Memory Upgrades:42s &48G

I am considering doing upgrades for the following two calculators. The 42s would be a simple 32 K RAM upgrade and the Hp48g would be either a 256K or a 512K RAM replacement upgrade. The 48G is fairly easy to Upgrade to 128K but since an Hp48G+ is readily available, it is not feasable to compete. (I would rather have a new calc with an Hp warranty, myself).

I do plan to provide a 30 warranty for the modification and either replace with another or restore with equalivent.

What do you guys think? Will it be worth it? I had a much easier time opening the 48G than I expected and does not show any mangleing that I have seen with other upgrades. However, whether I can do a 512K with a single chip or have to use two 128K chips will determine how worth while the project is.

To get to 128K is pretty straight forward (but as I said, not really worth it when you can get a 48G+). To get to 256K you have to piggy back another SRAM (not fun, and I would rather just land a 512 K RAM onto the pad instead of a 128K). But I am waiting on my 512K ram chip.

Any feedback?? I am listening.


I did two 256K upgrades to my 48G's. I piggy-backed one 128K chip on top of the other. (Most of the corresponding pins need to be connected above & below, with just a few unique chip-select signals.)

It worked O.K., until the piggy-backed chips started coming loose. As it turned out, simply bending the pins of the upper surface-mount chip down and soldering them to those below didn't last -- there was a slight gap, and a simple solder joint didn't seem to hold up very long. (And soldering individual tiny wires to connect each pin pair is for me nearly impossible to accomplish.)

I ended up backing 'em each down to 128K.

If I were to try again, I'd try some very fine bare copper wire, and "lash" the chips together, with figure-eight connections pin-for-pin, using one continuous strand (only for those pins that need to be connected, of course). Then, soldering the wire to the pins should be easy, and I would finish by cutting the crossover wires running over the top of the upper chip. (I haven't done this yet, but that's the idea.)

If I remember right, chip-select for 128K or 256K is fairly straightforward, but beyond that, there is extra logic required to generate the signals needed. Pay attention to chip-select logic, and look up all the references you can find. For my purposes, I decided 256K was as complicated as I wanted to go.


I suspected the 256K option is not pretty. I do not plan to use it since I feel the only way to get is to piggy back as you mentioned and then tie each leg individually, and I DONT have any plans to do so. This has been used to get to 640K on a 48GX and I didn't feel that was all that great considering, on a GX non Hp cards can be bought fairly reasonably (ie. a 1 Meg card from Klotz is about $60 vs a two 512K Ram chips are $36).

I am planning to make a single 512K RAM chip work, and realize I am going to have to use both inverter pads and probably run extra traces to chip from the inverter for bank selection.

Ideally, I will have 4 banks of 128K each, then merge 0 and 1 to form a 256K main memory, and two 128K banks of 3 & 4.


I just did a Google search on "hp 48g 512k upgrade" and found all kinds of stuff on this topic -- there's lots of good information available. (One article carries the upgrade to 4Mb!)

Do your research -- the chip select will have to be right for the thing to work, and most of the articles I've seen start from the already-upgraded 256K point and go on from there . . .


Sounds interesting- I've got a couple 48g's. I'd be really interested in banking and battery backup- the idea of a good on board backup for 256k is appealing.

Keep talking abotu this and I'll finally get around to cracking the 48s....


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