquass- Great work and writeup, tyvm! I don't really wanna mess with still working test equipment too much, but i was thinking about replacing a few of those filter caps with fresh ones while i was in there.

I'd buy neither. Get a Vici VC8145 bench meter instead. It has more features and a way better display.

This meter looks nice, but it's about $150 at its cheapest, and I am able to get a self-test verified 3478a for $40.
I had considered all these options before, but the Fluke is just too old for me. The 3478a is at least as old as I am.

I am also looking to get my first bench meter and the non backlit display is the only reason I haven't jumped on a 3478a. Though, i've managed with no backlight on my Fluke handheld meter all these years.

I'm confused if it would be compatible with the leads from my Fluke 101 though.

I do worry a bit about the EPROM and all the old IC's on the 3478a. The calibration being in SRAM is bad enough, but not the end of the world.

I would not worry so much about the EPROM - AFAIK there are images around, so one could get a replacement.
The tricky parts are more the HP hybrid chips and special resistor networks. They don't fail very often, but are hard to get (more like a broken meter for spares).
However essentially all higher grade DMMs use some custom chips or resistors. The fluke meter also has a custom chip and quite some critical resistors in the ADC.

Makes sense. But custom resistors? I thouht all resistors were "off the shelf" so to speak....
The EPROM I didn't realize is a standard 64kb, i thought at first it was one of the older ones in a 26 pin package.
Hmm, i could program a spare 27c64 OTP with the image just as a preventative measure. Hard to say if it's worth waiting until the electrons get loose from the EPROM.

[pqass]

Shrouded banana plugs WILL NOT fit in the 3478a.

I appear to have a ROM, not EPROM in my '88 vintage 3478a.
See previous post picture.

[Mp3]

Shrouded banana plugs WILL NOT fit in the 3478a.

I appear to have a ROM, not EPROM in my '88 vintage 3478a.
See previous post picture.

I noticed that, from checking them out on google image search, seems a variety of chips was used, i saw at least 3 different brands looking at google image results. I'll hope there is an OTP chip in mine. As long as they all use the same binary, its all good.

[pqass]

"...thinking about replacing a few of those filter caps..."

My filter caps seem fine so I wasn't thinking about touching them.
Although, I vaguely remember reading in the forum it may improve the meter readings.

But the 4 RIFA caps on either side of the transformer have got to go.
They show hair-line cracks.    Good thing I don't use the meter in the shower!

[Kleinstein]

Makes sense. But custom resistors? I thouht all resistors were "off the shelf" so to speak....
The EPROM I didn't realize is a standard 64kb, i thought at first it was one of the older ones in a 26 pin package.
Hmm, i could program a spare 27c64 OTP with the image just as a preventative measure. Hard to say if it's worth waiting until the electrons get loose from the EPROM.

In the 3478 the critical resistors are inside the 2 custom hybrids. So likely no extra custom resistors in this meter - but as part of the hybrids. So in theory these can also fail from resistor drift. However  with the integrating ADC resistor drift would mainly cause gain changes that can be compensated to a large extend.
For the old ROMs there is the option to use adapters to a EPROM can be used in the ROM socket.

Replacing the filter caps is mainly for the possible smell and smoke in case they fail. Don't expect any change in noise. It would be only right before the magic smoke escapes that a bad cap may also add noise.

[Back2Volts]

The beautiful VFD display is still the decisive factor in choosing 8840A.

That is something I am considering, I love the way the display looks.

I have one and the display is very nice.   It is seating next to a 805A, and what a difference!

[Mp3]

Thanks for the clarification on the resistor networks. I 'm not terribly concerned about it, unless the meter begins to act wild.

Yeah, i have no intention of replacing the caps expecting it to make any difference in the operation of the multimeter. I figured they're old, crusty, dried out and it wouldn't hurt to replace them before they give out, if I'm going to have this unit in frequent operation.  (C761 - 3300uf 25v , C711 - 1000uf 25v , C703 & C702 - 330uf 50v)

i didn't realize you can get access to the bottom of the main board without removing it from the chassis, so this should be very easy to do i think.

BTW - I am planning on DIY'ing some test leads for my 3478a. Part of the reason I got it for such a low price was it was just the unit by itself. I was planning on using some spare unsheathe banana plugs I have on hand, since they're nice quality and I already have them. But they're the gold plated A/V type by Mediabridge. I didn't think there would be any problem using these - as long as they fit at all - but then I came across this post by one of the designers of the 3478, suggesting to use copper tubing for a DIY plug? Any thoughts on this...? https://groups.io/g/HP-Agilent-Keysight-equipment/topic/29423423?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,40,29423423

I know unshrouded is dangerous for high voltage but I can't remember the last time I measured anything higher than 24VAC, and I have my handy-dandy Fluke 101 just in case i find myself needing to measure 600V.

[gryffinwings]

"...did you mean HP-IB?" Yes, I use HPIB/GPIB interchangeably.

Before I did anything, I wanted to have a copy of the calibration data.  This is what I did...

Thanks to WaveyDipole (see:[url]https://www.eevblog.com/forum/projects/ar488-arduino-based-gpib-adapter/[/url]), I connected my Arduino as per the simplest configuration in Appendix A (see:[url]https://github.com/Twilight-Logic/AR488/raw/master/AR488-manual.pdf[/url]).  Installed Version 0.48.08 of his software, verified connectivity with the meter and got familiar with the command-set.

I then created the following program (a.c):

Code: [Select]

    #include <stdio.h>
    #include <unistd.h>
    void main() {
        for(int i = 0; i < 256; i++) {
            printf("W\033%c\r++read\r", i);
            fflush(stdout);
            usleep(500000);
        }
    }

Before executing the ./a program, I started recording to a gtkterm log file (newstcal1.log).
    $ gcc -o a a.c
    $ ./a >>/dev/ttyACM0
    $ awk <newestcal1.log '{printf "%s", substr($0,1,1);}' >newestcal1.cal
The last line above copies the first character of each log line to a "cal" file.

For better readability (broken into records and hexdumped) execute:
    $ cat newestcal1.cal|od -A x -t x1z -w13 --skip=1

000001 40 40 40 42 48 47 43 4c 4d 40 42 4d 40  >@@@BHGCLM@BM@<      30 mV DC         // 0
00000e 40 40 40 40 42 48 43 4c 4c 42 41 4d 47  >@@@@BHCLLBAMG<      300 mV DC        // 1
00001b 40 40 40 40 40 43 42 45 43 41 45 4e 4c  >@@@@@CBECAENL<      3 V DC           // 2
000028 49 49 49 49 49 44 43 4c 4c 4f 4d 49 47  >IIIIIDCLLOMIG<      30 V DC          // 3
000035 49 49 49 49 49 49 42 45 43 4e 4d 4a 44  >IIIIIIBECNMJD<      300 V DC         // 4
000042 40 40 40 40 40 40 40 40 40 40 40 4f 4f  >@@@@@@@@@@@OO<      <not used>       // 5
00004f 49 49 49 40 43 48 42 43 42 43 43 4c 4c  >III@CHBCBCCLL<      AC V             // 6
00005c 49 49 49 49 43 47 40 45 45 40 44 4c 43  >IIIICG@EE@DLC<      30 Ohm 2W/4W     // 7
000069 49 49 49 49 49 44 40 45 44 42 4e 4b 45  >IIIIID@EDBNKE<      300 Ohm 2W/4W    // 8
000076 49 49 49 49 49 49 40 45 41 41 4d 4b 45  >IIIIII@EAAMKE<      3 kOhm 2W/4W     // 9
000083 49 49 49 49 49 49 40 45 40 40 42 4c 42  >IIIIII@E@@BLB<      30 kOhm 2W/4W    // 10
000090 49 49 49 49 49 49 40 45 41 4e 4f 4a 46  >IIIIII@EANOJF<      300 kOhm 2W/4W   // 11
00009d 49 49 49 49 49 49 40 45 4f 41 42 4b 42  >IIIIII@EOABKB<      3 MOhm 2W/4W     // 12
0000aa 49 49 49 49 49 49 40 45 42 44 40 4b 4e  >IIIIII@EBD@KN<      30 MOhm 2W/4W    // 13
0000b7 49 49 49 49 49 48 44 4d 4e 4d 4c 49 42  >IIIIIHDMNMLIB<      300 mA DC        // 14
0000c4 40 40 40 40 40 40 44 4d 4c 43 40 4d 4f  >@@@@@@DMLC@MO<      3A DC            // 15
0000d1 40 40 40 40 40 40 40 40 40 40 40 4f 4f  >@@@@@@@@@@@OO<      <not used>       // 16
0000de 49 49 49 40 43 48 43 44 42 42 4c 4c 42  >III@CHCDBBLLB<      300 mA/3A AC     // 17
0000eb 40 40 40 40 40 40 40 40 40 40 40 4f 4f  >@@@@@@@@@@@OO<      <not used>       // 18
0000f8 40 40 40 40 40 40 40 40                 >@@@@@@@@<


I then verified each of the records above using the following pseudo-code (checksum is in [11][12] positions of each entry):

Code: [Select]

    for(byte cksum = 0, int j = 0; j < 19; j++, cksum = 0) {
        for(int i = 0; i < 11; i++)
            cksum += (entry[j][i] & 0xf);
        cksum += entry[j][11] << 4
        cksum += entry[j][12] & 0x0f
        if (cksum == 0xff) then SUCCESS!!!!
    }
1st entry example (ignore the leading nibble): (0+0+0+2+8+7+3+c+d+0+2)+d0+00 == ff

Once that was out of the way, I moved onto the hardware. 
After studying the schematic, I determined that the simplest and safest solution was, WITH THE 3478A POWER PLUG DISCONNECTED, to solder a "pig tail" with series 330R resistor and signal diode to the cathode of CR500 and ground-side of a nearby bypass cap.  Before committing, I checked that I had the right trace by using my hand-held meter to confirm that it had +3V (lithium battery) when the 3478a was powered off and +5V (meter main digital power rail) when the 3478a was powered-on. 

(Attachment Link)

I then turned on the 3478a to confirm the calibration was still okay. It was, and the hard part was over.
WITH THE 3478A POWER PLUG DISCONNECTED, I then attached a battery holder with 3 AA batteries to the pigtail.  Again, using my hand-held meter, I confirmed that the cathode of CR500 had +4.5V with the new battery holder attached and +3V (lithium battery) without it.  I left the new AA holder attached, then proceeded to cut-out the old lithium battery (at the spot-welded points) leaving two lead stumps.  Again, I then turned on the 3478a to confirm the calibration was still okay. It was.

WITH THE 3478A POWER PLUG DISCONNECTED, I then soldered in the new lithium battery and disconnected the AA battery holder.  I left in the pigtail for the next guy.

No isolation [equipment] was required. Just planning and an extra battery.

P.S.
Much thanks to this thread: [url]https://www.eevblog.com/forum/repair/hp-3478a-how-to-readwrite-cal-sram/[/url]

Thank you so much for the write-up!

I'm also not sure what your are referencing in this "to solder a "pig tail" with series 330R resistor and signal diode to the cathode of CR500 and ground-side of a nearby bypass cap. " Could you explain this part a little more clearly, what parts you are you referencing? and where they go, and also where you ended up solving the battery setup to.

[PixieDust]

Are the HP meters region specific in terms of socket voltage? I can't figure out if there's some switch to select a different voltage like there is on the fluke.

[Venturi962]

HP 3478A is line switchable, you'll have to open it up to do so.

Video from VoltLog on the subject:

[pqass]

 ...snipped subquote...

Thank you so much for the write-up!

I'm also not sure what your are referencing in this "to solder a "pig tail" with series 330R resistor and signal diode to the cathode of CR500 and ground-side of a nearby bypass cap. " Could you explain this part a little more clearly, what parts you are you referencing? and where they go, and also where you ended up solving the battery setup to.

I've been meaning to do a writeup for this forum but also to print and include in the meter itself for the next guy (which will likely be me).

The "pig tail" is the white+red wire lead pair with a 100mil female connector on one end and a 330R resistor+diode on the red wire on the other end.

See top view image below on how I've attached it; red wire (after my diode) to the CR500 diode (cathode side) and white wire to a nearby bypass cap (GND side). 



Before cutting-out the old soldered-in lithium cell, the female connector of the pigtail is attached to any battery that is greater than 3V but less than 5V. In my case, I used a 3 cell AA battery holder (which is nominally 4.5V).  Being a different voltage (higher than the lithium battery) allowed me to confirm with a hand-held multimeter that pin 22 of the RAM was actually getting its voltage source from the pig-tail battery.  After the lithium battery is replaced, you can remove the temporary battery holder (leaving the pigtail, as shown, in for the next time).

Basically, I've replicated the same "wired-OR" circuit that the soldered-in lithium battery uses to gate its voltage onto pin 22 when the main 5V power rail is turned off.  See BT701, R765, CR764 in Figure 7-G-6.

DISCLAIMER: I've got a 2619Axxxx serial unit which seems to correspond to the 2nd set of schematics in the service manual located just before Appendix A.  Your unit may be earlier. In which case, my CR500 is equivalent to CR520 as it appears in the 1st set of schematics in Figure 6-5.  I don't know if CR520 is similarily placed in these earlier boards.

https://www.qsl.net/n9zia/test/HP3478_Service_Manual.pdf

[gryffinwings]

Well, it looks like I'm getting an HP 3478a soon, it just seems to be a lot more of them available at the price I would like to pay. After that, all I need will be an Oscilloscope and a Power Supply.

Thank you for all the information, I feel much more confident replacing the battery in an HP 3478a and not messing up the calibration data.

[nctnico]

Have you ever used a  HP 3478A? The LCD display is just horrible to read. Get something with backlight, VFD or LED. Read my previous suggestion; that is what I ended up with after a similar search like yours. Old DMMs just don't have the bells & whistles modern DMMs have. Older DMMs typically seem to have low current handling abilities too. 3A is quite limited.

[pqass]

Have you ever used a  HP 3478A? The LCD display is just horrible to read. Get something with backlight, VFD or LED. Read my previous suggestion; that is what I ended up with after a similar search like yours. Old DMMs just don't have the bells & whistles modern DMMs have. Older DMMs typically seem to have low current handling abilities too. 3A is quite limited.

Well, sure you could always spend more to get more features. 
But I can buy three 3478s (~US$135) for every 34401 (~US$400) on eBay.
They both have the same LM399 reference, are 300k count, and have a 30 or 100mV low DC range with 100nV resolution!  Sure, the 34401 is a more accurate, overall better meter but for me, the 3478 is more than good enough to work on op amp and other analog circuits. It gave me 3 extra right-hand digits compared to my hand-held meters.

The display readability can be solved with a clip-on LED goose-neck task light or even an HPIB-connected Arduino-based LED display (see AR488 project elsewhere on this forum) .  Some guy elsewhere on the forum even reverse-engineered the LCD protocol and replaced it with an LED equivalent!  It seems quite hack-able for a hobbyist.

Of course, I don't do professional work so price matters to me.

[PixieDust]

HP 3478A is line switchable, you'll have to open it up to do so.

Video from VoltLog on the subject:

Thanks, great link.

Does anyone also know whether this HP 3478A can measure voltage and current at the same time?