Electronics > Metrology

3458A, Elantec EL2018CN obsolete?

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franklin:
This EL2018CN seems to have vanished from inventory of suppliers like Digikey as well as others. I can however find it on eBay. I’m in no need for this IC, just curious. Is it obsolete?

In my 3458A (probably manufactured 2011-2013 and bought new in Norway by a company in 2013; previous owner) there are two patch boards with EL2252CM. TiN has mentioned this patch board in “Repair of second HP 3458A metrology DMM”.

A2 (ERC 5314): Patch board replaces U501. There is also a strap that makes this patch board a little different from the patch board on A3. Because it’s replacing only one EL2018CN?
See picture 1.

A3 (ERC 5145): On this board there is a single EL2018CN, U181 and a patch board replacing U142 and U405.
See picture 2.

I wonder why they didn’t replace U181 with the same patch board as in A2?

Finally, I would again like to thank Dr. Frank, Kleinstein and others who contributed with their knowledge, expertise and suggestions to a successful repair of my 3458A in 2020.

Franklin

Kleinstein:
Finding the extra boards to replace the EL2018 is a clear indication the parts are obsolete and very hard to get even for HP/KS. So it is no longer available already for quite some time. There seem to be no direct replacement and likely also limited need. Chances it is no longer produced because of processes from the original source Elantec are no longer available. For the new black eddition they use a different comparator with extra +-5 V regulators and input protection.

U181 is an odd one. I still don't fully understand this part. From the circuit I see absolutely no need for this to be a super fast comparator: it compares ground to a signal from an LM358. A LM311 / LM393 should be suficient here,  if this part is enabled at all. It could be enable funtion why this chip is used.

The patch boards may be different age and added when refurbishing the boards.

martinr33:
The China brokers still have some inventory. I've picked some up.

In most cases, they are obvious remarks. Pefect flat tops, beautiful white lettering - and incorrect logos and too-shallow notches from the grinding.

In other cases, they look legit but are clearly pulls, with straight legs and "socket scratches" on the metal.

Finally, there are few with original-looking markings and correctly angled legs.

Probably not a bad idea to repro the adapter boards.

On the apparently unnecessarily fast comparator at U181 - sometimes, it is better  to use common parts across the design. It may be that it was just cheaper to use the Elantec part than another comparator.

Maybe it is possible to salvage U181 by replacing it with an available part - that is worth a look.

syau:
Bought 6 from a vendor in China, each cost around USD$2. NOS, no solder on the legs.

[attach=1]

Did a side by side comparison on a A3 board U181, looks identical  :-DD

[attach=2]

Kleinstein:
The optical impression looks OK, but there are plenty of good looking fakes.
As these are DIP package, one could do a quick electrical test on a bread board. So is the supply current about right ?

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