Danfysik / LEM 867 series service manual?

[WallWart]

Hello, I'm looking for a service manual for an old Danfysik (LEM?)  867-700 current transducer.  A few have failed in the lab recently.   Some probing suggests that the output is shorted by a relay when the power is off so I don't think they should be vulnerable to the "current through the bore with no terminator generates damaging voltage" problem of current transformers.   I thought it might be interesting to troubleshoot them a little further but it's been back-burner for a while.   I can find the datasheet easily, but what I really need is for a service manual and a schematic. I thought I saw one in the thread below a few months ago with some internal test waveforms.  Now I can't find it and it's driving me nuts.  I checked the usual haunts without luck - xdevs, and archive.org. Danfysik and LEM aren't talking. Can anyone help me out with some old documents?

Similar thread for the 866 - I see the lymex schematic for the 866 but some probing suggests the 867 is different.
https://www.eevblog.com/forum/metrology/dccts-(ultrastab-for-example)-infos-and-workingdefective-devices-sought/

Datasheet.
https://xdevs.com/doc/LEM/doc/867-700I_Installation_Package.pdf

Thanks.

[Echo88]

Never found any service manuals/schematics for those DCCTs.
Can you share a photo of the pcb so i can compare it to the known Danfysik 866?

[WallWart]

Top and bottom of the Danfysik 867 board.  What jumps out at me is the lack of transformers on the PCB.

[WallWart]

For convenient comparison, here's the Limex schematic and photos. 

[WallWart]

I guess I'm diving down the rabbit hole on this one. 

As I understand it, the output of a fluxgate transducer is really a combination of 3 things:
- fluxgate for accurate DC and low frequencies
- Conventional current transformer for high frequencies
- Hereward Transformer / amplifier to improve the low frequency response of the conventional current transformer.


Hereward Transformer: use feedback and a second coil to increase the effective magnetizing inductance, thereby reducing the cutoff frequency of a conventional current transformer.
https://cds.cern.ch/record/1068123/files/cer-002723994.pdf

I attached a version of Lymex's schematic with major blocks identified.  I think its missing some detail around the modulator section.

[Echo88]

Sorry, took me a while to find my old reverse engineered schematic from some years ago.
I assume its from a 867 or similar DCCT (cant remember for sure), as its missing the transformers on the older 866.
Hope it helps and you can find enough similarities to your board, my schematic is missing the relay though.

[WallWart]

Thanks for looking through your archives, Echo.  I think we have slightly different models - which makes 3 if you count Lymex's schematic.   For what it's worth, I traced out my board too.  The circuit topology is pretty complete for the 867-700 model I have but  I didn't record many of the component values yet.   The PCB appears to support multiple loadings but I didn't trace the no-loaded section.



Happy New Year Danfysik 867-700 no values.pdf (349.52 kB - downloaded 44 times.)

[Echo88]

Found more stuff.
My schematic is indeed from a 867-700SM (as far as is noted by me), apparently you have a different variant as you said.
Attached are pictures of a my depopulated 867-700 and the BOM.

[WallWart]

For anyone else interested in fluxgates, these videos are really informative. For me, the key idea is that asymmetry in the inductor current from saturation causes even harmonics which can be demodulated or otherwise detected very accurately. There are some simple simulations for anyone playing along at home.

[WallWart]

Those are some very neat and tidy PCB scans. Mine look like they were done with a dull crayon.   Nice work, Echo.