16K to 64K VRAM UPGRADE "PIGGYBACK" BOARD FOR THE C128
                     latest information 6-5-2011

     Ordinarily, to upgrade the video (RGB) RAM in the C128, you would
remove (desolder) the two original 16K RAM IC's (generic 4416 inside
the metal can on the 128 motherboard) and replace them with 64K (4464) 
chips. That would be difficult for most people to do themselves. An 
easier way was produced using a small plug-in board that anyone could 
install themselves. That board was built by Chip Level Designs back in 
the late 1980s and, unfortunately, is no longer available. To install 
that upgrade board, the original RGB chip was removed, the "piggyback" 
board inserted into the RGB socket, and the RGB chip installed in the 
piggyback board. The original RAM chips in the computer are then 
bypassed and do not need to be removed. If you ever come across one of 
those boards, it's easy to do THE VRAM upgrade in your C128 computer.    
     When this board is installed in a C128, the 4" X 6" metal cover 
that clamps over the RGB and VIC area will not fit back down all the 
way. The RGB chip sticks up higher because of the modification. As 
long as the metal "fingers" that touch the chips still do, the cover 
will work as intended as both a shield and a heat sink for those two 
chips. The metal shield that covers the motherboard will of course 
stick up a bit higher too. Just bend the fingers down a bit before 
installing it so all will be contacting their respective chips when 
the cover is reinstalled. 
     
     To those who might want to duplicate this board, I took some 
digital photos before and after I removed the components to show the 
board layout underneath them. There were two 4464 RAM chips and two 
24 pin sockets (the 8563 RGB chip is a 48 pin IC). The low profile 
socket pins stick through the 1/32" thick piggyback board far enough 
for the pins to be used as a header plug. Note the size of the holes 
in the bare board. The sockets used have a large round metal surface 
that protrudes out of the bottom about 1/32". Those stubs are what 
is soldered to the PC board. The pins that protrude from those stubs 
are what are plugged into the computer socket, and they are fragile! 
If any pins are bent, they will break off, and the socket must be 
replaced. Note that some of them are cut off because the RAM chips 
on the piggyback board bypass the ones on the computer motherboard. 
Pins 1 through 33, 37, and 43 through 48 are left intact. The ones 
removed are pins 34 through 36 and 38 through 42. The board holes 
are plated-through ensuring a connection from board top to bottom. 
The tiny surface-mount component on the back side of the board is a 
capacitor, a 0.022uF bypass filter across the supply line. Note the 
black dots I put on the bare board. Those indicate IC pin 1 for each 
of the chips.
     
     If I were going to build a board like this, I would change a few 
things to make fabricating the PC board easier. I would have the header 
pins offset from the IC socket so any low profile socket could be used. 
A single-sided board would require reconfiguring the layout and using 
jumpers, but it would eliminate the need to use plated-through holes. 
Header pins could be just bits of solid hookup wire soldered into the 
holes. Such wires would be flexible, and if accidently bent, could be 
straightened without breaking. If one or more did break off, they 
could be replaced easily. 

Ray Carlsen