HP 28 misc...

[mdunn]

I told myself I was only interested in acquiring LED machines (already having an HP15 from the old days). But of course got intrigued by the 28, and now have a clean machine on my desk. Some questions & comments:

1. Is the 2-cell tube supposed to be so tight? I really have to whack the calculator to get the cells out. There's a thin strip of diagonally-applied foam in there causing the problem. Opinions?

2. The 28 seems to be the cheapest "serious" HP calc to be found on eBay...by a long shot. Weirdly interesting. Cheaper than LED calcs. Cheaper than the 32 & 42, both of which I wouldn't mind having, but not at those prices. Is it because it's such an unusual machine?


Yeah, quite the machine... :-} I'm gradually working through the manual. It's more a computer than a calculator. Hints of a BASIC machine, but perhaps closer in spirit to Forth??? With a touch of MathCad...? I haven't got to the programming section yet, so those are just first impressions. Though I did manage to create a counting loop.

[Thomas Okken]

The 28 is a lot of fun, but it depends on which model you have. The 28C has only 2 kilobytes of RAM, and that isn't really enough for it to be more than a technology demo. The 28S has 32 kilobytes, and it is capable of serious work.

The main drawback of the 28, and probably the reason why they tend to sell for cheap, is the lack of external storage.

[burkhard]

(06-21-2018 12:31 PM)mdunn Wrote:  1. Is the 2-cell tube supposed to be so tight? I really have to whack the calculator to get the cells out. There's a thin strip of diagonally-applied foam in there causing the problem. Opinions?

I have a 28S and the batteries might need a tiny shake, but nothing violent. I certainly would not "whack" the calculator anywhere around the battery compartment because the clamshell models are so fragile there. I don't see any foam on my 28S.

(06-21-2018 12:31 PM)mdunn Wrote:  2. The 28 seems to be the cheapest "serious" HP calc to be found on eBay...by a long shot. Weirdly interesting. Cheaper than LED calcs. Cheaper than the 32 & 42, both of which I wouldn't mind having, but not at those prices. Is it because it's such an unusual machine?

The LED calcs tend to be expensive because with special batteries and (usually) no continuous memory, many of them have gotten tossed over the years. And, there's a nostalgic market for them.

The 28C is not unusual. It's quite common, which helps it being cheap. Also, the 28S is the same machine in every respect except a few very important improvements (gobs more memory and the ability to use directories). So everyone really prefers the 28S. The advantage of the 28C is price.

For just doing calculations on your desk though, the 28C is as capable as the 28S. Everything else is the same. Neither one is very I/O capable though.

I like this series, especially because of their "right there" alpha keyboard. But they are fragile (especially that battery door opening...be gentle opening it; they are designed to chip and crack!) and the display isn't very high contrast. The size / form / LCD character font I like a lot better than the 48 series.

[Maximilian Hohmann]

Hello!

(06-21-2018 12:31 PM)mdunn Wrote:  2. The 28 seems to be the cheapest "serious" HP calc ... Is it because it's such an unusual machine?

I haven't got to the programming section yet, so those are just first impressions.

Wait till you are at the programming section and then you will know why people sell it so cheap. If I wouldn't have mine for the sake of a complete collection I would actually pay someone to get it as far away from me as possible (that would be New Zealand I guess) ;-) There are two kinds of humans: Those who love RPL (the "programming language" used in these calculators) and those who detest it. There is nothing in between...

But I actually like the clamshell design and the proper alpha keyboard of these calculators. If only they would have used BASIC as programming language!

Regards
Max

[rprosperi]

(06-21-2018 12:48 PM)Thomas Okken Wrote:  The main drawback of the 28, and probably the reason why they tend to sell for cheap, is the lack of external storage.

Though lack of I/O (well, I anyhow, I guess IR printing must qualify as O) is a big limitation, I think the larger reason these machines are not too popular and relatively cheap, is the terrible battery door/door frame design.

Almost every Champion series machine that has actually been used a lot has a broken or cracked battery door, or more often, the door frame. This is due to the aging plastic becoming brittle and the continuous strong pressure exerted against the door by the battery springs. Be VERY careful when removing and inserting the door - use your fingers to depress the batteries when moving the door along the small channels in the frame that the metal edges slide within.

Oddly, the business series Champion machines (18C, 19B and 19BII) seem to have this damage less often than the 28C/28S; perhaps this is because Business machines are used less and/or treated better. As a result, these often go for higher prices than the Scientific machines. If you plan to buy any Champion machine from eBay, etc. be sure to ask seller about door/frame condition and ask for photos of that area. If damaged, you will be able to see the cracks or chipped edges, and sometimes it just looks like the door is installed but bulging out. An undamaged door/frame will appear smooth and barely visible thin crack along the door edges.

Late production of the 19BII changed to a totally different battery bay design, with a door on the back of the machine that is not subject to the battery spring pressure. These are much nicer, but are also accordingly more expensive.

IMHO, this is the worst battery bay design of all HP machines, as basically all examples will degrade in use over time.

[Thomas Okken]

(06-21-2018 01:43 PM)Maximilian Hohmann Wrote:  There are two kinds of humans: Those who love RPL (the "programming language" used in these calculators) and those who detest it. There is nothing in between...

Sure there is. I, for one, generally prefer RPN over RPL, but some algorithms are just a lot easier to implement in RPL, thanks to its local variables, support for recursion, and such.

(06-21-2018 01:51 PM)rprosperi Wrote:  Though lack of I/O (well, I anyhow, I guess IR printing must qualify as O) is a big limitation, I think the larger reason these machines are not too popular and relatively cheap, is the terrible battery door/door frame design.

Right, the battery door, I forgot about that. I didn't own my 28S long enough for it to break, but I remember that changing the batteries in that machine was a real struggle, so bad it made me wonder what idiot came up with that design (though I think it might actually have been OK if only the spring wasn't so terribly stiff).

Another issue was the hinge, wasn't it? I've heard that the flex cable, that runs through that hinge to connect the left keyboard to the main board, sometimes fails... and even if it doesn't, the hinged design makes the machine borderline unusable hand-held.

I guess those factors do matter more than the lack of external storage, particularly given how popular the 42S is, which has no external storage either.

[Maximilian Hohmann]

(06-21-2018 03:08 PM)Thomas Okken Wrote:  Another issue was the hinge, wasn't it? I've heard that the flex cable, that runs through that hinge to connect the left keyboard to the main board, sometimes fails...

I have a dozen or so of these various clamshell HPs (one of each model and some spares) in various states of deterioration, from new-in-box to heavily used, but apart from cracks around the battery door none of them has any serious problem. Not with the hinge and not with the display either - as opposed to some 48 series that I have.

(06-21-2018 03:08 PM)Thomas Okken Wrote:  ... and even if it doesn't, the hinged design makes the machine borderline unusable hand-held.

But only for programming where the alpha keyboard is really required. One can use these as normal handheld calculators perfectly well by folding the left half all the way back. For some time I carried around an HP19 as my daily calculator and didn't find it any different to "normal" calculators in that respect. And closing it resulted in a "naturally protected" device with no need for a pouch or case.

[BartDB]

I like the 28 series. My first HP calculator was a 28C, later a 28S.

I am one of the users that really likes RPL programming, compared to RPN (or keystroke) programmming, it has better loop structures and IF and CASE statements. It is also fully interactive with the stack (which the Basic-like HP Prime programming isn't).

As the RPL calculator was my first HP it's probably a case of what you started with is your favourite

I mainly use my calculator on a desk, so the fold-open design was never a problem for me. When closed it's self protected and fits in any bag/briefcase and all my programs & formulas are with me.

As said before, the 28S is more popular than the 28C.

Biggest let down for this calculator is the battery door. Be very careful with it!

-Bart

[grsbanks]

(06-21-2018 06:18 PM)BartDB Wrote:  Biggest let down for this calculator is the battery door. Be very careful with it!

Very true.

Sometimes, however, you strike lucky

http://www.hpmuseum.org/forum/thread-9705.html

[mdunn]

Thanks for the many opinions on the 28. Yes, I very definitely got the 28S, and also lucked out on great overall condition, including the door. Perhaps someone added the foam strip in the battery compartment to reduce total outward pressure on the door (or maybe that was a late HP "fix"). The downside being, those two cells could get pushed in too far, and not make door contact at all. When I said I had to whack the calc to get those two out, against my leg works. It doesn't have to be on something hard!

Love/hate...yeah, I get it. I think I will end up somewhere in-between though. It's not like I expect to be doing anything serious with it...

[ijabbott]

(06-22-2018 03:49 PM)mdunn Wrote:  When I said I had to whack the calc to get those two out, against my leg works. It doesn't have to be on something hard!

I bet you have the bruises to prove it!

[jebem]

(06-21-2018 12:31 PM)mdunn Wrote:  1. Is the 2-cell tube supposed to be so tight? I really have to whack the calculator to get the cells out.

The original battery on the side model can hold the battery cells inside in such a way that I need to rock the calculator a little to convince them to slide and go out.

I have 6 of these machines among 19's and 28's, and all exhibit this behavior, even for one 19BII that has the battery on the back.

I found out the cause for this to be related to the fact that there are N cells with slightly different sizes depending on the brand.
Here: http://www.hpmuseum.org/forum/thread-107...l#pid97721