Datron 1281 Repair/Maintenance

[leighcorrigall]

...

After the removal of the DC board, I realized that there are at least two Mini Grip mounts that are broken because of ageing (attached). By the way, the through-hole standoffs fit an 11 mm diameter hole for anyone interested. Does anyone have information on these parts? I plan to order replacements and spares.

The only information I can find is from the Chassis Assembly (see Drawing No. 480737) part list:
Datron part number: 450580-1
Description: plastic standoff

Maybe it is time to fabricate replacements...

EDIT:

-- Attached is a representative CAD model of the part in both STP and PAR formats. An update was made to the original ID (0.250 inch to 0.0252 inch) and also includes a chamfer (45 °) so that the Nylatch fastener assembly can be removed easily.

-- Before installing the standoff onto the board, make sure that the plunger and grommet assembly fits loosely into the standoff hole. Otherwise, there could be alignment issues that will cause damage to the fastener assembly. You have been warned.

-- If you plan on replacing all 21 standoffs like I do, remove all analog boards, THEN remove only the DC standoffs. Removal of a single side at a time will make it easier to identify which of the standoff holes are for the boards. Otherwise, review each board hole position from the illustration (options.png) from post #1.

[leighcorrigall]

...

Datron part number: 450580-1
Description: plastic standoff

Maybe it is time to fabricate replacements.

I have reproduced standoffs for testing purposes. They were quickly made from the attached CAD model. I plan on improving the standoff resolution for the next print.

If anyone is interested in replacement standoffs, please let me know and I can ship them for the base cost. These parts are needed in combination with the Nylatch fasteners that secure many of the PCBs to the frame.

EDIT: The attached images show a comparison between the broken original pieces and the newly fabricated prototypes.

[leighcorrigall]

Calibration data of the Datron 1281 can be accessed and reprogrammed via GPIB.

The attached Python 3.7 scripts save the 'DUMP?' data (confirmed) for backup purposes:

1) The nvram_raw_dump.py script is based on rigrunner's original that was modified by TheSteve to correct for the region order (Python 2.7, https://www.eevblog.com/forum/repair/datron-1271-repair/msg3293128/#msg3293128). This script saves the raw "DUMP?" output from the instrument to a file. The raw file can be converted with the following Linux command line suggested by chekhov:

Code: [Select]

cat <file_name>.raw | sed 's/\(^....\)\| ..//g' | xxd -l 16384 -p -r > <file_name>.bin
2)  The modernized nvram_bin_dump.py script saves the "DUMP?" output from the instrument as a binary.

Both approaches listed above have identical outputs (attached). Binary files match and can be examined with the following command lines:

Code: [Select]

diff -du <file_name_1>.bin <file_name_2>.bin

Code: [Select]

xxd <file_name>.bin
Once your binary file is verified, it can be programmed onto FM1808 as described by the xDevs.com article: https://xdevs.com/fix/d1281/#adapters

If anyone would like to share your bin and raw output files, please do so.

Special thanks to the following people for helping me achieve this outcome:

  rigrunner, TheSteve, ManateeMafia, chekhov, TiN

[leighcorrigall]

Using ibtest, the Datron returns the following line when sending it the data string:

write:

Code: [Select]

EXT_DUE?
read:

Code: [Select]

'"150812  "
'
According to the user's handbook, the description is as follows:

The value returned is the date most recently entered either as a parameter of EXITCAL, or when calibration mode exited from the front panel.

Does anyone recognize this as a date? It might confirm the last calibration for me.

[alm]

In the EU, 15-08-12 would stand for 2012-08-15 (unambiguous ISO 8601 notation).

[dietert1]

And DUE should be "calibration due", not last calibration.

[leighcorrigall]

...

 I plan on improving the standoff resolution for the next print.

...

Attached is the second revision of the Datron PCB standoffs (P/N: 450580) fabricated with a Figure 4 by 3D Systems. I made 84. CAD files have been provided above. The material is called "Pro BLK 10".

[leighcorrigall]

...

2)  The modernized nvram_bin_dump.py script saves the "DUMP?" output from the instrument as a binary.

...

Both the Python 3 nvram_raw_dump.py and nvram_raw_dump.py scripts (provided above) produce identical outputs to the previous nvram-2.out.py Python 2 script:

https://www.eevblog.com/forum/repair/datron-1271-repair/msg3293128/#msg3293128

I verified these scripts by interfacing the Datron with an Agilent E5810A (thank you, pipelie!) and using the vxi11 library instead of the Gpib library which no longer can be installed easily with pip on Python 2. 

Code: [Select]

pi@raspberrypi:~/Downloads/backup $ sudo python2 nvram-2.out.py
Reading nvram from Datron Instruments 1281 to 020206-4.X.nvram
Dumping PRIM to "020206-4.PRIM.nvram"
PRIM done.           
Dumping IPZ to "020206-4.IPZ.nvram"
IPZ done.           
Dumping SECN to "020206-4.SECN.nvram"
SECN done.           
Creating 020206-4.nvram.bin
Finished.
pi@raspberrypi:~/Downloads/backup $ diff -du 020206-4.nvram.bin 2021.12.15.020206-4.nvram.bin
pi@raspberrypi:~/Downloads/backup $
Now that the calibration data backup has been made, I will have no issue handling the Datron digital board. 

Pretty good considering that I had no idea how to use a Raspberry Pi or Python last week. 

Thank you, everyone. 

[syau]

Now that the calibration data backup has been made, I will have no issue handling the Datron digital board. 

Pretty good considering that I had no idea how to use a Raspberry Pi or Python last week. 

Thank you, everyone. 

Feasible to share the dump as I want to restore it on my lost calibration 1281 for some testing.

[leighcorrigall]

Now that the calibration data backup has been made, I will have no issue handling the Datron digital board. 

Pretty good considering that I had no idea how to use a Raspberry Pi or Python last week. 

Thank you, everyone. 

Feasible to share the dump as I want to restore it on my lost calibration 1281 for some testing.

I shared the dumps and scripts already. See post #27:

https://www.eevblog.com/forum/metrology/datron-1281-repairmaintenance/msg3876473/#msg3876473

[syau]

I shared the dumps and scripts already. See post #27:

https://www.eevblog.com/forum/metrology/datron-1281-repairmaintenance/msg3876473/#msg3876473

Missed that attachment, thanks.

[leighcorrigall]

Just my luck. More things to consider...

On removal of the AC board, I found problems with the AC board standoffs. Someone applied too much torque while fastening them to the board and they were damaged or have separated from the metal frame. It will be difficult to fix the press-fit standoffs. If you decide to remove the AC board, wiggle the press-fit standoffs to see if they separate from the board -- they should stay secure.

The male-female threaded insulated standoffs have the following dimensions:

Nylon dowel:
length: 15.9 mm [5/8"]
diameter: 8.1 mm [5/16"]

Brass threads (male and female):
thread type: M3, 0.5 mm pitch
thread length: 6.3 mm [1/4"]

[volvo_nut_v70]

You can replicate them using Delrin rod, it will tap easily and hold a thread like aluminum. A friend of mine who is a machinist made some up for me. Easiest is to drill both ends, tap to 3mm threads and use a M3 screw body for the threaded end.

[volvo_nut_v70]

You do realize that having bought the 1281 (Congratulations) you are now on a slippery slope and starting to slide!  Datron Wavetek calibrator next    Many of us are past redemption now..

This may help you in the future, my present revision of replacement capacitors and other bits for the Datron Wavetek equipment

[leighcorrigall]

After dumping the calibration data to a binary file with the Python scripts provided above, it is possible to completely update the SRAM (static RAM) system with a preprogrammed FRAM (ferroelectric RAM).

Original SRAM assembly:
The calibration data, among other information, is stored on U106 (e.g., Sharp LH5164D-10L). A 3.6 V lithium-ion battery sustains the memory of U106 while powered OFF. My battery is from 'JUN06', which is old. The battery reads 3.7 V. If you prefer this storage approach, then make note of the battery replacement procedure (Section 4.3 of the Service Manual) so that you can maintain your calibration constants.

FRAM assembly:
Fortunately for me, there have been great people working on this challenge and all I had to do was put the pieces together. I selected the following parts for my adapter board:
CD74HC00M96 (TI, IC GATE NAND 4CH 2-INP 14SOIC)
FM1808-70-P (RAMTRON, IC MEM 256kb 32kx8 parallel 28-DIP)
C0603C104K9RAC7867 (KAMET, CAP CER 0.1UF 6.3V X7R 0603)
CRCW060310K0FKEAHP (VISHAY-DALE, RES SMD 10K OHM 1% 1/3W 0603)
310-87-114-41-001101 (PRECI-DIP, CONN SOCKET 14POS 0.1 GOLD PCB)
342-10-114-00-591000 (MILL-MAX, CONN HDR DIP POST 14POS GOLD)

xDevs.com also has a variation: https://xdevs.com/fix/d1281/#adapters

Installation:
1) The binary file for the FRAM is uploaded with an EPROM programmer. My GQ USB Universal Programmer (R 7.29) does not support the FM1808. Instead, I selected the DS1230 as instructed by TheSteve. My binary file was also 'cleaned' so that only the serial number and calibration constants remained. EDIT: Attached are the NVRAM and FRAM binaries so that you may perform a comparison.
2) When you are certain that you have correctly created a backup, cut the battery lead while the instrument is OFF.
3) Remove the U106 chip with proper tooling.
4) Install the FRAM and the adapter into the pre-existing socket.

When the instrument is turned ON again, you should know right away whether or not the operation was successful. No error messages should appear and you should be able to check your stored serial number (Status -> Config -> Ser#).

[leighcorrigall]

So far, I have replaced all of the aluminum capacitors of Datron 1281. The greatest challenge was with the digital board and the DC board because of the rear removal process and the floating capacitors in the pre-amplifier section (C307, C308, C312, and C313), respectively. If you are going to replace the capacitors at the DC board pre-amplifier section, be prepared to replace the components that the capacitor leads are connected to. This will make it much easier to disassemble and then install onto the board.

C312 and C313 are both connected to Q203? (Linear Systems current regulating diode, J500).

C308 is connected to Q307 (Siliconix N-Channel MOSFET Transistor, VN10LM) and R314 (Holsworthy metal foil resistor: 10 kΩ, 1 %, 50 ppm, 0.12 W). I suggest removing M301 for more accessibility.

C307 is connected to Q308 (VN10LM).

Another challenge was that the DC board had damaged traces caused by the previous owners. Not sure who to blame, but luckily the rework was possible. I would like to point out that, in most cases, a square hole represents a positive termination and a round hole represents a negative termination for the aluminum capacitors.

After replacing the capacitors, I attempted to run the internal calibration procedure (with CAL Switch enabled, Cal -> Ext -> Quit -> Trig). Error 2582 and 2602 occurred and point to the Current Assembly board. Apparently, the true zero checks of the 100 µA (error 2602, P091, 0.0114 µA) and 1 mA (error 2582, P089, 0.000114 mA) range are out of tolerance. Both are out by exactly the same magnitude, which makes me suspect that the problems are related.

[leighcorrigall]

Attached is the latest firmware (version 3.12) from 1996 that was loaded on U103 and U104 using AM27010-150DC EPROMS. Enjoy!

[leighcorrigall]

...

When I got back to my hotel, I foolishly left the instrument running for several hours to warm up so that I could test it when I got back later that evening. After learning more about the functionality of the instrument in the hotel, I pushed a few buttons and the display information scrambled. No smoke or bad smells, although concerning. The unit was still responsive in that I could somewhat understand what was going on from some of the fragmented information presented and I knew that the unit could switch into various modes. At this point, I turned the instrument off not knowing if it would ever come back. Fortunately, the unit functioned properly the next morning. 

...

The scrambled screen seems to occur at random. After I replaced the capacitors on the digital assembly, I noticed that the problem worsened. I decided to reseat U110 (20L8), U111 (10L8) and U107 (10L8). This seemed to have corrected the problem. I suspect that the terminal release button in the back knocks the U110 when removing the PCB and may have caused problems with the socketed terminations.

[leighcorrigall]

...

I attempted to run the internal calibration procedure (with CAL Switch enabled, Cal -> Ext -> Quit -> Trig). Error 2582 and 2602 occurred and point to the Current Assembly board. Apparently, the true zero checks of the 100 µA (error 2602, P091, 0.0114 µA) and 1 mA (error 2582, P089, 0.000114 mA) range are out of tolerance. Both are out by exactly the same magnitude, which makes me suspect that the problems are related.

Turns out that the ranges needed to be zeroed. I did this with a calibrated Keithley 238 operating at 0.0000 nA with triaxial test leads connected to the Datron 1281 inputs. Luckily, I did not need specialized calibration equipment to perform the correction. I was convinced for a while that the instrument needed component replacements.

Steps:

1) Set DCI to 100 μA or 1 mA with maximum resolution. Enable calibration with the key switch. Source zero amps with an instrument such as an SMU below the measuring capability of the Datron.
2) Cal -> Ext -> Caltrig (repeat for all effected ranges)
3) Cal -> Self -> Corrections ON -> Trig ... (COMPLETE) 
3) Test -> Full ... (PASSED) 

Note: If the instrument is experiencing issues, the display will read 'SELF CAL. XXX ##:' followed by '?' or '??' during self calibration. When the instrument finally gives up, it will provide a list of associated errors. These are likely errors that can be calibrated out such as in my case.

[TiN]

I don't quite get why need 238 connected to meter. 238 might have offset and that would be adding error to your zero calibration. Just leave posts open and do a zero calibration without anything external. Similar to having just a short for DCV/ACV zero calibration.

[mendip_discovery]

I don't quite get why need 238 connected to meter. 238 might have offset and that would be adding error to your zero calibration. Just leave posts open and do a zero calibration without anything external. Similar to having just a short for DCV/ACV zero calibration.

It is all I would do in the lab to get a zero reading for current ranges.

[leighcorrigall]

I don't quite get why need 238 connected to meter. 238 might have offset and that would be adding error to your zero calibration. Just leave posts open and do a zero calibration without anything external. Similar to having just a short for DCV/ACV zero calibration.

Fair enough. Leaving the input terminals open should improve results if the Datron had the sensitivity. I will leave the inputs open the next time I calibrate the zero.

I sourced 'zero' current on the 1.0000 nA range of the Keithley 238 knowing that the maximum offset for the Keithley is ±450 fA. This offset is much lower than the measuring capabilities of the Datron 1281:

--> ±100 pA sensitivity for the 100 µA range (0.0000 µA)
--> ±1 nA sensitivity for the 1 mA range (0.000000 mA)

[leighcorrigall]

Members have commented about my unit and its unusual features. Here are a few that I am aware of so far ...

The more time I spend working on this Datron 1281, the more I am impressed by its subtle features.

While asking about the difference between Datron's definition of 'full-scale' (FS) and 'full-range' (FR) on xDevs IRC channel, I found out that the earlier Datron branded models are capable of over-ranging (i.e., full-scale) by twice the full-range. Attached are some examples. I tested all ranges with the exception of 1 kV and 1 A, which I assume do not have this over-range feature. 

[TheSteve]

Members have commented about my unit and its unusual features. Here are a few that I am aware of so far ...

The more time I spend working on this Datron 1281, the more I am impressed by its subtle features.

While asking about the difference between Datron's definition of 'full-scale' (FS) and 'full-range' (FR) on xDevs IRC channel, I found out that the earlier Datron branded models are capable of over-ranging (i.e., full-scale) by twice the full-range. Attached are some examples. I tested all ranges with the exception of 1 kV and 1 A, which I assume do not have this over-range feature. 

All versions(Datron/Wavetek) will do twice full scale. The newest firmware(3.12) does seem to limit it to full scale less one count though.

[Mickle T.]

All of Datron/Wavetek 1271/1281 can do 2.35*Full Range, but only in raw mode without any calibration constants applying.