HP 75 Expansion Pod

[Michael Fehlhammer]

Recently I acquired an HP 75 expansion pod that exhibits strange behaviour:
After a reset ( INITIALIZE ) of the electronic disk, XMEM shows only 24436 Bytes available. I know there are two versions of expansion pods, featuring 32K and 64K of electronic disk space, respectively. But 24K ??
There is not much file system overhead, a 64K pod shows 65492 Bytes free when executing XMEM.
Serial number is 2419A00008. Maybe a prototype?
Or is the memory organized in 4 banks, and one might be damaged?

Is it possible to upgrade a 32K pod to a 64K pod ( or even larger ) easily?

[Paul Berger (Canada)]

The memory inside the POD is 8K SRAMs and it would seem it auto-configures so yes it is possible that you have a bad chip or perhaps it was only populated with 3 SRAMs. You can upgrade then, I upgraded two of the three I have, but it will depend on your soldering skill. The SRAMs are in 28 pin SOP package, and upgrading is just a matter of populating the remaining SRAMs. It may be possible for it to be larger, however there is only pads on the board for 8 SRAMs, and the logic driving the chips is buried in a custom chip. It is possible that there may be technical information available, but I have never seen nor heard of it. I do have suitable 8K SRAMs that have been desoldered if you have trouble finding parts. When taking apart the POD be careful of the cable from the connector to the circuit board inside it is just a flexible circuit board.

[Michael Fehlhammer]

Hello Paul,
thank you for these tips! Really good news that upgrading to 64K is possible. I am not eperienced in soldering, but I know a person who might to the job. The 8K SRAM chips shouldn't be that difficult to find, anyway, thanks for your offer!