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Schurr Cable Replacement



 
Schurr and Scheunemann use very high quality shielded cables for keys and paddles, and the odds are very good that you will never have to replace one.  An MMK straight key came in recently for cable replacement-- the first we've done-- so we took advantage of the opportunity to document the process.

In fact, the cable was fine, but the key had seen heavy use for a decade, and the user-installed plug had failed.  The user  thought it would be prudent to replace the entire cable.

1. Access to the Cable Connections

In all of the solid brass base keys and paddles, there is a milled recess for the cable connections (and access to other screws) concealed by a plate.  The plate can be a metal foil label, a thin brass plate, or a plastic plate with a thin brass surface on one side. This plate can be removed by carefully prying it up from one edge.  Sometimes it is  not possible to remove it without damaging it.  If it is damaged too badly to reinstall, don't worry about it-- its function is cosmetic and security only.

What you see will resemble the "after" photo below, with appropriate variations for type of equipment.  Make a note of which wire is connected to which terminal.  In case you forget or are confused, the terminals will be directly underneath the relevant part of the mechanism above.  For example, in the "before" photo below, the connection in the middle is common or ground.  The connection on the right is directly beneath the lower contact, and is there for the "hot" terminal.  If in doubt, check with your multimeter.

Where the cable enters the milled recess, it is "locked" with a blob of flexible adhesive.

2. Remove the Old Cable

Carefully unsolder the connections to the terminals, using a solder pump or wick to remove excess solder.  Pry the adhesive loose and remove it, and then you should be able to pull the damaged cable out through the hole in the base.  Later Scheunemann paddles have a machine screw in the base, centered toward the cable entry hole in the end of the base. Loosen the screw with a hex key (Allen wrench).  If the cable is broken at its entry to the base and you can't reach it, you can pull it through into the recess.

When you have removed the old cable, the recess should look like this:

before
Schurr MMK, before installation of new cable.
Click to view in full size.

3.  Prepare and Install the New Cable

Insert the new cable into the base so that it extends to the most distant connection.  Mark a point on the outer insulation about 1/4" in from the entry point.  Remove the cable so that you can work on it more easily.  

Strip the outer insulation off to the point that you marked.  Separate the shield and twist the strands together to form a lead.  Cut the conductors and the shield lead to the required length and remove 1/4" of insulation.  Tin the end of each lead.

Insert the prepared cable through the hole in the base.  Solder the connections.  Check for continuity between the relevent part of the mechanism (e.g. base, lower contact, etc) and the plug or wire on the other end of the cable.  Lock the cable in position with a blob of hot-melt glue, dope, or other flexible adhesive, and/or by tightening the set-screw..  Replace the cover plate if it is not too badly damaged, and get back on the air!

after
Schurr MMK, after installation of new cable.
Click to view in full size.
 

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