From tw45639@vub.ac.be Wed 21 Jun 95 20:58:43 From: rbk3055@tam2000.tamu.edu (Brad Keef) Newsgroups: comp.sys.hp48 Subject: Here's a mail order source for 128k RAM chips Date: 18 Jun 1995 20:04:19 GMT Message-ID: <3s20s3$au3@news.tamu.edu> This upgrade information is NOT an ad for Jameco. They are one of many sources for 128k SRAM chips. I found their service to be fast and helpful. ******* ATTEMPTING THIS UPGRADE COULD DAMAGE YOUR HP48g ******* ******* Upgrade at your own risk. Don't do it unless you******* ******* really need the extra memory. ******* I just upgraded my HP48g from 32k to 256k by using the very well written instructions that are available @ nic.funet.fi in the directory /pub/misc/hp48g/uploads in the file 48gs256k.zip I used the 2nd section written by Thomas Otten that describes installing 2-128k SRAM chips by placing them (I used double-sided tape) on the circuit board above the expansion connectors. It works great. I think that a lot of people wonder where they can buy the 128k SRAM chips. Here is one location: Jameco Electronic Components & Computer Products 1344 Shoreway Road Belmont CA 94002 phone: 1-(800)-831-4242 2-Day delivery via UPS is $6. (upgraded from 3-day for free). 1st class US Postal delivery is also available. These are the part numbers and prices for the chips that I used to complete the 256k upgrade: _______________________________________________________________ Descrpition Their Part # Price ($) ------------------------- ------------- --------- 128k SRAM Lo-Power (85ns) 103982 $14.95 ea Quad 2-Input NAND Gate (14pin) 86060 $00.19 ea 30 Guage wire (100 ft min) 37006 $01.95 ea 1 Meg Ohm resistor (100 min) 107810 $01.39(per_100) _______________________________________________________________ The 1 meg Ohm resistor is available at Radio Shack, etc. It goes between Pin # 32 on the SRAM and pin # 28 on the 32k SRAM chip that is already installed. (I actually used a 2.2 Meg Ohm resistor because I had one on hand. It works fine. I think that it just needs to be greater than 1 Meg but not infinite???) The 128k SRAM is listed as a 628128LP-85 32-pin 128KB*8 85ns Lo-Power CMOS. The SRAM actually comes delivered as a 681000LP DIP (Dual in-line package). It is exactly what you want for the upgrade ! (The 48gs256k.zip file states that this is the 128k chip in the HP48gx but the gx uses the much smaller Surface Mount version. The DIP is much easier to work with for the upgrade because of its larger size.) The Quad 2-Input NAND Gate (14pin) (really a 74HC00D) has to be soldered onto the empty 14 pin pad in the bottom, right corner of the circuit board nearest the battery case (below the Black Capacitor.) The chip that I got from Jameco is a Phillips 74HC00D. It works Great! It has a white line across one end. Put this end towards the capacitor!!!!! This is tricky because it is in a surface mount package (like micro-surgery???) so take your time. It's best to have some solder-wick available to undo any mistakes. Don't worry too much about shorting 2 pads together. Just use a very small amount of solder. You can use the solder-wick to "suck up" any excess solder. A multimeter is great for checking to see if you have accidently shorted 2 pads together. There should be an OPEN circuit between each pad (infinite resistance) If the pads are shorted, just use the wick and try again. LOTS of patience. I used 30 guage wire for the upgrade and it is small enough to do the trick. It takes a few hours to wire everything. (I'm slooooow) I did strap (short, connect, etc.) the tip of my WP40P Weller soldering iron to the negative tray on the HP to keep everything at the same potential. (My iron has 50 VAC between the tip and ground.) Take your time opening the case. Go especially slowly when peeling off the face plate. That is the most difficult part of the HP to return to a new appearance. I followed the instructions in the 48gs256k.zip file and had no problems. It was nice to see 128k of RAM available when I finished the upgrade use the command (<-, memory, [mem]). I merged my port 1 with port 0 to get 256k of useful RAM in port 0 (actually 258889.5) Use the command (<-, library, [merge]). It's on top of page 28-16 of the users guide. I completely removed the shield inside of my HP. I don't necessarily recommend this to other people but I have found it to cause no problems so far. I now have no speaker and have to open the case to RESET the calculator (hopefully I'll never do this). If after the upgrade, your HP is locked-up, remember that the reset button is under the upper,right, rubber foot. Pull off the foot and use a paper clip to reset. The only other thing that I had to do was glue a piece of plastic to the metal plate (negative terminal) below the positive battery terminal. This prevents the batteries( + and - ) from shorting out and overheating/melting your battery case. This may not be a problem for people who leave their shield on place and only cut a hole in it to make room for the new RAM sandwich on the circuit board. I would recommend leaving the shield in place. Make enough for the new RAM. Good Luck. The fate of your HP is in your hands. e-mail: rbk3055@tam2000.tamu.edu (Brad Keef)