Fixing small plastic... things

Tony Eros tony.eros at machm.org
Fri Dec 3 09:06:20 CST 2010


I wonder -- would this be a good application for a 3D printer?

-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
On Behalf Of Josh Dersch
Sent: Friday, December 03, 2010 2:46 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Fixing small plastic... things

Hi all --

Got myself a Friden 1162 desktop calculator.  This is from about 1968-69 and
has a neat-O keen CRT display and uses a magnetorestrictive delay line
memory.  Kinda cool.

Mine has taken a fair amount of abuse over the years, and is currently not
working properly -- at the moment it powers up (with nominal voltages, etc)
and displays a normal display of all zeros, but as soon as a key is
depressed, the screen goes blank and never returns.

The 1162 has a rather interesting keyboard encoding mechanism (you can see a
decent overview of the device & the keyboard mechanism here: 
http://www.oldcalculatormuseum.com/friden1162.html)  Close investigation of
the keyboard mechanism on my specimen reveals that a few of the plastic
"fingers" that are positioned on the rods that move the magnets to/away from
the reed switches have snapped off.

I have a close up picture of what the fingers are supposed to look like at:

http://yahozna.dyndns.org/scratch/friden/normal-finger.JPG

And a picture of one of the broken ones at:

http://yahozna.dyndns.org/scratch/friden/broken-finger.JPG

The broken fingers no longer make contact with the mechanism, and so a
couple of the reed switches do not get activated properly.  I'm guessing
that this is at least part of the reason the machine is acting the way that
it is (that it's getting unexpected scancodes from the keyboard and going
off into the weeds...)

I need to figure out how to "recap" these fingers.  I don't have a lot of
experience repairing plastic stuff like this, anyone have any suggestions?

Thanks!
Josh





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