HP28S Case change



#6

Some time ago I broke my "old" HP28S' case near the battery holder when trying to remove this damn battery door. Now the whole thing seems fragile and will need some fixing.

So my question is : is it possible to transplant the innards of the 28S into another case, such as a 19BII ?
This sounds crazy, but based on the wizardry at work in this forum, who knows ?


#7

My son's HP-28S started coming apart a while ago. He'd been carrying it in his backpack, and thereby flexing it a lot.

When I finished pulling the thing apart, I found that the case is held together with an array of MANY little plastic pins, which are molded into one half, and fit into gripping sockets in the other.

I think the problem will be getting a good case apart without breaking off many of these pins. They seem to lock into the sockets tightly.

It could be that an undamaged case will come apart cleanly, as my experience is with one that already had many of the pins broken. But I'd say it looks doubtful.

Good luck -- maybe we'll hear from someone with a more positive experience!


#8

Why bother unless you already have a 19b. The (a used one of course) 28s sells for about the same as a used 19b. Therefore buy another 28s. They both sell for $50-80 used and in good shape on ebay. Also you could buy a 48g for even less and get more. A new 48G+ sells for less than $100 new and has a serial port and 4 times more memory and is a much better calc.

Paul has written many articles on calc repair and if he is doubtful of success, I would look to other answers before I would ruin a 19b to make a doubtful repair of a 28s. Buy a used 28s unless there is some really compelling reason (sentimental, historical) to keep this PATICULAR calc alive.

#9

My guess (without trying it) is that the 19B case and the 28S case are the same mouldings (albeit in different colours normally). The problem is actually getting the machines apart without
wrecking the cases.
HP heat-staked these machines together, and didn't intend them to be dismantled or repaired (thanks HP :-(). If you really want to take one
apart, peel off the overlays over the keyboards and above the display, and drill off the tops of the heat-staked studs.
Use a 3mm or so twist drill bit held in your fingers (or a large pin chuck), not in any kind of hand or electric drill. Do not drill too deep.
The machine will then come apart. You can then swap over case parts and either melt the ends of the studs with a soldering iron to keep it all together, or use
glue (epoxy resin, probably). But it won't be as strong as the original machine.
I've taken apart most series of HP calculators, and these are _the worst_ to get back together. With the later machines
(Pioneers, etc), you still have the heat-staked studs, but they just hold the back cover on. The machine will work if you just clip the back in place. With the Clamshells, the studs hold the keyboard together, they hold the
keyboard flexiprint against the logic board, and so on. It's essential to get at least some of them firmly staked for the machine to work at all.
Personally, I might try something like this, but only to show it can be done, not for a machine that I actually depended on.


#10

Please consider listening to the voice of experience! Tony obviously knows what he's talking about.

I didn't peel the overlay off the front of my unit, and it never occurred to me that those were all heat stakes. That would pretty much rule out any repair hopes, in my opinion.


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