From pfund@uni2a.unige.ch (Daniel `HB9VBC' Pfund)
Newsgroups: comp.sys.hp48
Subject: HP48G memory upgrade DOES work... just find the correct place!
Date: Tue, 16 May 1995 14:47:35 GMT

Get the file in the /dist/hp48g/docs that describes some other stuff
first!!!!

Disclaimer
**********

Do this modif at your own risk!  You MUST know how to de/solder
before attempting this.  Your HP48G is all in SMD technology.

Also, please read the doc describing how to open your calculator and which
describes it's internals.



Here's what I did to upgrade my HP48G's memory to 256k:

1)Unsolder the 32k smd RAM chip.

2)Solder  a  128k  smd  in  place, the extras pin solder points are already
there.   The  HP48G  automatically  recognizes the 128k.  If you stop here,
you'll just have 128k RAM (acts like aGX).

3)Solder an 74HC00 smd in the spot at the bottom right if you have the
battery case at the bottom and screen facing the table.  It is next to the
black electrolytic capacity (1000 microF).  This is the place I first
couldn't find... but it's easy once you saw it!  ;-)

4)Solder another 128k chip onto the first one (piggy-back), not easy
because the pins are not really long enough... but you can manage it!
Leave the pins 22,24, and 30 up; these go:
	RAM		Connector
_CE1	22	-	40	GND
_OE	24	-	22	_OE
CE2	30	-	21	CE

5)Connect these pins from the connector:
_Write Protect	37	-	VCC (on electrolytic capacity)
card present	38	-	VCC
card type	39	-	GND (to indicate RAM)

6)Solder a 1MOhm resistor between pin 2 of connector to VCC in order to
indicate a good working ``battery''.


That's it, you get 128k base ram and another 128 in a port (1 or 2
depending if you soldered the wire on the back or front pin of connector)
which you can merge together or leave seperate.

If you have further questions, do not hesitate to contact me.

Regards,

Daniel PFUND

-- 
    __
   /// Daniel Pfund                       Internet: pfund@uni2a.unige.ch
__///  University of Geneva, Economics   AX25: hb9vbc@hb9iap.srom.che.eu
\\\/   meet the AMIGA's little brother: the Psion 3a! \ham radio amateur

[Rem by DOEGOX: I did it with 3 smd! but it's true it's a hard job!
Only if you can find only smd versions of 128k ram]

