TRS-80 Model-100 24K Memory Upgrade
OK, this is a little tricky, and it requires some expertise, but if you darebeing bold it will give you a lot of satisfaction as it did to me a few years ago.
At the time I owned a TRS80-100 with 8K ram and did not want to spend the money to buy the original chips for the memory upgrade.
On the other hand I had several 6264LP in my lab, and I decided to use them up. (LP stands for LowPower!)
I just found the schematics, and you have to forgive me if you'll have to fill in the blanks, but I am myself trying to put it all back together as I write.
To begin, the TRS80-100 should have 3 empty sockets for the original chips.
Each original chip had 4 2K Static Ram modules that are enabled by CE1.CE2.CE3.CE4 for a total of 8K.
The 3 sockets are connected pin by pin, except for the CE pins that obviously come from different outputs of the memory decoder.
The yellow pinout represents each socket as it is on the M-100.
Because the 6264LP chip is a single 8K bank, it does not require 4 separate chip select, but just one (CS1), while CS2 is used to put the chip into stand by mode.
Most of the pins between the socket and the 6264LP are compatible, but not all.

A12   WE
 A7  A7  1

 28 VB CS2
A6 A6     A8 A8
A5  A5      A9 A9
A4  A4    >>  WE A11
A3  A3    >>  CE4 OE
A2  A2      A10 A10
A1  A1    >>  OE  CS1
A0  A0       D7  D7
D0  D0       D6  D6
D1  D1       D5  D5
D2  D2       D4  D4
GND  GND       D3  D3


CE1       GND  
CE2   14  15  CE3
It is first necessary to "open out" the "incompatible" pins of the 6264LP. With this I mean, bend those pins 90 degrees so that they "stick out" instead of being parallel to the other ones. The procedure is simple and harmless to the chip if done just once.
Now the chip can be inserted in the socket
To reach the full 32K capacity, 3 chips 6264LP should be mounted: one for each socket. Now we need to complete the connections.
A11 and A12 need to be wired to each 6264LP from the motherboard; best shot is to do it from M3 or M4 (40H138 pins 1 & 2). So use very thin insulated wire (like the type use for wire wrapping) to connect the following:

 23 (A11)  M3 1
 2 (A12)  M3 2
 27 (WR) Socket 25 (WE)
 22 (OE) Socket 22 (RamRst)
 28 (VCC)  Socket 28 (VB)
 26 (CS2)  M3 16 (VDD)
At last, we need to install the "new" memory address decoder, a 74HC138 or 40H138 to provide the CS1 to each 6264LP. For convenience, you can solder it "on top" of M3 or M4 by opening up all pins except for 8 and 16 which will connect to the power directly from the chip below.
Signals A13,A14, and A15 can be wired from the system bus connector or from M16/M17.
Because the standard RAM is located at the top of the 64K, it "would" be activated when Y7 becomes active (low). We don't need to use this signal because the standard Ram is already addressed and enabled on the mother board. On the other hand, we'll use Y6, Y5 and Y4 to enable the 3 additional chips (or less) that we have added.

A13 A0 1 16 VCC  VDD
A14 A1 2 15 Y0  
A15 A2 3 14 Y1  
GND G2A 4 13 Y2  
GND G2B 5 12 Y3  
VDD G1 6 11 Y4  to CS1-1
Y7 7 10 Y5  to CS1-2
GND GND 8 9 Y6  to CS1-3


I have built this myself a few years ago and had no trouble with the computer since. I recommend to take out all batteries, turn off the memory backup battery, and use a small power grounded soldering tool for the wiring. Unfortunatelly, I have sold the unit that was modified, and I don't have a picture of what it looks like after the "surgery".
Good luck, and feel free to Email me for any help I can give you about this project.