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Schlumberger Solartron 7040 DMM - Sorry no teardown...

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david77:
...simply because I can't get the damn thing open  :-[.

This 4,5 digit DMM has recently found it's way onto my bench. I can't say much more about it than that it's spot on on all ranges. It's got autoranging (lovely clicky relais affair) and a very fast update rate - the fastest of all the DMM's in my lab. I'd guess about 8-10x a second, the read out updates nearly in real time.
I don't know if it's supposed to be TrueRMS or not but it agrees exactly with the HP400F, so my guess is it is TrueRMS.
Date of manufacture probably early 70ies, information on this instrument is quite scarce I haven't been able to find anything about it, no specs, no manual, nothing.

And yeah, it defeated me. I can not open it, all I managed was to get the back off. There are three PCB's in the case, each on its own slide mount. There are no screws that hold them in place.
I nearly wrecked it when I pulled the knob off thinking there might be a nut or something under there - not so.
Luckily I got the knob back on and have now ceased further disassembling experiments, it works so there's no need to open it apart from curiousity and - as we know - that killed the DMM or something  ::).

From what I could see it looks like there's no LSI in there, all relatively discrete. Only lots of opamps in TO99 cans.

If anybody's got any info on this thing it'd be much appreciated.

tekfan:
Very nice little meter. Always liked the LED display on older multimeters not that LCD garbage.
Is there a range hold function somewhere or does it constantly autorange?


--- Quote from: david77 on December 02, 2011, 10:34:30 pm ---I don't know if it's supposed to be TrueRMS or not but it agrees exactly with the HP400F, so my guess is it is TrueRMS.

--- End quote ---

Well the HP400F is not a true RMS responding meter. It is average responding. If you hook both the HP and the Solartron to a function generator and feed in a triangle or other waveform with a strange shape and if both meters follow eachother then you'll know that the Solartron is not true RMS responding.

david77:
There's no hold function it is always in autorangeing mode. In DCV mode with nothing connected to the inputs that's a bit annoying, it switches ranges about once every 90 seconds when the input buffer overflows and the range switching relays are quite loud.

You are right, of course it is average responding. It was late when I sent off that post, should have noticed that.

Bored@Work:
I don't have experience with that particular model, so take the following with a grain of salt.

Try to detach the handle. Typically you have to move the handle to a particular position (e.g. 90° above the instrument or behind the instrument) and then you can pull the lugs out of the pivot points on each side. If you see any screws at the pivot points stop for a second and try to figure out if they fixate the case or if they are problably part of some delicate, spring loaded pivot mechanism. If it looks like the later consider refraining from removing the screws.

Also look for screws below any standoff rubber feet on the bottom (however, IIRC my 7150plus has screws under separate plastic caps near the rubber feet).

david77:
@BAW: Thanks for the hints but I've checked the handle and have not found a way to remove it. The case is one molded piece that can't be popped open. The only way to get inside is through the back, the back plate is only held in place by two thumbscrews. The three boards rest on separate slidey thingies (here my english leaves me) that are part of the case.
The meter originally had no rubber feet so I put some adhesive rubber feet on and as such I'm sure there are no screws under them ;).

You may well be right that the handle's got something to do with it but how I couldn't tell.
I had cases where the handle could be removed in one particular position but this one doesn't.

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