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Hi guys,
Where can I get a 32 or 64KB RAM chip to upgrade my HP-42S machine?
I've been reading an article about how to do the upgrade job but I have no idea where to get the chip. I would apreciate if you guys tell me how to go about this.

Best Regards,


I use a chip called IS62C256-70U / SO28 made by Issi that I buy from a local electronics dealer. But there surely are several other options, just make sure that it is a 32 kilobyte, low power, 28 pin and in SO package.

Best regards,

Erik Ehrling

PS. Don't forget the Campaign for Emu42! (& Emu48 for Pocket PC)

Edited: 21 Aug 2004, 5:11 p.m.

Thanks, Erik,

I will look around to find a chip and try to do the upgrade myself.

Best Regards,

Try Cypress CY62256L-70SNC.

Digikey 428-1079-ND
$3.40 each, in stock at www.digikey.com

These work fine in the 42S.


I upgraded five HP42S so far. The one that's still with me (and one of the others) uses the 32KRAM chip removed from one old HP48G:

MT62C256F-70LL (by M?T... the mid character is a logo. a circle with a tic-tac-toe symbol inscripted on it)
The other one seems to have a different code, but I don't have it with me anymore.

The most interesting "origin" for these RAM chips is a PC-compatible sound board. It had three 32KRAM chips, and I used two of them so far. The third one I keep as a "spare", just in case. The code for these chips is:

W24257S-70L (by Winbond)

I am not sure this is a low-power RAM chip, but I have not noticed any reduction in battery life time. Unfortunately, I have none of these chips in working calculators so far. The fifth HP42S I upgraded has another chip with a different code, but I didn't find my notes about his one. Sorry!

I know new IC's are a far better choice, but in the case you have the source and are willing to try... Just keep in mind that it is always a good idea to test the chips before doing the "transplantation". Except for one of the units I upgraded (the first one, my own), all others needed to be opened and repaired somehow. So I took the chance to upgrade. Now that we're talking, I kept all of the 8KRAM chips in a safe place for whatever use later... and now they are, at least, five! Where in the h..l did I save them? Well, that's another history.

My 1ยข.

Luiz (Brazil)

Edited: 21 Aug 2004, 9:16 p.m.

Thank you Luiz,
I just ordered the chip from www.digikey.com, thanks to Randy info about. I will try not to destroy my almost brand new HP-42S during process.

Digikey part number: 428-1079-ND $3.40 each, in stock at www.digikey.com

Best Regards,


I ordered the chip at www.digikey.com. Thanks!
I will try to do the job my self on my almost new HP-42S.

Best Regards,