28S Heat stake size? (Repairing a mostly working 28)
05-15-2018, 08:27 PM (This post was last modified: 05-16-2018 12:12 AM by wyatt8740.)
Post: #1
 wyatt8740 Junior Member Posts: 8 Joined: May 2018
28S Heat stake size? (Repairing a mostly working 28)
Hi. I bought myself a HP-28S as my first RPL calculator a while back (with an intact battery door!), and I love it. I'm planning on getting a 48SX or 48GX eventually, but I really, really like the full alphabetic character set on the clamshells, and as an occasional LISP/Forth programmer appreciate the rigorous and consistent RPL approach the 28 takes, spartan as it may be compared to the relative 'luxury' offered by a 48. So I'd like to keep my 28 around. Unfortunately in the last few weeks it's started acting up (arrow keys don't all work unless pressing down on the shell).

I see on the forum archives that at least two people have fixed their calcs with styrene rods and new foam, and I'd like to take that route, but I cannot currently take the stickers off the calculator to measure the rods. The HP journal article on the 28C, which describes the manufacturing process and includes internal photos, does not give measurements on the heat stakes either.

If anyone has one of those rare translucent ones, or a 19BII with the battery cover on the back (you can see the stake holes in the battery bay), or has done this and remembers/can measure, could you tell me approximately how thick the rods I should buy would be? My eyeball guess is around 2mm diameter, but I don't live in a metric system country and only have a vague idea of how big a millimeter actually is.

Also, is the foam replacement a vital part of making the keys work again? Or is it just something people like to get done while they have the calc apart?
05-16-2018, 03:52 PM (This post was last modified: 05-17-2018 11:52 AM by jebem.)
Post: #2
 jebem Senior Member Posts: 1,303 Joined: Feb 2014
RE: 28S Heat stake size? (Repairing a mostly working 28)
If you can't contact Geoff Quickfall, try reach this other member at his site as apparently there is also a project for creating a new case from scratch and probably you can get the correct rod sizing there.

That said, sooner or later you will have to open the calculator to fix it, and then you will will be able to take all the measures you need.

ok, I took some readings on my 19BII:
base, outer: 5mm or 0.197" or 13/64"
base, inner: 3mm or 0.118 or 1/8"
the rod: 2mm or 0.079" or 5/64"
Some more details here.

Neil Hamilton (Ottawa) member have posted the information you are looking for.
According to him, he used 3/32" styrene tubing instead of rods, and then he realized it was a little bit thicker than required to install them without additional corrective actions, so he used a little bit larger diameter than my measurements above at 5/64.

Jose Mesquita

05-28-2018, 04:06 AM
Post: #3
 wyatt8740 Junior Member Posts: 8 Joined: May 2018
RE: 28S Heat stake size? (Repairing a mostly working 28)
Sorry for the lateness of the reply. Thanks so much for checking!
For some reason, the arrow keys have started working again for now, so I'm going to put off actually redoing the stakes until it acts up again.

I'll try to contact Geoff, too. Somehow didn't even really realize that I could do that.

Wyatt Ward
Computer history enthusiast
05-28-2018, 04:09 AM
Post: #4
 wyatt8740 Junior Member Posts: 8 Joined: May 2018
RE: 28S Heat stake size? (Repairing a mostly working 28)
P.S.
I just picked up a 48SX, so now I will have an RPL calculator to mess with if I break something badly when servicing the 28S. I think that will make me get to actually taking it apart a lot quicker, since I now have a fallback plan.

Wyatt Ward
Computer history enthusiast
05-28-2018, 01:42 PM
Post: #5
 rprosperi Senior Member Posts: 3,541 Joined: Dec 2013
RE: 28S Heat stake size? (Repairing a mostly working 28)
(05-28-2018 04:09 AM)wyatt8740 Wrote:  P.S.
I just picked up a 48SX, so now I will have an RPL calculator to mess with if I break something badly when servicing the 28S. I think that will make me get to actually taking it apart a lot quicker, since I now have a fallback plan.

Since you now have a 48SX, it's likely you'll stop wanting to use the 28S. The 48SX is just so much better in every way, it's hard to imagine wanting to go back.

And though it would be easy to only use '28s features' on the 48SX, definitely explore the expanded commands, as they offer much more.

Bill Wickes book "HP-48 Insights Part I - Principles and Programming" is a great (likely the best) resource for learning the 48SX, even if you already know RPL from the 28s. It's included in the MoHPC Document Set.

--Bob Prosperi
06-07-2018, 02:08 PM (This post was last modified: 06-07-2018 04:27 PM by wyatt8740.)
Post: #6
 wyatt8740 Junior Member Posts: 8 Joined: May 2018
RE: 28S Heat stake size? (Repairing a mostly working 28)
(05-28-2018 01:42 PM)rprosperi Wrote:  Since you now have a 48SX, it's likely you'll stop wanting to use the 28S. The 48SX is just so much better in every way, it's hard to imagine wanting to go back.
Eh, I'm finding myself disagreeing so far.
The full alphabetic keyboard on the 28S makes programming it much more convenient. I find myself writing my programs on the 28S and then translating them for the 48. I also think I prefer the key feel on the 28S, and I like that it is smaller in my pocket, as well. Additionally, there are some functions that I can't seem to find on the 48SX, such as "RCLΣ", which I have to manually key in.
I also cannot find a 'catalog' button (a very useful feature), and the screen on the 28S is far more legible.
Additional minor annoyances include not having a "roll" button readily available, requiring using the arrow keys (slow) or adding it to the custom menu (takes up space that would be nice for other functions), and that some shifted alpha keys are not printed on the overlay, requiring looking in the manual to find out how to type a "greater than" (>) sign or similar.
The two things I like more about the 48SX so far are its usability in one hand, the fact that it has the "I" part of "I/O", and the ability to recall, edit, and re-store the custom menus rather than rewriting them from the ground up to tack something on the end.
(05-28-2018 01:42 PM)rprosperi Wrote:  And though it would be easy to only use '28s features' on the 48SX, definitely explore the expanded commands, as they offer much more.
I don't own the manuals for the 48SX except as PDF's, but I do own the manuals for the 28S. Having paper copies is really convenient.

(05-28-2018 01:42 PM)rprosperi Wrote:  Bill Wickes book "HP-48 Insights Part I - Principles and Programming" is a great (likely the best) resource for learning the 48SX, even if you already know RPL from the 28s. It's included in the MoHPC Document Set.
Thanks for the recommendation. I really prefer print books, but I am still thinking about getting that CD.
Is there a digital copy/torrent mirror somewhere, like with Linux distributions? Or is it intended to be "physical disc only" to provide revenue for HP Museum?

Wyatt Ward
Computer history enthusiast
06-07-2018, 07:39 PM
Post: #7
 rprosperi Senior Member Posts: 3,541 Joined: Dec 2013
RE: 28S Heat stake size? (Repairing a mostly working 28)
(06-07-2018 02:08 PM)wyatt8740 Wrote:
(05-28-2018 01:42 PM)rprosperi Wrote:  Since you now have a 48SX, it's likely you'll stop wanting to use the 28S. The 48SX is just so much better in every way, it's hard to imagine wanting to go back.
Eh, I'm finding myself disagreeing so far.
The full alphabetic keyboard on the 28S makes programming it much more convenient. I find myself writing my programs on the 28S and then translating them for the 48. I also think I prefer the key feel on the 28S, and I like that it is smaller in my pocket, as well. Additionally, there are some functions that I can't seem to find on the 48SX, such as "RCLΣ", which I have to manually key in.
I also cannot find a 'catalog' button (a very useful feature), and the screen on the 28S is far more legible.
Additional minor annoyances include not having a "roll" button readily available, requiring using the arrow keys (slow) or adding it to the custom menu (takes up space that would be nice for other functions), and that some shifted alpha keys are not printed on the overlay, requiring looking in the manual to find out how to type a "greater than" (>) sign or similar.
The two things I like more about the 48SX so far are its usability in one hand, the fact that it has the "I" part of "I/O", and the ability to recall, edit, and re-store the custom menus rather than rewriting them from the ground up to tack something on the end.
(05-28-2018 01:42 PM)rprosperi Wrote:  And though it would be easy to only use '28s features' on the 48SX, definitely explore the expanded commands, as they offer much more.
I don't own the manuals for the 48SX except as PDF's, but I do own the manuals for the 28S. Having paper copies is really convenient.

(05-28-2018 01:42 PM)rprosperi Wrote:  Bill Wickes book "HP-48 Insights Part I - Principles and Programming" is a great (likely the best) resource for learning the 48SX, even if you already know RPL from the 28s. It's included in the MoHPC Document Set.
Thanks for the recommendation. I really prefer print books, but I am still thinking about getting that CD.
Is there a digital copy/torrent mirror somewhere, like with Linux distributions? Or is it intended to be "physical disc only" to provide revenue for HP Museum?

As for preference of 28 vs. 48 keyboard use and default key assignments, it's hard to appreciate a new machine when you've used another for a long time, but like most, I still think once you adjust to the 48, you won't look back.

I agree that paper books are far easier to read and learn from, though the search feature in the PDF is hard to beat (so, of course, the answer is to have both).

The MoHPC set comes on USB drive these days (outgrew a DVD or CDs) and is very well worth the modest cost. Many user manuals are available online from other sites (some even still from HP), but for almost all of the books, they are not available online as the authors have not granted permission to post their contents online while they have granted permission for distribution as part of the MoHPC Document set.

The Wickes book (start with "HP-48 Insights Part I - Principles and Programming") is often available on eBay and other sites, though the price can vary widely (e.g. currently $50-$435 on abebooks.com). I don't see one listed on eBay now, but I have seen it listed in the past for as low as \$25.

You may want to consider having the LCD in your 48SX upgraded to a black LCD, it dramatically changes the ease of reading and overall feel of the machine. If interested, I can recommend someone to do this, it's a reasonable cost, low-risk, and oddly makes your 48sx seem much "better" than it was. Weird but true.

--Bob Prosperi
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