clock, no continuity

[DonaldSmith]

My 47 DeSoto clock stopped quite some time ago.  I finally tackled the task of removing the clock and checking it out.  

The clock is held in with a screw and nut at the upper right edge and a screw at the lower left edge (seen from the back of the instrument panel, which is actually the front).

 

I removed the light assembly for the glove-box and ashtray to access the lower screw.  It was still ab itch to get the screw out.

 

 

I disassembled the clock.  The insulated post is to the left and the post grounded to the case is to the right, at the bottom of the photo.  

 

 

I found continuity from the grounded post to the contact points; both points are closed, which would power the solenoid and wind the clock for a minute or two.  But there is no continuity between the posts, that is, through the solenoid, at any setting of my ohm meter.  I am stumped.  Maybe I will disassemble the clock further, to trace the circuit through the solenoid coil.  With luck, the break will not be in the coil itself.  

 

Clock gurus may chip in. 

 

 

[Plymouthy Adams]

first divide the continuity test into points/winding  read across the points only..this usually need burnishing after a period of time..they get glazed and build a high resistance on the surfaces...if the points test open...clean contacts....if however they read good from get to..you will proceed to the windings of the electromagnetic coil...verify grounding points..any bit of loose fitting and arcing to ground over time again builds a high resistance carbon glazing,...

[DonaldSmith]

Found it!  Broken solder connection between the solenoid coil wire and a copper strip.  Now I need some fine soldering work

 

 

(I'll check the resistance between the loose wire and the other end of the coil, to make sure that the rest of the coil is OK.)

Edited June 9, 2015 by DonaldSmith

[DonaldSmith]

It works!  I had to get a little resin flux on the end of the copper brass strap and hold the strap against the wire while soldering and cooling.

 

 Continuity checked OK.  Reassembled the clock and attached the power wire to the in-line fuse.  Grounded the clock case.  Klunk!  It wound!

 

Reset the time, will check.  (They never run completely accurately, but it's the periodic clunk and the tick, tick, tick that are important.  Those sounds remind me of sitting in my dad's car and daydreaming.)