Datron 1281/1271 Cal-RAM backup - how

[pelule]

In my Datron 1281 (8.5 digit) bench DMM it seems, some of the electrolytics haved aged and need to be replace. I like to save the CAL-RAM content for security before working on (A backup is a good idea anyhow, if the battery drops).
Does anyone know how to do (is there maybe a GPIB dump possible like for the HP3458A)?
For sure it is possible to wire an LOGIC ANALYZER to the RAM and read out to file. But this is a risky job and my damage the content by accident. Thus I like to use another more secure method.

Any hint is welcome.

[ManateeMafia]

The Datron 4920 Users handbook shows a DUMP? command that appears to step through the cal ram data. I do not know if this applies to the 1281 or not.

I was able to change the battery in my 4920 using a battery operated soldering iron while the meter was turned on. I do not know if this was the best method but it was the only option I had.
The iron was bought locally for $20US and I have used it on a couple "hot" replacements without issues.

[acbern]

Option also is to remove the board, solder wires connetced to a PSU with 3V over a resistor (current limiter) to the battery traces and replace the battery while baord is out of the unit. I prefer this method because it avoids soldering in a running unit, very easy to cause a short and then the damage may be major.

[quarks]

As acbern points out it is dangerous to solder in mains powered and turned on gear.
But if you are careful and have good access, I think the ManateeMafia way would be ok for me.

[pelule]

The Datron 4920 Users handbook shows a DUMP? command that appears to step through the cal ram data. I do not know if this applies to the 1281 or not.

I was able to change the battery in my 4920 using a battery operated soldering iron while the meter was turned on. I do not know if this was the best method but it was the only option I had.
The iron was bought locally for $20US and I have used it on a couple "hot" replacements without issues.

The DUMP? command is not listed for the 1271/81 but may operate like for the 4920.
This DUMP? query command returns some specific calibration values (floating point) and does not dump the complete memory content.
There may a hidden option of that command to dump complete RAM.

[Mickle T.]

All of the GPIB keywords are stored in the U183-184 ROMs.

[dom0]

Any ESD-safe iron works fine on live stuff powered by an earth-referenced supply.

[radix]

I don't quite get you... How can a soldering iron with an earthed tip be good for working on live stuff powered by an earth referenced PSU? Could you please explain it to me?

Thank you.

[pelule]

to push the discussion back to the item I like to ask tips for:
I like to dump the CAL-RAM content for backup and safety. I do NOT need to replace the battery. Battery is in good shape. I need to check and maybe replace some caps on the board.

[dom0]

I don't quite get you... How can a soldering iron with an earthed tip be good for working on live stuff powered by an earth referenced PSU? Could you please explain it to me?

ESD safe irons have a tip connected to earth by a high resistance (usually 1 or 10 M?). They're not earthed directly, which isn't ESD safe (provokes large discharge currents => parts get damaged).

[radix]

Huh. I thought it was supposed to be grounded. My Ersa iCON nano also has an earthed tip and so do the school Weller magnastats.

It looks like you should check before attempting to solder live parts...

[pelule]

(fyi: I posted also in volt-nuts)
Next chapter of that probably never ending story...

As already mentioned some time ago in this post, I like to backup the Datron 1281 CAL RAM data. Mine need to be refurbished (caps replacement, case cleaning...)
The 1281 is still quite good in cal (~3ppm difference to my 3458A which had last cal 2014/OCT), which I don't want to risk.
In any case this migh a helful knowledge for all of us.

I am lucky having another 1281 "for part" without a Display- and DC-Assembly but a working Digital Board.
I dumped the ROM to have a deep look into the GPIB commands and searched for potential undocumented existing
(like it was done for the 3458A already).

I found following, in the service and user manual not documented, potential commands (?):
RAM = may a RAM command, seems to be the best chance
PRIM = may a subfunction of RAM for primary RAM
SECN = may a subfunction of RAM for secondary RAM

IPZ = no glue yet

YEUK = command to set something, no glue yet about function
YEUK? = query of the YEUK command

CALISS? = seems to be a qery for calibration purpose

To (hopefully) save some of the allways limited private time, I would like to aks, if some of you have seen that commands (?) and has details on them. They may used at other Daltron tools also...

Next I will start with the debugging of the unknown remaining commands on processor board level.

Thanks for help already in advance.
BR
PeLuLe

PS: I just have uploaded the complete 1281 service manual to KO4BB as the company, holding the copywriigth has closed business and has given all doc and rights the "Internet Archive".

[TiN]

Thanks for info and manuals, that's very useful for one experiment currently in progress.
 

[pelule]

Based on "rigrunner" great findings I could create a Datron 1281/1271 NVRAM download tool via the GPIB-Interface.
   [https://www.eevblog.com/forum/repair/datron-1271-repair/msg1307031/#msg1307031]
Thus no need to open the meter to backup the complete 8k NVRAM.
The download I verified against the memory dump using a 68k In-Circuit emulator.

The PDF shows the NVRAM adressing and organisation on the 1271 & 1281 (as known so far).

It is a EZGPIB-Script, creating a file in the HexIntel format, named "NVRAM1281.HEX".
That file can be used for example to directly program the CAL data into a 8k FRAM.
  Note: due to limitations of EZGPIB the HEX-File has 2 times #13/#10 at the end of each line. But the files are useable.

For documentation purpose I have added also that original dump files (DUMP_NVRAM [org].ZIP) and the download of my 1281 (NVRAM1281.ZIP):
  DUMP_NVRAM [org].txt = created with 1281/1271 DUMP command
  I68k_NVRAM [org].TXT = created with 1281 and a 68k In Circuit Emulator
  NVRAM1281.HEX = HEX file created with my EZGPIB script.
  NVRAM1281.BIN = Binary file created out of the HEX file with the MiniPro 

/PeLuLe

[ManateeMafia]

PeLuLe,

Great work and thanks for sharing. 
I will get this added to the xDevs article as soon as TiN isn't too lazy shy busy to do it. 

[leighcorrigall]

Hello PeLule,

Were you able to successfully upload the BIN file onto your Datron 1281?

I ask because I am modernizing rigrunner's script so that it runs on python3 and I need confirmation that both "NVRAM1281.BIN" and "DUMP_NVRAM [org].txt" are legitimate. Unfortunately, I cannot run his script on my Linux box because it is obsolete and I have no way to verify my own script without comparing it with others.

Regards.