Miracles can happen

[grsbanks]

So I see this HP-28S going on TAS for a really good price (£50, so roughly $65) and I think to myself that it's got to be in really rough state if someone is selling a "working" 28S at that price. I went for it anyway as I have another 2 clamshells and should be able to get something that works with parts from the 3 of them.

It arrived yesterday and the first thing I did when I got home from work was rip the parcel open to take a look at this machine.

It turns out, it's in really great condition. It passes all the self tests. The case is solid, no cracks. The rubber feet are all there and they look virtually unworn. There is no corrosion in the battery compartment and the battery door is virtually as new.



This 28S looks almost brand new. Needless to say, I am a very happy bunny

There are still some good bargains out there!

[Trond]

I don't get what's being shown in the picture, relative to what you are saying here.

[John Cadick]

The most common failure point for any of the clamshells is the battery door. It frequently breaks. He is showing that the battery door shows no sign of failure.

[rprosperi]

(12-16-2017 06:16 PM)Trond Wrote:  I don't get what's being shown in the picture, relative to what you are saying here.

You clearly have never owned one of the clamshell models.

You will likely never again see one which has such perfect battery door and door frame (no cracks, chips, broken slot, bent metal runner, etc.)

Christmas miracles come in all forms, so congrats grsbanks on a great choice. Sometimes when you gamble, you win, even when buying calculators...

[Dave Frederickson]

Besides not putting batteries in the calculator, is there anything you can do to prevent the door from cracking in the future? Would something like Armor All help rejuvenate the plastic?

[DA74254]

(12-16-2017 06:44 PM)Dave Frederickson Wrote:  Besides not putting batteries in the calculator, is there anything you can do to prevent the door from cracking in the future? Would something like Armor All help rejuvenate the plastic?

I really cannot answer you here. Though my door is intact, but whenever I replace the batteries, I "forcibly" pushes against the batteries when sliding the door shut. Don't know how many times I've replaced the batteries, but I've had it in working and live order with batteries in it constantly since I bought it in 1992.

[grsbanks]

(12-16-2017 06:44 PM)Dave Frederickson Wrote:  Besides not putting batteries in the calculator, is there anything you can do to prevent the door from cracking in the future? Would something like Armor All help rejuvenate the plastic?

I'm always loathe to put any kind of chemical product on these plastic parts. Most of the time they end up making the plastic even more brittle and less resilient, so they do more damage than good long-term.

It may have looked cool when it was thought up but it's not really a practical design because the only real way to make as sure as possible that it won't break is not to put batteries in the machine. Now, if only the designers at HP had thought this through and not put springs in that require approximately 6 tons of pressure to push the hard-to-come-by LR1 cells down sufficiently to slide the door in...

Hindsight is a beautiful thing

[d b]

I've had (and heard of) real bad luck with using Armor All on things like padded dash boards and soft plastics. Since I know nothing about the chemistry of plastics, that leads me to not use it on irreplaceable calculator bodies.

[grsbanks]

Has anyone 3D printed replacement parts for this series of machines?

[EugeneNine]

Thats what I was thinking, 3d print a replacement door for daily use and keep the original put away for show.

[rprosperi]

(12-16-2017 07:24 PM)grsbanks Wrote:  Has anyone 3D printed replacement parts for this series of machines?

More often than not, it is the door frame (part of the case housing around the door opening) that breaks, and replacing this part requires destructive disassembly of the entire unit.

Also, the door has a thin spring metal tab (used to connect the upper and lower batteries in series) which must be very rigidly attached to the door as its edges slide under the door frame to retain the door.

In other words, the very poor design (worst of all HP battery doors, IMHO) precludes a fix with a simple 3D part.

[grsbanks]

(12-18-2017 03:14 PM)rprosperi Wrote:  More often than not, it is the door frame (part of the case housing around the door opening) that breaks, and replacing this part requires destructive disassembly of the entire unit.

Yes, I was aware of that rather unfortunate fact of life

While I admit it wasn't explicit in my query, I did mean replacement bodies for the clamshell units, not just battery doors.

[SlideRule]

There was a correction to this 'weak link' with the Door In Back version for the N-Cell battery (x3) access on the 19BII-ii calculator.

[attachment=5445] [attachment=5446]

BEST!
SlideRule

[grsbanks]

(12-18-2017 05:38 PM)SlideRule Wrote:  There was a correction to this 'weak link' with the Door In Back version for the N-Cell battery (x3) access on the 19BII-ii calculator.

I wish mine had that

[mfleming]

(12-18-2017 03:17 PM)grsbanks Wrote:  

(12-18-2017 03:14 PM)rprosperi Wrote:  More often than not, it is the door frame (part of the case housing around the door opening) that breaks, and replacing this part requires destructive disassembly of the entire unit.

Yes, I was aware of that rather unfortunate fact of life

While I admit it wasn't explicit in my query, I did mean replacement bodies for the clamshell units, not just battery doors.

There is a great article showing a teardown and rebuild of the HP-19B clamshell. That should convince you that a replacement body would not be the way to go! However, at the end of the article the author shows a nice handmade widget for holding in the batteries where the door had broken away.

http://www.hpmuseum.org/cgi-sys/cgiwrap/...?read=1150

I thought I once read that someone had made up and sold a few of those brackets. Perhaps a 3D printed plastic version with a metal strip at the battery end might one day be offered.

~Mark

[grsbanks]

(12-19-2017 01:25 AM)mfleming Wrote:  http://www.hpmuseum.org/cgi-sys/cgiwrap/...?read=1150

Thanks for the link -- I'd not seen that tear-down. Bookmarked!