ESI RV622A Resistor Repair

[gmilliorn]

I have an RV622 that fails if standing on end, or if bumped laying flat.  I traced it down to one
resistor that has a "bond wire" detached.  It's hard to get a good picture, but the circled area
is detached from the resistor.

All these resistors look like the leads were spot-welded.  I don't have such a tool, is it safe to try
to try to solder the wire?  The end cap is pretty large and I don't want to melt anything.

[scopeman]

That wire is probably manganin or something simiar.

https://en.wikipedia.org/wiki/Manganin#:~:text=Manganin%20is%20a%20trademarked%20name,the%20Bushy%20House%20physics%20laboratory.
https://www.isabellenhuette.de/fileadmin/Daten/Praezisionslegierungen/Datenblaetter_Widerstand/Englisch/MANGANIN.pdf

I am not sure what flux to use but when you find out please post. I saw on YouTube (search soldering Magnanin wire) where it looked like regular tin/lead solder was used but there were  no other details available. I do know that once you fix it you need to coat the solder joint and the exposed wire with a conformal coating to seal out oxygen.

Sam
W3OHM

[gmilliorn]

It seems Manganin can be soldered, based on web searches plus comments from Edwin G. Pettis and
others such as here:
https://www.eevblog.com/forum/metrology/manganin-zeranin-enamelled-wire-availability/

From the close up of another resistor, the Manganin appears to be soldered while the lead is welded.
Even though they look quite different, I assume the end-caps must be Manganin as well, or else the
TCR would be affected?

There are cheap spot welders on ebay, used to weld batteries.  It might be interesting to try one, it's
an inexpensive experiment and would prevent desoldering the manganin wire connection, perhaps.

[gmilliorn]

Reviews of those cheap spot welders aren't very encouraging, and require an expensive LiFePo battery
or such.  The lead wires are about 1mm thich at least.

However, while searching, I found this comment from Earle Rich which discusses making just these
types of resistors:

https://hackaday.com/2021/06/16/review-battery-spot-welders-why-you-should-buy-a-proper-spot-welder/#comment-6357273

A bit too vague to replicate, though.

[gmilliorn]

I could not find out if the wires inside are Manganin/Constantin or just copper.  Since the point of a KVD is to eliminate
the effects of low-ohm switches, as I understand it, then I assume the wires are the same?  All the internal wires are
soldered to the switches.

Little info I could find on soldering manganin, other than a weird pair of youtube videos doing nothing.

In any event, I cleaned the area w/1200 grit sandpaper and cleaned again with IPA, and was able to solder it
relatively quick with no issues.  Either I was luckly or there's no issue soldering it.
3x cleans after soldering with IPA and it seems to be fine.

I can dial in any voltage within limits of my uncalibrated Fluke 8842, below reads as 1.0000V so I guess it is
off about 70mV.

[gmilliorn]

Incidentally, in all my searches I never found any manuals covering the RV622A - only for the
bigger RV722 which is larger values + trimmable, therefore a bit "fancier". 

If anyone knows of one it would be appreciated.

[meandeev]

I have a RV722, which is for sure not trimmable (but has a hidden secret ;-) see https://www.eevblog.com/forum/metrology/kvd-why-1-1-value-on-first-decade/ ), it depends on the age

[gmilliorn]

Hmm, I was basing the adjustment comment on this info in the RV722 manual:

Perhaps they changed over the years...

[Kosmic]

Hmm, I was basing the adjustment comment on this info in the RV722 manual:

Perhaps they changed over the years...

This is the newer version from IET (https://www.ietlabs.com/esi-rv722-dc-voltage-divider.html). The original RV722 from ESI can only be calibrated but not adjusted.