You already have a 128K ram HP. Let's go for 256K!
You have to solder the second chip above the first. Warning:
It's a hard work... Usually, the pins are a little too short to manage
an easy soldering. You have to solder these pins together with the help
of a tiny piece of wire...
All the pins have to be soldered on the first RAM except
3 of them: You have to bend up pins # 22, 24 and 30. They have to be connected
to some signals present at the place where the card connector is usually
soldered.
Take a look at the layout of the card connector
and also at the pinout of the rams.
The pins 2,21,37,38 and 39 of the card connector are devided for the two
card slots. For all those pins you have to use only the part of that pins
that has more distance from the battery case. This is the part for card
slot 1.
pin 22: connect it to pin 40 of the connector pin 24: " " 22 " pin 30: " " 21 "
There's some additional connections to do :
Here's the result: the same picture at high resolution
(232k)
Put now some adhesive tape on the metal shield to prevent shortcuts when
you'll close the HP. Close the HP, and ready for the first test!