HP 3458 DVM

Brooke Clarke 2009


Reading Calibration Memory
Voltage References


During my career as an engineer I specified this meter into automatic test systems and wrote code to control them.  The key feature is that they are very accurate.  For example when the definition of the Volt changed we had some instruments with a sticker saying that they measured the new Volt.  When comparing those with the no sticker meters the difference was the difference in the Volt definition.  Quite impressive.

HP Journal for April 1989 - describes the new developments.


The manual does not have the details necessary to troubleshoot down to the component level.  They use board level replacement to fix problems.

This one came from eBay and was sold untested and marked "Strapped for 220 VAC".  It's a very simple thing (rear panel switches) to set it for 120 VAC.  But on power up there is a single beep, the display shows "testing RAM" and all the icons and pixels are on, then quickly changes to ISOLATOR DTACK and locks up there.  Pressing Blue and or Error either at the same time or in sequence does nothing.  The error message is associated with the A5 Outguard Controller board. 

Pressing Blue then Clear or Blue + Clear has no effect on the error message.
Disconnecting and reconnecting all the electrical and FO joints had no effect.
There is a smell like hot phenolic but so far haven't found where it's coming from.

HP 3458A Outguard
                    Controller A5

ICs on A5

U100 is a 68HC000

U110 is a 40 pin UV erasable EPROM marked:
03458-88887, Check Sub = B26A, DS   8061

U140 is a 20 pin IC marked:
03458-88838, SLRW    FN, Check Sum = 2F48   8063

U121, U122 are Dallas Semi DS1230Y-150 Nonvolatile SRAMs (date code 9746H)

U132 is a Dallas Semi DS1220Y-150 Nonvolatile SRAM (9751D)

The three Dallas Nonvolatile SRAMs are all a couple of years past their 10 year lift.  The internal batteries may be dead!
I've heard the batteries should be good for another few years.  If they were bad there might be an error message about the SRAM checksum.
HP 3458A Inguard Power
                    Supply 66504B
A4 Inguard Power Supply 03458-66504B

The diodes are 1N5365B.  What has shorted out to cause CR9,  CR11 & CR12 to die?  These are 5W 40 V Zeners.

Why is CR10 still OK?

There is a connection between the Zener diodes and the 5 pin header nearby.  So the problem may be on one of the boards that's receiving the 40 Volts.  Maybe a bad cap?

A new A4 board is on order with a 33 day  lead time. 29 Jly 09 + 6 wks = early Sep 09.

Working on  schematic.

This may be what happens when 220 VAC is applied when the rear panel straps are set for 120 VAC?
Partial PCB Layout to get schematic
                    3458A A4 Inguard power Supply layout 03458-66504
P1 connects to the transformer secondary.  P1-1 and P1-3 supply the +18 V and -18 V half wave rectifiers with the center tap to P1-2.   Zener CR12 has it's anode connected to P1-3 and it's cathode to CR11 anode.  CR11 cathode to Gnd screw 1.

In a like manner CR09 cathode connects to P1-1, CR09 anode to CR10 cathode, CR10 anode to Gnd screw 1.  So the Zeners are input over voltage protection.
                    3458-66504 A4 Inguard p.s. partial schematic

T1 Power Transformer

Measured with the A4 board removed, i.e. no load.
VAC                                                     Ohms
Pin #

J1 P1

HP 3458A Bottom Inside A4 removed

HP 3458A Bottom

T1  Transformer in upper left.

A6 Below transformer is Outguard power supply.

A4 Central rectangular box is where the Inguard power supply sits.  The red connector goes to the transformer.

A2 AC Circuitry 66502E in the upper right.

A3 A/D Converter & Inguard logic 66503 in the lower right.

HP 3458A Power
                    Transformer 9100-4715

There does not seem to be any troubleshooting information ( VAC or Ohms readings for the transformer nor is there any removal or installation info.

I'd prefer to not completely disassemble the DVM to change the power supply.

31 July 2009 after: replacing T1

With new transformer
Pin # VAC

Inguard p.s. voltages with new transformer:

+ 5:  +5.0
+18: +18.8 (spec: 16.2 to 19.8)
 -18:  -23    (spec: -16.2 to -19.9) <****OUT***
HP3458A Top Open

The Outguard assemblies are on the right and include the power transformer and below it the outguard power supply and on the other side the A5 controller.

The outguard assemblies connect to the inguard assemblies (on the left) mainly via fiber optic cable pairs.

The central hole is for the inguard power supply.

A1 DC circuitry
A9 DC Reference
A10 Front Rear Switch

A5 Controller
1 Aug 2009 - Installed new In guard power supply.  The voltages are now:  5.00, +18.5 and -18.5.
But the same error message.


My board is -3458-66505 Rev C  and is the non option 001 version.  The option 1 board would be 03458-66515.  Option 001 is extended reading memory and probably consists of filling positions U122, U123, U124, U125 with RAM chips and relocating JM600 (just a guess, not yet analyzed).  The Outguard Power Supply board (under bottom cover) shows the two +5 VDC test points to be right in the middle of their allowed range.  The +15 VDC test point (P3 red wire) reads 14.0 VDC but there doesn't seem to be a spec for it.

Option 002 is marked on the rear panel label.  That's the high stability Voltage reference (4 ppm/year).
I have on a bookshelf somewhere the Waveform Analysis Library (03458-80002).  The 3458 can work like a sampling scope but the data comes out in a strange (interleaved) pattern and needs to be put back into time order in order to get a "scope" like display on your computer.

Reading Calibration Memory

There are some memory chips that have an internal backup battery and some instruments are getting old enough that the battery is going dead causing the loss of calibration data.
Thanks to the work of Poul-Henning Kamp there's a way to read out the data from these chips.

All you have to do is enter the commands
	MREAD 393216
	MREAD 393218
	MREAD 393220
	MREAD 397308
	MREAD 397310

and save the results.

But that's 2048 MREAD commands, so having a program to do it
would be a lot easier...
and here is some sample data: HP3458Sample.txt


These are patents that may be related to the HP 3458A.
4357600 Multislope converter and conversion technique,  James Ressmeyer, Joe E. Marriott, Lawrence T. Jones (Hewlett Packard), Nov 2, 1982, 341/129

4766401 Coaxial switching system with switched shields and crosstalk suppression, David P. Kjosness, Joe E. Marriott (Hewlett Packard), Aug 23, 1988, 333/12; 333/262; 335/5

4951053 Method and apparatus for switching currents into the summing node of an Integrating Analog-Digital Converter, Lawrence A. DesJardin, Wayne C. Goeke (Hewlett Packard), Aug 21, 1990, 341/136; 341/135; 341/155; 341/172

5200752 Integrating analog to digital converter run-up method and system, Wayne C. Goeke (Hewlett Packard), Apr 6, 1993, 341/168; 341/166

5117227 Continuously integrating high-resolution analog-to-digital converter, Wayne C. Goeke (Hewlett Packard), May 26, 1992, 341/166; 341/156

5148171 Multislope continuously integrating analog to digital converter, Leon Blumberg, Hewlett-Packard Company, Sep 15, 1992, 341/168, 341/166

5689260 Analog-to-digital converter using scaled signal to initialize coarse conversion circuit, David Gerard Vallancourt, Lucent Technologies Inc., Nov 18, 1997, 341/156, 341/158


This account provided by Dr. Frank and is provided with his authorization.  First appeared on the Volts Nuts list server.
I also picked one up, a mixed one, ie old analogue PCB from the 90's and a younger processor board from 2001 (perhaps replaced due to SRAM battery discharge). Cost me about 3k instead of of 8k new, and its working perfectly - but stable environmental temperature conditions are required, that's the weak point of the design.

Maybe its an old design, but currently, no other DMM or calibrator can beat it essentially in certain parameters.

It has got the best (differential) linearity, over Keithley 2002, Fluke 8508A, Datron 1281, Fluke 57xx and even the Primary Ratio standard 720A! Only the JJ array can test its linearity!

OK, the 3458A's internal references are not that stable, but it is not intended as a secondary volt or ohm standard.

For that you need additionally something like a 732B and a SR 104, or the quantum standards, respectively.
But all others of the above mentioned, newer DMMs are not much better.

For DCV, the 3458A obviously has been designed for a very broad temperature range of 0..55C (military use??), which gives an internal temp of at least up to 80C in a rack mount.  Placing its internal volt and ohm standards in a lower and more stable environment would have been better, but then, it could not have been a DMM-in-one-box.

So the internal LTZ1000A reference has to be running  on 90C.
If powered constantly, this gives at least 20 times higher drift rates over time compared to a Fluke 7000A, which is running on 45C.
Other DMM are specified for meteorological temp. range and have certainly slightly better drift rates (two times).

I have set (pimped) the LTZ to about 55C for lower drift.

The HV divider cannot be corrected for power dissipation effects, so the 1000V range is quite mediocre.
I have built my own 100:1 Hammond type divider (~ 752A) to get around 1ppm for 1000V.

The ohm ranges obviously is its weakest mode.
It relies on an elder hermetically sealed Vishay resistor, with high time and temp. drift, and additionally the resistor is exposed to the strong internal temperature variations.

Today, by using a selected VHP202Z resistor, one might improve time drift to <1ppm/year and stability (with respect to temperature) to < 0.2ppm over the complete "meteorological" ambient temp range.

Additionally, its ohms range resistors are very sensitive to temperature changes.

But it is possible by using it in absolutely stable amb. temp. conditions (+/- 0.2K), to make 10k Ohm measurements / transfers on sub ppm stability level.

Currently, I'm working on external 10k standard resistors; but still in discussion with Vishay.
Report will follow.

ACV is also unparalleled by other DMMs, due to its (patented?) digitizing algorithms, and this can be further improved by Swerleins Algorithm. So I think, only Flukes AC standard 792A is "better", if using standard electronics.

So my advice, get one used 3458A, it's simply a nice and ultra precise box, and build yourself some standards which you would need also if you got a newer DMM.

Btw.: A good, absolute calibration is nearly impossible to acquire for us amateurs. Even Fluke and Agilent obviously offer 2nd grade calibrations only.


Voltage References

The Linear Technology LTZ1000 is the heart of many voltage references see LT app note 86 appendix I Fig 12.
LTZ1000 chips: eBay seller polida 2088


HP Journal - April 1989 the 3458A is the Cover Feature
K04BB - HP 3458A Precision Digital Multimeter - two different HP calibration options

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