HP-75 RAM expansion?

[Paul Berger (Canada)]

(04-21-2017 01:24 PM)Martin Hepperle Wrote:  

(10-13-2016 12:13 PM)Martin Hepperle Wrote:  ...
In fact, after reading said article (or was it a nightmare while I slept?) I bought six (4+2 just-in-case) TOSHIBA TC5516AP 2048x8 BIT CMOS Static RAMs and now I cannot locate the article anymore...
..

Finally! After searching day and night since October 2016 for this article I finally found it again. Now I can sleep better.
The article appeared in the Jan/Feb 1984 Computer Journal of PPC on page 21. It does not show up in the table of contents because it is disguised a letter from a reader.
It describes how to implant four 2K 5516 RAM chips into the HP 75 to spare the cost of a 8K RAM module. While the soldering in piggyback fashion would be easy, one would have to mill out part of the case to make the chips fit (or one could machine the DIL cases thinner, but that's more for the explorer type).

Martin

If you got the chips in a SOIC package you could probably easily work something up that plugs into the connector for the 8K expansion, unlike other edge connectors in the 75 it is a standard 0.1 pitch edge connector. You can use almost any 2K SRAM chip the 5516 was the part number Toshiba used but 6116 is a more common designation. I had some trouble tracking down 2Kx8 SRAMs in SOIC package to repair a couple 8K modules but ended up getting about 25 when I finally tracked down a source. You could also use a single 8K SRAM but you would need a little extra logic to re-encode the 4 chip selects into the top two address lines and chip select.

Paul.