I repaired my 15C back plate



#2

Some time back, I posted with a question regarding repairing the back of my 15c, where the metal plate was peeling up. A number of helpful comments were posted, and so I got to work! Following Randy Sloyer's suggestion, I first removed the rubber feet, disconnected the screws, and took care in lifting the back of the calculator off, so as not to lose the Electrostatic Discharge spring connectors (thanks for the head's up Randy!).

Then, I soaked the back in heptane. now, I remember being able to buy heptane in 1 gallon quantities back in the city (Philadelpha) but now I am in the country--so I used "white gasoline" instead (camp stove gasoline, aka naptha (but not *real* naptha)). I used a narrow, very sharp "k-bar" knife to gently pry the back off--which of course caused it to roll up a bit. Once I had it off, it was generally easy to flatten it using a rolling pin. (In retrospect, one of my cooking knives is even thinner and would have been better).

Finally, with all the glue residue cleaned off, I applied double sided carpet tape to the calculator back, and then applied the metal plate, working from middle to edges. I may go back with a "vacuum bag" to suck it down really tight. (Vacuum bagging is a common practice in the production of high quality fiberlgass or "composite" parts. You merely put a plastic bag around the part that needs to be squeezed, and suck out the air. the result is 14.7 psi pressure on the part).

Mistakes made:

I was impatient. This is always a problem to be dealt with. In a moment of indescretion, I slopped a bit of acetone into the glue joint---having forgotten that the calculator is made of polystyrene! Acetone dissolves PS, and so some of the "tooth" is gone from the outside, and I have discoloration and a permanent fingerprint. Oh well, I knew better, so serves me right!

In peeling the back off, before I rummaged around for a really narrow knife, I started out the cleaving process using a too-dull knife, and this left some permanent ridges in the back --maybe 3 mil (0.076 mm) deep--which were not removable with the rolling pin. Perhaps a small printing press would do the trick--but then I might damaged the silkscreened back labels.

It is interesting to note that in the original construction, a double-sided tape was used--both for the feet, and for the plate, though they are of different kinds--perhaps in order to deal with the higher compliance of the rubber feet, a more compliant tape was used there.


I have flatbed scans of the pieces, if anyone would like to see them, please e-mail me at bill at plattdesign dot net.


Best regards, and thanks again to all who posted help,

Bill Platt


#3

You may send the scans to vDOpNOTnSPAM@welho.com
Remove the DO NOT SPAM before mailing.
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