Wednesday October 18, 2017

Fixing a Stackpole Momentary Keyboard / Key Pad Switch

Author: Wayne Eggert
Date: 05/24/2012


KeypadIntroduction
Today we have a relatively simple fix for a non-working keyboard / key pad switch (momentary SPST) made by Switchpole.  The Stackpole Electronics, Inc. company was founded in 1928 and is a large manufacturer of all kinds of electronic components.  I had an old device that was built by Heathkit in the 1980s that had a keypad with Stackpole switches in it.  The switches were not microswitches so no loud "clicking" is heard when they're pressed.  Anyway, one of the switches was not working and after being unable to find a suitable replacement, I decided to open the switch up to see if it was fixable.

 

Diagnosing the Problem
Unfortunately the switch was sealed together at the factory.  I did not see an easy way of making a clean cut into the swtich and thought it was very likely I'd destroy the switch in the process of trying to figure out how to open it.  I used a dremel with a cut-off wheel and held the switch with a small pair of channel-lock pliers while cutting around the bottom of the switch (getting smarter in my old age) as sometimes the dremel can kick back or slide off as you're using it and I'd rather be able to count to 10 for a good while!  Had to be a little careful around the solder pins on the bottom of the switch.. didn't want to destroy them so I just cut around them.

Luckily none of the internal parts were destroyed after cutting off the bottom and after opening the switch, the simple design was revealed.  The 2 ends of a spring contained in a molded piece of plastic that moves when you depressed the switch make contact with the solder points on the PCB connecting the switch to ground.


Inside the Stackpole Switch
Photo: Inside the Stackpole Switch


Fixing the Switch
The two ends of the spring had been bent out of alignment from heavy use and were no longer able to hit the contact points on the bottom of the switch housing.  I simply bent the ends of the spring down and then tested by holding the bottom on with my fingers, hooking the multimeter up to the contact points & depressing the switch.  The switch worked good as new!

I then used a dremel routing bit to get the plastic switch housing nice and flat for re-assembling.  Then used ultra high-tech hot glue to seal the switch housing back up.  The switch was made a little shorter from the plastic that was cut through with the dremel, so when I soldered the switch back into the circuit board I left it mounted higher on the board.

Sealed Switch
Photo: Switch sealed back up with hot glue.


Final Thoughts
Sometimes you got to do what you got to do to get something working again.  I could have hacked together another switch into the board, but it would have been clearly hacked and affected its use.  Much better if you can find an exact replacement part or fix the existing part.  Switches are usually pretty simple internally, but they do wear & often weren't meant to be opened up.. so luckily this design allowed me to open the switch up and fix it even though the switch housing was sealed.




Comments:
No comments have yet been made.