Some Kelvin Varley pron showed up during repairing the cheapest KVD available on
eBay when i felt I need a little brother of my RV722 O0. There was a device on ebay USA employing a Electro-Measurement Inc. (later ESI) DV411, together with a power supply. Everything besides the Divider was removed, the remaining problem was the third decade switch was not latching to the digit positions
![Scared :scared:](https://www.eevblog.com/forum/Smileys/default/scared.gif)
. So i removed the three screws and opened the second can (my coworker from Taiwan was reminded of landmines
![Evil >:D](https://www.eevblog.com/forum/Smileys/default/evil.gif)
)
Overview picture
![](http://dg3hda.primeintrag.org/lib/exe/fetch.php?media=overview.jpg)
Above you see the switch without the latching mechanism on top,there is a inner and a outer ceramic wafer, the inner one is turning with the outer drive shaft and has the moving contacts. The outer part is fixed.
Under it the resistors that make up the rest of the KVD network. The second decade here is realized by a potentiometer with two fixed R in parallel, in the first can with 2 decade switches i would simply expect that it repeats.
![](http://dg3hda.primeintrag.org/lib/exe/fetch.php?media=potentiometer.jpg)
The Potentiometer without its cap. Although sporting 270° range, it is really turning 360°. Asked the gurus at volt-nuts, they confirmed this strange behaviour is okay.
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif)
![](http://dg3hda.primeintrag.org/lib/exe/fetch.php?media=locking_cogwheel.jpg)
The broken latching mechanism short after repair-the cogweel on the drive shaft is intended to be locked in positions by a ball-on spring. The cogwheel was loose, but to my surprise only soldered to the drive shaft.
![WTF? :wtf:](https://www.eevblog.com/forum/Smileys/default/wtf2.gif)
Employing a agressive flux, that is what I reworked after repositioning the wheel on the shaft.
After putting everything back together in its housing it has shown to be a sucessful repair.
It divides on demand, Ratio is good for 4 decades and the 5th depending on operators skills
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
Cons: US screws! The handwheels had to kiss TORX 7 to align to the shafts, not the real US imperators imbus.