Documents for Calibrator "Calibratore Elettronico TIPO CEM1 / ESLAB" from Italy?

[kblue]

Hello there!

Mayhaps in a remote chance, someone knows something about this thing (as it is currently not running/working). I already checked some supply voltages like +/- 5 V, +/- 15 V, 12 V, 24 V and so on (whatever was labeled). This unit is rather compact, weights about 9 kg and it would be great, if this thing would work. With less than 10 kg it would be, at least for me, a better "portable solution" for local tinkerer meetings and casual "DMM checks" compared to my big, old Fluke Calibrators.

I don't even know, if this thing was a "proof of concept" or something, as it has lots of bodgewires and an electrically unconnected front panel meter (40.000 counts). It seems to be build around a REF02EJ. Someone was already in the unit, as some caps are from the magnificent, the legendary, the company made out of pure wisdom ... ChongX. On the ANL (analog?) board with the reference i found a shorted ChongX cap (-5 supply with a local 79L05) and changed it already as most of the other caps are changed aswell (except the big filter caps, they seem to be fine).

There is no "output" in neither function (DC, 50 Hz, 60 Hz, 400 Hz). The unit seems to be running internally with 400 Hz (was able to find the frequency going into the DAC0800 on the LOG board). I guess the principle for generating different DC voltages/amps is comparable with some old Fluke Meter Calibrators like the 760A which does run at 400 Hz too internally.

What was done so far:
- checked voltages (at least whatever i was able to locate)
- changed caps (except big filter cans)
- checked 79L05 and 78L05 on the ANL board
- checked the 74S472 TTL-PROM (which i guess i kinda the "brain" of the unit and it seems to be working)
- checked most of the 74-logic ICs with my XGECU tester and they seems to be fine
- checked the OpAmps with a cheap china OpAmp tester and they seem to be fine too
- checked REF02 output: which is very stable and working
- checked most of the relays (some are always not active, selected mode or range does not matter, i guess some relays only go active if the unit is running)

Was not able to test things like LF13331, LM311, DAC0800 and so on. The unit is full ... i mean FULL with 2N7000s like whoever build this thing raided a warehouse or something. These things are everywhere!

Asking for any information might be a long shot, but oh well - mayhaps someone stumbled upon such a unit in the past or knows something about it.

Here are some pictures:

[kblue]

So far, no information, no documents found. I tried several reverse images search requests with full or partial images from the frontplate and/or text. I stumbled upon other "small calibrators" in this form factor from other countries and they are often used for lower counts panel-meters or multi-meters. But this would be finde for some rudimentary checks on the go if this would work again.

Mayhaps its one of a kind, who knows. Analysing the possible fault will be a challenge Still searching the net and asking our god and saviour "AI".

Best wishes!

[kblue]

Lucky me ... still no schematics, but DC output works again and is surprisingly stable for such a little unit. Problem was some sort of short between a N-Channel JFET (ANL Board) and GND which was close to invisible because it was just a very, VERY tiny part of the big GND-plane which came lose.

AC does not work ... yet. Lucky me again, some more LEDs are now active again and if i switch to 50 Hz, 60 Hz or 400 Hz AC mode, the "section" which should be active is indicated with a red LED. I probed around this section of the ANL-board and found a internally shorted N-Channel JFET (2N4091).

I dont have much "JFETs" in stock, guess i need to order some parts (mayhaps mordern replacements?)

But anyhow - Progress was made!

/edit: I dont know if this will work, just for testing purpose but i found half of a FD1757 (in the manual as E7024) (half ... because 3 of 6 legs are missing) from some old Fluke Multimeter which identifies as a N-Channel JFET in a metal case but no datasheet so far.

[Kleinstein]

For the 2N4091 chances are one could use a more common 2N4391 / PN4391 / J111 as a replacement. They should be from the same process, and more like different testing.