HP42S Changing Back to Clear

[DanM]

I've temporarily returned from the land of the lurkers to report that I finally got around to installing the clear HP-42S back which I got from Chuck McCord at HHC 2018 (San Jose) onto my user-model 42.

Take all the shots at me that you would like to regarding doing this to both a mostly-original calculator and an absolutely pristine clear back from the HP-Corvallis way-back machine... it's done already and since you've now seen it, you have to live with the knowledge. :-)

The calculator is my "backup" 42, which I traded something for many years ago. My original 1-owner 42 remains untouched by projects like this. A previous owner of this "backup" both melted off the SN, and melted in their initials or something into it.

I convinced myself that a clear-back 42 is more worthwhile to me than a regular 42 and a clear back. Also I magically changed this one to "Made in USA" from "SINGAPORE".

Enough of that.

I followed Paul Brogger's guidelines to open up the calculator. ( https://www.hpmuseum.org/cgi-sys/cgiwrap...i?read=199 ) The 4 hidden heat stakes troubled me a little bit, but after application of enough force (a lot of force!) they eventually broke off and the back came off. I did move the beeper to the clear back, but I did not move the metal plate, because I wanted to see the calculator PCB. And I'm not quite sure what that does to the operation, but I think I may have trouble passing a RF-interference test now. But operation seems OK. The Clear USA back has slightly different fastening method than the original issue SINGAPORE one, and it appears that it will hold onto the body reasonably well and be reasonably easy to take off if I want to do so.

Thanks, Chuck!

[Dave Britten]

I got very far in this post wondering "How in the hell does disassembling the calculator help you change the backspace key into clear X?"

[Dwight Sturrock]

Clearly, this is very cool!

[rprosperi]

Hey Dan!

Bold move, nice result!

Leaving out the metal plate leaves a delightful view of the 'guts' and it's fairly unlikely the FCC will see this post and come to your house to check EMI emissions; the pandemic has slowed them as well.

Thanks for sharing this

[KeithB]

(09-01-2020 12:31 PM)rprosperi Wrote:  Hey Dan!

Bold move, nice result!

Leaving out the metal plate leaves a delightful view of the 'guts' and it's fairly unlikely the FCC will see this post and come to your house to check EMI emissions; the pandemic has slowed them as well.

Thanks for sharing this

But you might be able to use an AM radio to play tunes! ISTR this being a thing whey back when. Maybe with an Altair.
(Edited because I spelled "way" as "whey"!)

[Craig Bladow]

This reminded me that Chuck gave me a clear back at HHC San Jose 2018. I received another one from the prize table at HHC Reno 2019, but gave it away to someone, I don't remember who, who really wanted one.

The detaching of the piezo from the original back seems to be somewhat of a irreversible step due the plastic stakes being melted over the edge of the piezo. How is it attached to the clear back?

   

[DanM]

(09-02-2020 01:44 AM)Craig Bladow Wrote:  The detaching of the piezo from the original back seems to be somewhat of a irreversible step due the plastic stakes being melted over the edge of the piezo. How is it attached to the clear back?

The detaching wasn't too bad, and is not completely irreversible. I used an Xacto knife to slice off only the portion of the melted-mushroom head which went over the disc. That leaves enough material remaining on the rest of the mushroom head that one could melt it and push some back over the disc to hold it in place good enough.

The clear back has 4 plastic spikes surrounding the space where the piezo should go. I heated them up with a heat gun, and smooshed 2 of them enough to hold the disc in place. I couldn't do as nice of an industrial job of it as HP did, but mine should hold it in place throughout the ordinary stresses i expect it to receive while being used in my care.