Thursday, June 29, 2017

Building out 1130 bulb assemblies, begin construction of 1402 relay tester


Today I soldered together more lamp assemblies, eight at a time with breaks to minimize frustration and achy backs. By the end of the day the main board had all its 96 light positions installed. Now that the big board is done, there are a mere 60 to build for installation across the two small boards.


I received all the remaining parts today and began layout of the components inside the project box. I marked up the holes to mount the two relay sockets as well. I located my 20V and 5V power bricks which will drive the coil and contact current.

The design uses 1W resistors to control current through all the contacts, developing about 150 ma on each set and measures the voltage drop of the contacts to determine quality. Small Arduino interface relays fire the 20V pick and hold coils on the relays under test.

I will solder the 1W resistors directly onto the relay sockets, so save the space required for a resistor mounting perfboard as used in the original machine. Thus I just need to mount an Arduino, a small relay board, the two relay sockets, and four LEDs. The two power bricks and most of the USB cable will be outside the project box. 


  1. Wow, such a relay tester would be incredibly useful for maintenance of any unit record gear. And in restoration, where I imagine simple exercising of an old relay would restore its contacts. As I recall there were a couple of sizes of wire-contact relays, the common kind where the frame is about 1/2" wide, and a double-width kind. So does this tester have sockets for both? For that matter, were the sockets standardized enough that the pick and hold coils and the contacts are always the same pins? (probably)

  2. Hi David

    The 1402 has a few types of relays, but the types that cause all the problem are the permissive make 4 circuit and 6 circuit relays. The bigger one is green and has a socket that is standardized, with a slightly narrower socket standardized for the red 4 circuit type.

    This tester will cycle the relay at 1KHz to help remove some oxidation, even if contact cleaner is needed it can be sprayed while they oscillate.

    Then, the tester runs about 150ma through each contact pair simultaneously as it switches at 1KHz. The Arduino measures the voltage drop through each contact and reports that to the user.

    As a rule of thumb, we work on any contact that reports under 90% of the source (5V) supply.

    The user can also individually fire the pick and/or hold magnets to verify their proper operation.

    This particular unit is not set up for the wire contact type as used in keypunches, which are the type you are mentioning, but it could easily be extended to do that as the principles are the same.