Interesting Subset Ringer Issue

[TelePlay]

Anyone ever seen this before?

Started to work on an old but quite dirty AE Monophone subset/ringer box today. Once I got the ringer out, I tested it and it would not ring.

I found no continuity between the ringer coils but did get about 256 ohms on each coil. Everything looked fine until I put the inter-coil wire connection under magnification. What I found was the big blob of solder connecting the two coils was cracked on a 30 degree or so angle. A close up of the cracked solder connection is on the right from both sides of the ringer. This is hardly visible with the naked eye.

Big question is how could this even happen with no other damage to any part of the ringer or whole subset?

I was expecting a broken wire but not a substantial blob of solder to be cracked in this way. Just passing this along as an example of the unexpected when working on phones and their peripheral items.

[TelePlay]

Re-flowed the solder joint and got 510 ohms across the coils. Hooked up my ring generator and it works just fine.

Based on the well faded label inside the box, I thought it might be a 50 Hz frequency ringer but it works just fine at 20 Hz. Sometimes a problem does not occur when starting to do something new.

[unbeldi]

Old solder joints can indeed fail over time.  Although it may seem that the solder is sort of a frozen liquid, over time it crystalizes along microscopic stress and grain boundaries, until minor mechanical disturbance causes fission.  80 years is a long time for chemistry and physics to obey their laws.

[TelePlay]

Old solder joints can indeed fail over time.  Although it may seem that the solder is sort of a frozen liquid, over time it crystalizes along microscopic stress and grain boundaries, until minor mechanical disturbance causes fission.  80 years is a long time for chemistry and physics to obey their laws.

unbeldi, thanks, didn't realize that. I am familiar with cold solder joints failing but this type of failure was a first for me.

I realized some may not see the crack so this photo shows the failure from two sides, the joint failure is just above the yellow lines.

[unbeldi]

It may have been poorly soldered in the first place, producing a so-called  ''colder solder joint.''  I am sure it was a lot harder to produce good joints with equipment of the time.  The irons were not temperature controlled.

[dsk]

I have had, and made some  ''colder solder joints'' myselves, and they may indeed be hard to find.

dsk