ESI Dekastat DS1463 12K decade resistor repair

Cleanup and repair of an ESI Dekastat mod­el DS1463 12K Ohm coax­i­al decade resis­tor.

ESI Dekastat DS1463 decade resistor top view of dials and case
ESI Dekastat DS1463 decade resis­tor top view of dials and case

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.

ESI Dekastat DS1463 decade resistor closeup of wire-wound precision resistors
ESI Dekastat DS1463 decade resis­tor close­up of wire-wound pre­ci­sion resis­tors

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.

ESI-DS1463 schematic
ESI-DS1463 schemat­ic show­ing 8.880K Ohms select­ed on the decade switch­es

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.

ESI Dekastat DS1463 decade resistor removing outer case/shield
ESI Dekastat DS1463 decade resis­tor remov­ing out­er case/shield

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.

ESI Dekastat DS1463 decade resistor 10 Ohm potentiometer closeup
ESI Dekastat DS1463 decade resis­tor 10 Ohm poten­tiome­ter close­up

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

DS1463 Coaxial Decade Resistor User and Service Manual PDF

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