I N T E R N A L R A M I N S T A L L A T I O N By Kenn Becker June 19,1986 In this article I will tell you how I improved the internal memory of my Model 100. I am in no way advocating any particular equipment or process, merely documenting my method for a permanently installed RAM bank. Back in November 1984 I bought a used PG Design Electronics 32K expansion RAM bank, #000132, from Rick Mendosa, who could no longer use it because its backup battery holder occupied the ROM socket space [and because he had purchased a 64K expansion RAM bank]. I was not too thrilled about having to deal with the backup batteries or extending the 40 pin bus, so I bought the RAM with a permanent installation in mind. The first thing I did after buying the chip assembly was to open up the Model 100 and look for a suitable home. There is very little room inside for the RAM bank with the exception of the space right above the expansion bus and ROM socket compartment, where it is almost a perfect fit. In preparation for insertion several tasks were performed: A: I prepared approximately 31 very fine insulated wires for the electrical connections. B: At this point I made sure that myself and the soldering iron and my work surface were properly grounded so as to minimize any possible damage to the CMOS junctions used in these computer components. C: With fine wire cutters I clipped off all of the gold plated bus pins on the RAM bank. Otherwise they would poke into the underside of the keyboard when assembled. D: The battery box was completely removed from the bank using a fine soldering iron. Before its complete removal I noted the battery polarity on the bank with a sharp pencil. I then soldered two fine wires to the battery terminals. E: Each prepared wire was then soldered to each land where a pin had been snipped off. To prepare the Model 100 I first saved all files I didn't wish to loose, then I removed the AC adaptor and a battery from the battery box and turned off the memory backup power switch on the bottom. I then soldered each wire from the RAM bank to its corresponding pin socket land on the component side of the Model 100's main printed circuit board. I very carefully used as an aid the existing pin numbering standard so as to not confuse the wires. Using the technical reference manual, I located the factory RAM battery backup connections and using the proper polarity, I soldered the previously installed back-up wires from the RAM bank to the Model 100. Once all the connections were double checked and tested, I then fired up the computer and loaded the bank switching program. This was done prior to the final installation of the bank into the computer. There were no problems in the operation of the soldered in RAM bank, so again I disconnected all power to the computer and proceeded with the physical installation of the RAM bank. The most difficult part of the process was insulating the various parts of the RAM bank from the inside circuitry. The bank lays on its back saddled between the factory-installed RAM chip on the left and the system ROM on the right. Because some of the chips on the bank lie directly on top of the factory RAM, a strip of insulating tape was placed on it which extended all the way to the ROM chip on the right. The middle area was also insulated with Fish paper to keep the back of the 40 pin bus from shorting through the insulating tape. Double stick tape held the bank in place. The top of the bank (clipped pins up) needed several layers of plastic tape over all exposed circuitry and an extra insulator over the clipped bus pins, because all of these areas make intimate contact with the bottom of the key circuit board, especially when you hammer on the keyboard like I sometimes do in frustration. It is a tight fit when fully insulated, but the bank does help support the keyboard when together to give it a more solid feel. The spacebar guide-post sleeve needed to be trimmed to facilitate the spacebar's usual smooth action. None of the other keys were affected. Once the bank was installed over a year ago, I have paid no attention to it on a hardware level. This is because its backup power is taken from the factory RAM backup NiCad. At the 40 pin bus the only power available is switched off when the computer is turned off; this is not suitable for RAM backup unless it charges a NiCad pack with the RAM bank. That is a great idea as long as the computer is turned on occasionally to recharge the battery. The rule of thumb is: with nothing connected to it, a NiCad battery looses 1% of its charge per day or approximatly 1/3 of its total charge in one month. My point is the internal RAM backup NiCad in the Model 100 is constantly being trickle charged from the main power batteries or the AC adaptor, so if all your RAM is connected to the single backup battery you only have worry about one system. The last thing to install in the computer is the bank switching routine. I gave it a very short name and hid the file for security; whenever I want to access the bank I just type in the name. The bank select routine in the bank has the same name to exit, although you may exit by turning off the power from its main menu. If you crash in the bank, turning off the main power and then back on will get you back to the main menu where you can type in the bank switching program name and before you hit ENTER you hold the CTRL key and the BREAK key down simultainously while hitting enter. You will then have entered a cold-started but unjammed RAM bank. If you cold start the main RAM, your bank will hold its memory as long as you don't needlessly turn off the memory power switch. You will need to type in your bank access program to get in to the bank. Since in my Model 100 the bank is permanent, I attached a copy of the switching program to the inside of my battery cover. I see the possibilities of permenantly installing 96k of RAM inside the Model 100 and plugging in to the 40 pin bus another 96k. Add in the initial 32k of RAM for a total of 224k of RAM in 6 banks plus the main. If you are interested in permanently installing your RAM bank leaving your accessory port completely empty, you may call me, Kenn Becker, at "CAM-X Camera Service" (805) 966-7121.