(c)1990 Golden Triangle, Inc. (c)1990 Wilson Van Alst All rights reserved. Fm: Stan Wong To: Paul Globman Paul (and James), I started out to build the budget banks project. Got most of it assembled but go so messed up that I had to scrap the whole thing. The hard part was hooking into pin 1 (+5V) of the option rom socket. I got to thinking that the regular 24K module gets it's power from the option ram socket. So I hauled out my data sheets and looked at the wiring diagram for the option ram socket. As near as I can figure out all I need to do is 1) clip pin 22 and wire it to pin 14. Exchange pins 1 and 27. Which is what I did. I plugged it in and it works. I don't know what the long-term implications are but can you explain why you have that complicated circuit between pin 20 of the IC and the socket? - 0 - Fm: Paul Globman To: Stan Wong Stan - What you did will work, but it will kill your batteries. Pin 20 of the chip is the chip enable (not) line, while pin 20 of the socket is bank select (not). The purpose of the transistor is to act like a switch, so when T200 power is off, the bank is not selected and when the T200 is on then pin 20 connects to the socket and allows the bank select gating circuit to determine if the chip should be enabled. Power to the option RAM is always available, but the 5v for the ROM goes off with power off. Failure to use the transistor circuit will result in both of the chips being enabled with power off, and will drain your AA cells quickly. Remember, the level CE/not means you need a voltage to unselect the chip. The 5v at pin 1 of the option ROM is turned on/off with POWER ON/OFF. That 5v at the base of the transistor makes the transistor a "switch", and when "off" there would be no voltage drop across the 4.7K resistor in the collector circuit. With no voltage drop, the Vbb at pin 28 is applied to pin 20 of the chip (deselects that bank when power is off). When the T200 is on and the transistor switch is "on" then pin 20 of the chip is effectively connected to pin 20 of the socket, via the emitter/collector path of the "on" transistor (allowing T200 circuitry to deselect the chip as required). - 0 - Fm: James Yi To: Stan Wong The transistor switch is supposed to pull up chip pin 20 High when the power goes down(0v on option rom pin 1).. When the 200 powers down, all the signal pins from the socket go Low - I at first didn't know that, so I just tied chip pin 20 directly to socket pin 20, and guess what happened - it's ok as long as the power is on, but when it powered down, pin 20 went Low, enabling the chip, causing the memory backup battery to drain faster - about three days to zip. - 0 - Fm: Stan Wong To: Paul Globman I understand your explanation of the circuit. After much studying I finally convinced myself that yours was the only practical solution. Congratulations for figuring it out. I built one bank, and tested it. The new bank kept crashing but I discovered a loose wire in the circuit. Now if works fine. Only I have to trust that my batteries aren't being drained too quickly. My main problem at first was getting to pin 1 of the option rom socket. I finally opened the machine up and soldered a wire to pin one on the pin side and snuck the wire next to the plastic clip that holds the memory board in place. All the resistors, wires, and transistor make a very ugly installation but at least it works. I need to go replace a transistor whose lead I broke and I'll be able to have a three bank machine! - 0 - Fm: Paul Globman To: Stan Wong Stan - James gets the credit for the original idea and the design of the transistor circuit. I wrote the article and tried to articulate the technicals to lay people, in an understandable manner. I have some background in electronics, so I had a pretty good understanding of the circuit just by looking at the schematic. And of course, YOUR knowledge of electronics helped make my explanation somewhat understandable. The actual components and resistor values are not "critical", and if you are a tinkerer, "approximate" components found in the "old parts" box could be used. - 0 - Fm: Stan Wong To: James Yi James, I finally convinced myself that the additional circuitry is really required unless ones machine lives on AC most of the time. I got bank #2 up and running. I'll get bank #3 going once I get replacement parts for the ones I broke. Since I have a supply of 32K chips sitting around thanks for developing the original idea and publishing it. It's saved my a lot of money in upgrading my "new" T200. - 0 - Fm: James Yi To: Stan Wong Somebody a while ago said that he experienced the Low Battery light coming on even when the computer is turned off, because of the connection to the printer... I wondered about how that might affect the transistor operation - the low voltage presented to the computer through the printer port could turn it on, pulling pin 20 low.. So in case someone wants to take up mass producing printed circuit board for it, this possibility should be checked out first.. I haven't used the transistor method long enough to be sure there aren't possible problems - I replaced the transistors and resistors with two small ICs, so I could access the unused 8K portions.. The 2 transistors and 4 resistors can be replaced with a single CMOS Quad NAND(or NOR) gates chip, and using a chip eliminates the possible problem caused by the printer port, since it doesn't need the connection to 5v pin.. - 0 - Fm: Stan Wong To: James Yi I don't leave a printer hooked up to any of my notebooks so it won't be a problem for me. Sounds like you've got some useful material for a Budget Banks Update Update. - 0 - Starting message #: 31121 Starting date: 05-Nov-90 21:23:43 Participants: Stan Wong 70346,1267 Paul Globman 72227,1661 James Yi 73327,1653