Cleanup and repair of an ESI Dekastat model DS1463 12K Ohm coaxial decade resistor.
The ESI (Electro Scientific Industries) Dekastat DS1463 is a 3 decade plus rheostat precision resistor. It has an initial accuracy of +/- 0.01% + 1.5 dial division with 10.5 Ohm rheostat and a maximum resistance of 12.1105K Ohms.
There are six resistors per decade using mica wire-wound card resistors. On the 12K Ohm model the first decade has 12 positions and is incremented in 1K steps to 11K Ohms. The second decade has 11 positions and is incremented in 100 Ohm steps to 1K Ohms. The third decade also has 11 positions and is incremented in 10 Ohm steps to 100 Ohms. There is a 10.5 Ohm rheostat in series with the three decades that uses a shorting bar for adjusting it’s resistance.
The resistors in each decade are configured with 5 each 2R resistors in series and one R resistor, where R=1K Ohm for the first decade, R=100 Ohm for the second decade, and R=10 Ohms for the third decade.
For example if 8 is selected on the first decade then the first four 2K Ohm (2R) series resistors are connected to the next decade for a total of 8K Ohms. If 5 is selected on the first decade then the first two 2K Ohm (2R) series resistors are connected to the 1K Ohm ( R) in series, and the remaining three 2K Ohm resistors are shorted to the input of the 1K Ohm resistor for a total of 5K Ohms.
I purchased my DS1463 from a seller on Ebay and it arrived well packed and in good shape. Initial testing showed several decade positions well out of tolerance, and several open circuit positions.
It was time to open the cover and see what was going on inside.
Inside the cover there were no metal shavings or burnt-up resistors. Off to a good start. A quick check of the resistors showed all were in tolerance. That left the ceramic wafer switches as the culprit.
After a thorough cleaning with DeoxIT D5 and a rinse with 99.9% isopropyl alchohol including the rheostat, I followed up with DeoxIT Gold contact conditioner / enhancer.
After reassembling the unit I checked all positions on the three decades with my Keithley 2015 6½-digit multimeter. All positions were well within specifications with no issues from the switches.
Here is a link to the User and Service manual for Decastat models DS 1265, DS 1365, DS 1463, and DS 1464