Contents

• Intro
• Disclaimer
• Manuals and service information
• Restoration of xDevs Datron/Wavetek 4910 DC standard
• Using Datron 4910 for external calibration transfers
• Datron 4912 Teardown
  • Power Supply Assembly
  • Main Board Assembly
  • Cell PCB Assembly
• Summary and conclusion

Intro

Datron 4910 series include primary 4-cell SSR DC voltage standard and stripped 4911 (w/o 1V/1.018V divider) and 4912 (single cell only). These 4910 DC reference standards were among the first ones to work as first replacements to the fragile and sensitive Weston cells. It provides stable 10 DC Voltage output with a stability of better than 1 µV/V per year. The unit features internal battery pack out of 18 6V 2Ah lead-acid battery modules with long life and is great option for transfer applications and metrology use. Accuracy resolution of this standard is between 0.1 µV/V – 0.2 µV/V. The operating temperature range is specified at 0°C to +40°C. Temperature coefficient of a 10 V averaged output and cell is 0.05 µV/V/°C.

Datron 4910 with it’s 4 separate isolated cells, each of which have own reference is a direct competition to Fluke’s 734A reference system, which consist of four more modern Fluke 732B modules. Since 4910 was designed earlier prior to Fluke acquired company’s assets, it’s likely that 734A was developed after seeing how powerful and useful is the multi-cell output like implemented in Datron 4910. Fluke used their own Motorola-designed reference amplifier (SZA263) that found itself in many of Fluke’s products from DMM’s, calibrators, and voltage references.

Datron went a different route here. They chose a commercially available voltage reference, the Linear LTZ1000. This LTZ1000 chip is considered as the best available buried zener reference by many engineers and the specifications of the 4910 series also show how competitive it is. Datron/Wavetek references also made it into their other high end test equipment. They can be found in the 1271/1281 DMM’s, the 4920 AVMS, and in their multifunction calibrators like the 4708 and later Fluke’s own 8508A DMM. It was a departure from Datron’s older original designs where they chose several zener diodes and matched their tempco to provide a reference that was stable with both time and temperature.

Second Datron’s major departure in design hides in way it scale output voltages to nominal 10 V and 1 V/1.018 V. Common reference zener DC standards utilize expensive high-end resistance elements in hermetic packages to amplify/divider voltages to desired levels, relying on long-term stability and very low temperature coefficients of such resistors to deliver good performance. While failures of such resistors are not common this approach does significantly increase cost of implementation and production of DC voltage standards. Datron 4910 instead utilize digital method to amplify/divide voltages with low frequency PWM with help of timing circuits, moderately good scaling resistors and extensive output filtering. Somewhat similar method is also used in other products such as Fluke 5700A, newer Fluke 5720A calibrators, Fluke 5790A AC/DC voltmeter and Valhalla 2720GS DC calibrator.

This time we will take a look on rare Model 4912, which is a member of the 4910 family series of voltage references from Datron/Wavetek. They are of a similar size and weight to the Fluke 732A and were in direct competition. Special Datron 4912 differs from the 4910/4911 due to limited single “cell” output. Just like fully featured Datron 4910 this special Datron 4912 also includes a low impedance 4-wire output plus divided outputs at 1V and 1.018V. Unlike 4912 other two models include all four “cell” outputs with the capability to average them together, or even build higher voltage outputs since each output can be fully isolated.

Specification	Fluke 732A	Fluke 732B	Fluke 732C	Fluke 734A or 734C	Datron 4910	Datron 4911	Datron 4912
Output voltage, DC	1V, 1.018V, 10V	1.018V, 10V	0.1V, 1V, 10V	4 × 732B or 732C	4 × 10V, 10V average, 1.018 V, 1.000 V, buffered 4-wire	4 × 10V, 10V average	1 × 10V, 1.018V, 1.000V, buffered 4-wire
Stability (30 day, 10V)	±0.5 ppm	±0.3 ppm		<±0.3 ppm	±0.3 ppm	±0.3 ppm	±0.3 ppm
Stability (1y, 10V)	±6 ppm	±2 ppm		<±2 ppm	±1 ppm	±1 ppm	±1.5 ppm
Temperature coefficient, ppm	±0.05 ppm/°C	±0.04 ppm		±0.04 ppm	<±0.05 ppm/°C
Adjustment range	50µV, <0.05ppm	None			PWMDAC switches
Reference design solution	Motorola SZA263	LTFLU-1			up to 4 x Linear LTZ1000ACH
Max load current	12 mA	12 mA			15 mA for buffer only
Output noise	<1 µVRMS, 0.1-10Hz	<0.6 µVRMS, 0.1-10Hz			<0.4 µVRMS, 0.1-2 Hz
Construction type	Rugged half-rack module	Rugged ¼-rack module		Full-width 19” rack frame	Rugged half-rack module
Active thermal compensation	Yes, +45° C oven assembly				LTZ1000 internal oven
Temperature sensor for monitoring	Yes				No
Operation range, ambient	+0…+40 °C
Power requirements	100,120,220,240VAC or 24-40VDC	100,120,220,240VAC or 12 VDC			100,120,220,240VAC or 10-40 VDC
Backup/offline power supply	Internal ±12V Battery bank, 12 hours life	Internal ±12V Battery bank, 72 hours life			±18V 15pcs battery array, 168 hours life transit mode
Dimensions, weight	603 × 221 × 191 mm, 12.3kg	254 × 206 × 311 mm, 4.8kg			591 × 214 × 182 mm, 20 kg
MSRP	~$2k USD [1984, EOL]	$9k USD [EOL]	$16k USD	$60k USD	$8k+ USD [1990, EOL]

There is no manual currently available for the 4912 so the 4910/4911 manual was used for troubleshooting.

Disclaimer

Redistribution and use of this article or any images or files referenced in it, in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of article must retain the above copyright notice, this list of conditions, link to this page (https://xdevs.com/article/d4910/) and the following disclaimer.
• Redistributions of files in binary form must reproduce the above copyright notice, this list of conditions, link to this page (https://xdevs.com/article/d4910/), and the following disclaimer in the documentation and/or other materials provided with the distribution, for example Readme file.

All information posted here is hosted just for education purposes and provided AS IS. In no event shall the author, xDevs.com site, or Datron/Fluke or any other 3rd party be liable for any special, direct, indirect, or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortuous action, arising out of or in connection with the use or performance of information published here.

If you willing to contribute or have interesting documentation to share regarding pressure measurements or metrology and electronics in general, you can do so by following these simple instructions.

Manuals and service information

Datron 4910/4911 User’s Handbook

Datron 4910/4911 Service manual 1991 w/schematics

Datron 4910/4911 Service manual 1990 w/schematics

Separate pages for Cell schematics, part 1

Separate pages for Cell schematics, part 2

Separate pages for Cell schematics, part 3

Separate pages for Cell schematics, part 4

Separate pages for Clock schematics, part 1

Separate pages for Clock schematics, part 2

Datron application note explaining PWMDAC approach

---

Some additional community-generated files also available to aid understanding of 4910 design, especially LTZ1000CH-zener cell modules.

Service for D4910 by master Lymex

Schematics reverse engineered for zener module

Schematics clone for VHD variant of zener module

Schematics clone for VHD variant of zener module

Gerber file for VHP/VHD zener module

Gerber file for 7-10V PWM module cell

Restoration of xDevs Datron/Wavetek 4910 DC standard

In February 2026 good decade since this article was first drafted up xDevs HQ finally got our very own Model 4910 for lab use. Standard arrived in a poor condition with ruined front terminals and dead batteries. We’ll attempt a full restoration and document the progress in this article. DC reference was acquired from secondary market and came in poor shape due to it’s previous life adventures.

All front binding posts were damaged and heavily discolored by exposure to sun or heat over long duration. These posts aren’t good design in the first place even new. CELL 2 LO and 1.018 V HI terminals are sheared completely off, only leaving useless stub. Every single post base is fractured and discolored badly.

Removing front panel was easy as whole front assembly held by two screws and connected to 4910 mainboard by DIN dual-row interconnects.

Rear side shows few labels with front PCBA part number 400880-2.0 880/025/001, tested on 7/10/1994 by IDH.

Each HI/LO pair output coupled with passive RC network and gas discharge tube to arrest any static from external world. Each binding post making contact to gold-plated PCB pads with gold-plated washer and gold-plated nut.

Removing few nuts revealed some green copper oxide crust that definately warrant full cleaning process with abrasive materials, even before we install new binding posts.

PCB area around LEDs show clearly visible discoloration due to years of heat generated by diodes.

Perhaps I’ll replace those LEDs to something modern and lower power to make it nicer :)

Additional isolation PCB was hiding under front panel electrical PCBA, since binding posts were not equipped with rear insulation washer. Yet another reason to replace these posts to get better insulation from case metal front panel block.

Close-up on original binding posts, manufactured by Cliff Electronic Components, similar to modern TP1 model.

They are somewhat similar to low quality Pomona 3770 terminals but not mechanically identical.

All of these must go, no questions asked here.

Original front panel metal case has cutout indents to prevent post from turning around when mounted on front-panel.

Markings and face labels are on decorative metal plate P/N 450751-4, stuck to metal casting panel with a strip of double-sided adhesive.

So first action was to replace them with something robust and nicer. After few trials and xDevs inventory checks I’ve decided to go with special order bare copper terminals with PTFE insulation washers.

These should do the job nicely and they are well tested for nanovolt-grade signals.

And here’s look with all posts installed for test fit:

Main cell outputs all used longer posts to fit double nuts for extra security for nanovolts.

I’ve also cleaned up rear PCB surface with sandpaper a bit.

Holes were drilled little bigger to fit the PTFE insulation washer from bare copper posts.

Same drilling was done for both face panel and front panel metalwork.

All edges were deburred and cleaned up prior to installing insulators and posts.

All done and ready:

Much cleaner and nicer. I’ve cleaned and reused original gold-plated shorting bars for 4-wire output buffer and guard-case terminals.

Battery cells power pack

To replace old dead accumulators I’ve bought 15 pcs brand new Powersonic PS-621.

I’ve sorted batteries by their voltage and change level into groups, since they are used in 3S arrays with total of 5 arrays.

Here’s finished battery pack after cleaning and batteries replacement. Hopefully it will live well until estimated service four years from now in 2030.

Be sure to check every battery array output for proper polarity and voltage at the output DB connectors. Schematics is the most helpful to identify required pins which are:

• Pack 1, +18 V nominal for Cell 1 = pins J9.1 (BLACK) and J8.1 + J8.2 (RED)
• Pack 2, +18 V nominal for Cell 2 = pins J9.2 (BLACK) and J8.10 + J8.11 (RED)
• Pack 3, +18 V nominal for Cell 3 = pins J9.3 (BLACK) and J8.4 + J8.5 (RED)
• Pack 4, +18 V nominal for Cell 4 = pins J9.4 (BLACK) and J8.13 + J8.14 (RED)
• Pack 5, +18 V nominal for Divider/timing outputs = pins J9.9 (BLACK) and J8.7 + J8.8 (RED)

Motherboard repairs

Next repair step was to check and power regulators and power supply rails on motherboard. Old test equipment commonly develop faults in power filter/regulation circuits causing cascading failures for various functions and modules. To address this I’ve usually replace all electrolytic and tantalum capacitors and carbon resistors and then test each regulator for compliance with specs and noise.

At the back side we can find monster multi-pole switch that selects power path for all battery packs between normal mode and transit mode.

Datron service manual provides us with description of various useful test points and expected voltages on board board. Table 2.2.11 is reproduced below with my own measurements before and after repairs:

Supply	Test points	Specification		Drawing	As received		As repaired
		without battery	with battery		without battery	with battery	without battery	with battery
I+ (1)	TP102 vs TP101	24.5 VDC ±0.5V	20.6 VDC ±0.25V	DC400878 Sheet 1	25.39 V	21.73 V	24.16 V	20.60 V
I+ (2)	TP202 vs TP201	24.5 VDC ±0.5V	20.6 VDC ±0.25V	DC400878 Sheet 2	25.06 V	21.33 V	24.26 V	20.60 V
I+ (3)	TP302 vs TP301	24.5 VDC ±0.5V	20.6 VDC ±0.25V	DC400878 Sheet 3	27.54 V	23.23 V	24.01 V	20.61 V
I+ (4)	TP402 vs TP401	24.5 VDC ±0.5V	20.6 VDC ±0.25V	DC400878 Sheet 4	24.70 V	20.96 V	24.31 V	20.61 V
I+ (5)	TP502 vs TP501	24.5 VDC ±0.5V	20.6 VDC ±0.25V	DC400878 Sheet 5	26.60 V	22.87 V	24.02 V	20.61 V
+12V REG (1)	TP104 vs TP101	12 VDC ±0.6V		DC400878 Sheet 1	12.21 V		12.21 V
+12V REG (2)	TP204 vs TP201	12 VDC ±0.6V		DC400878 Sheet 2	12.19 V		12.19 V
+12V REG (3)	TP304 vs TP301	12 VDC ±0.6V		DC400878 Sheet 3	12.28 V		12.29 V
+12V REG (4)	TP404 vs TP401	12 VDC ±0.6V		DC400878 Sheet 4	12.39 V		12.36 V
+12V REG (5)	TP504 vs TP501	12 VDC ±0.6V		DC400878 Sheet 5	13.56 V	0.3 V	13.47	13.49 V

LTZ1000CH ultra-zener chip is a core heart of the instrument. We have seen these same modules inside of long-scale Datron 1271/1281 DMM , Wavetek 4950 transfer standards and Wavetek 4920M AC voltmeters. Same module was used even in early Fluke 8508A DMMs:

Later 8508A were retrofitted with a simpler LTFLU-1 reference module.

Rear panel powersupply PCBA

Rear metalwork was a bit bent but nothing that hammer couldn’t fix.

Reference Cell LTZ1000CH PWMDAC 10 V modules, DOM 1994

Output buffer and 1V/1.018V divider PWMDAC/timing module, DOM 1994

Repairs summary with bad parts:

First datalog after reassembly:

Sadly we still have some more repairs to do, as the 4910 stopped behaving nicely after initial few days warmup and adjustment to 10 V output on each cell. Cells were connected in averaging mode and here’s the overall collection of samples across 1 week:

To confirm that it’s not a measurement artifact I’ve prepared a chart with all the other zeners in array as well, with historical data going back to January 1, 2026. Almost all standards on this chart were continously monitored and powered since year 2019.

Repairs and more in depth troubleshooting are to be continued.

Using Datron 4910 for external calibration transfers

One of great features that Datron 4910/4911/4912 DC Voltage standards have is transport mode for long battery life. In this transit mode each cell maintain power to LTZ1000 oven and zener circuits, temperature setpoint circuits and health monitoring, while all PWMDACs and digital circuitry is turned off to preserve battery capacity.

With fresh fully charged batteries this mode would let Datron 4910 survive at least 168 hours (7 days) making it suitable for international shipping for long-distance precise ppm voltage transfers. Or it can be used for local transport with plenty of safety margin for battery power. If ambient temperature drops to 0 °C then battery expected life reduced to 100 hours which is still much longer than any other commercial DC voltage standard on the market. In normal mode with fully powered up outputs 4910 maintains battery life at least 8 hours.

In 2020 and later I’ve utilized transit mode and Datron 4910 for external voltage calibration transfer to xDevs lab. Characterized Datron 4910 was tested and measured to obtain “as shipped” dataset. This 4910 was characterized for output noise with LNA setup and oscilloscope to confirm that every output provides stable and low noise output.

Other high-quality 10 V standards were used to verify each 4910 output. This was done with number of methods.

There are multiple ways to calibrate 10 V zener standard, but perhaps most common is substitution measurement with long-scale DMM such as Keysight 3458A or nanovoltmeter like Keithley 2182A or Keysight 34420A.

The substitution measurement can be done in five steps to uncertainty better than 1 ppm with common 8½-digit DMM.

STEP 1: Measure zero offset of the meter. Short cables to DMM at the DUT standard post and measure residual EMF.

STEP 2: Measure known calibrated 10 V standard in positive polarity with long-scale DMM.

STEP 3: Flip cable connections at the known calibrated 10 V standard for negative polarity measurement.

Now calculate the thermal EMF with correction for thermal EMF error offset, to obtain V_REFERENCE value.

STEP 4: Measure unknown device under test 10 V standard in positive polarity with long-scale DMM.

STEP 5: Flip cable connections at the unknown DUT 10 V standard for negative polarity measurement.

Now calculate the thermal EMF with correction for thermal EMF error offset, to obtain V_DUT value. With both values available one now can calculate ratio between the DUT standard and known reference. This method is limited only by stability of references, uncertainty of short-time 15 minute transfer of DMM. With careful setup and repeating this process multiple times it’s possible to perform 10 V calibration to uncertainty around 0.5 µV/V relative to known calibrated 10 V standard.

This process and procedure is also well covered in this article. Temperature was monitoring for the whole duration of transfer experiment. For larger and better uncertainty comparisons can be done with series-opposition method with nanovoltmeter and low-thermal scanner, but that’s outside of this article scope.

Then standard was packed in Pelican iM3075 Storm hard-plastic case and shipped with standard commercial service to calibration laboratory. Each output was measured for number of days and recorded for future reference. Then 4910 was switched to transit mode again and shipped back to xDevs. Once received each output was monitoring against our local zener array that never left the shelf and each cell output was recorded in “as received” dataset. This was compared to previous “as-shipped” dataset to determine any shifts or large discrepancies due to shipping travel and stress.

Temperature datalogger was included in the case to monitor internal environment during the shipping transport. Overall shipment weight was about 48 kg.

Teardown for Datron 4912

This specific Datron 4912 was acquired from a member of the volt-nuts group as being defective, but in good physical shape. The condition in which it was received showed that there was an issue with the batteries/charger and the output was low at approximately 0.5 VDC.

The unit was opened and inspected for obvious issues. Apart from a cable from the battery assembly being disconnected, there was nothing that appeared wrong visually. Time for disassemble and tests.

Battery compartment:

Original batteries were Powersonic PS-618 rated for 6 Volt and 2.0 Amp*hour capacity. These are not available anymore and smaller replacement is PS-621 which are quite different mechanically.

Power Supply Assembly

The power supply is part of the rear cover. It includes the transformer, power supply pcb, an external DC input connector, and a power input module. The power supply pcb has five identical isolated supplies.

It was easier to troubleshoot by comparing outputs of each of the regulators. Two of the regulators had a low input voltage. The circuits were traced out but no issue was found with the parts on the board. It was determined that the ground path in the two circuits was interrupted. The 1N4148 diode in the path on the ground side was removed and tested to be good using a Peak DCA75 on both supplies. A diode from one of the other supplies was removed for comparison and it was discovered that it was a 10V zener. Somehow the diodes were changed and the wrong type was installed. After replacing both diodes, the two supplies sprang to life and all looked well.

Further testing of the 10V output still showed no change in the output level. More troubleshooting was needed.

Main Board Assembly

The main board includes separate circuits for each of the five supplies from the power supply assembly. This too made it easy to test. There is also a circuit to handle an external DC supply with its own regulator. A transit mode switch is also located on the board. The switch is used to select a low power mode for shipping of the reference. The switch protrudes from the rear cover. There are also connectors for up to four cell PCBs. It appears that Datron used the same backplane design for all three models. In the 4912 there are three slots that are not populated.

Comparing the voltages on each of the five circuits, it was found that the 12V was missing from two of three unused supplies. They have probably been defective for a long time but they had no effect on the operation of the single cell. The two supplies still needed to be repaired. The inputs were tested and found to be low. Measuring the resistance across the input path found that the two inputs were shorted to their respective grounds. There is a 1µF/35V tantalum on the inputs. They were removed and confirmed to be shorted. A temporary replacement was installed and the supplies were retested as having good outputs. Again, the reference output was tested but the output was still at 0.5 V. Off to the cell PCB…

Cell PCB Assembly

The cell pcb contains the LTZ1000 daughterboard assembly and also the PWM divider circuits. The divider is broken into a most significant switch and a least significant switch of 16-bits and 8-bits.

The output of the LTZ board measured at ~7.23V between TP105 and TP108. This meant the problem was most likely in the output divider or op-amps. The HI and LO side of the output splits into both the direct output and averaged output. The continuity between the LTZ board LO out and the front panel LO was confirmed as good. The two jumpers connecting the averaged outputs were disconnected for testing purposes.

The LTZ board HI side output goes through two separate op-amps. It was difficult to confirm whether U109 was working as its output was low (0.5V). U111’s output was ~11.5V but the output at the front panel was missing. The resistance between the HI and LO outputs at the front panel measured 7 ohms. It was suspected that more bad capacitors would be found.

All capacitors on the board were measured in circuit but only a couple were across the HI/LO outputs. They were removed and measured. Neither were found to be shorted. Probing around the board searching for shorts proved nothing. The 10V path goes into both dividers. The signal name is 10V(B) according to the schematics. All components in the two dividers were checked but the only issues found were two JFETs (Q204,Q206) had a low resistance across their terminals. They were removed from the pcb one at a time and tested on the DCA75. No readings appeared to be bad. Measuring resistance at the outputs showed that it was now ~130 ohms. The 10V output was then measured with the two transistors removed and it read 9.4V.

Q203,Q205, and Q208 were removed and tested with the DCA75. They also tested as good. It was decided that the transistors in this part of the board would be ordered. Q204 and Q206 have been marked by Datron so most likely they are binned parts. They could also be matched to each other. This will have to be tested if either one is determined to be defective.

Summary and conclusion

Overall this Datron 4910 article and restoration were great fun and rewarding, with addition of four nice 10 V outputs at xDevs.com in-house voltage bank. Total expenses are listed below:

Item	Qty	Cost per unit	Subtotal	Source
Datron 4910 reference, as is	1	$$$$	$$$$	secondary market
PowerSonic PS-621 battery, 6V 2Ah	15	16.431 CAD	246.47 CAD	BBMbattery.ca
LED RGB DIFFUSED T-1 3/4 T/H WP154A4SUREQBFZGW	20	2.039 CAD	40.78 CAD	Digikey 754-1492-ND
CAP ALUM 470 µF 20% 63V RADIAL TH EKY-630ELL471ML20S	10	1.161 CAD	11.61 CAD	Digikey 565-EKY-630ELL471ML20S-ND
CAP ALUM 330 µF 20% 50V RADIAL TH B41896C6337M000	10	1.347 CAD	13.47 CAD	Digikey 495-6043-ND
RES 2 kΩ 5% 2W AXIAL PR02000202001JR500	10	0.345 CAD	3.45 CAD	Digikey 56-PR02000202001JR500CT-ND
CAP TANT 2.2 µF 10% 50V RADIAL TAP225K050SRW	20	0.953 CAD	19.06 CAD	Digikey 478-8970-1-ND
CAP TANT 3.3 µF 20% 50V RADIAL TAP335M050CRW	10	1.152 CAD	11.52 CAD	Digikey 478-TAP335M050CRWCT-ND
CAP ALUM 1000 µF 20% 63V RADIAL UBY1J102MHL1TN	10	2.682 CAD	26.82 CAD	Digikey 493-UBY1J102MHL1TNCT-ND
CAP TANT 10 µF 10% 50V RADIAL TAP106K050CCS	20	1.716 CAD	34.32 CAD	Digikey 478-4172-ND
CAP ALUM 10 µF 20% 100V RADIAL TH REH0611100M100K	10	0.206 CAD	2.06 CAD	Digikey 478-REH0611100M100KCT-ND
MOSFET P-CH 60 V 280 mA TO92-3 ZVP2106A	20	1.257 CAD	25.14 CAD	Digikey ZVP2106A-ND
FUSE BRD MNT 1 A 125VAC/VDC AXIAL 0251001.MXL	10	1.252 CAD	12.52 CAD	Digikey F2313-ND
BUMPER SQU 0.81“L X 0.81“W BLK SJ-5023-BLACK	36	0.431 CAD	15.54 CAD	Digikey SJ-5023-BLACK-ND

Total spent about 463 CAD and 30 hours on random evenings not including the Datron 4910 unit itself. The author would like to express our appreciation to everyone contributed to this project, especially Alex, Todd, Ken Eckert, David, Lymex. Discussion is very welcome thru comment section or at our own IRC chat server: xdevs.com (port 4808, channel: #xDevs.com) or at our own forum.

If you have information and interesting ideas on Datron 4910 hardware modifications not mentioned or listed in this article, feel free to provide them and xDevs can test and add them with next article update. If you have own Datron 4910/4911/4912 in your lab, I’d love to hear about it and showcase your insturment performance here as well.

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