UPGRADING THE C128 FROM 16K TO 64K OF VIDEO RAM 06-06-06.


           UPGRADING THE C128 FROM 16K TO 64K OF VIDEO RAM    06-06-06


There used to be an easy-to-install piggyback board made by Chip 
Level Designs (Lawrence Hiler) back in the 1980s. You would pull the VDC 
chip, install the board, then plug your chip into it. It had the upgraded
video RAM chips on it and required no soldering. Unfortunately, that board
has not been available for years. If you have the skills (or know someone 
who does), you may be able to make your own board using the info on my 
site. It shows the CLD PC board layout and photos of the parts used. 
It's at http://staff.washington.edu/rrcc/uwweb/C128/C128VRAM
     Upgrading the VRAM on your own involves unsoldering the two original 
4416 (16K X 4) RAM chips (probably marked something like: MB81416-12) 
inside the tin can in the middle of the motherboard. The two chips are at 
board locations U23 and U25 and are very likely soldered in. It's tight in
there and desoldering chips is a pain anyway, not to mention risky if you
accidently break a foil trace and don't repair it before installing the new
chips. You end up covering up your mistake rather well. As a tech, I always
desolder the original and put in a socket. That way, I have the option of
putting the old ones back if the upgrade doesn't work for some reason. You
never want to solder on the board more than once if you can help it.
Sockets are cheap. An alternative to desoldering the whole chip is to cut
off all the pins close to the body of the IC, then desolder each one and
clean out the holes with wick or a solder sucker so the new chip (or
socket) will fit. That's much easier on the board, but obviously destroys
the chips. Not a big deal... they usually end up in the garbage anyway. 
     So, you'll need two 4464 (64K X 4) RAM chips. Jameco Electronics @
1-800-831-4242 has them, but you'll need to add $5 for orders under $25,
then shipping on top of that. They have a WEBsite: www.jameco.com. The
Jameco part number for the chip is 41582 or 41574 or 41611. Those three
numbers represent the same chip, but at different speeds, 120ns, 100ns, and
80ns respectively. All will work and cost less than $3 each. Jameco has the
sockets too. Order # 38113 or 112230 socket (18 pin DIP single or double
contact) for less than $0.25 each.
     For desoldering, you'll want an iron of about 25 watts. Don't be
tempted to use your 30 year old soldering gun... it will eat that board.
Make sure you mount the new chips exactly the way the old ones came out.
There is a notch at one end so you shouldn't get them in backwards. Use a
marking pen to indicate where the notch goes if necessary. After the new
sockets/chips are installed, carefully inspect your work for solder
splashes or bridges between traces, etc. If all is well, put it all back
together.
     Power up the computer and observe the opening screen. You might notice
that just -before- it comes up, the screen looks different than it used to. 
When the opening screen appears, it should look the same as before. One way
to tell if you have the upgraded VRAM is with a little BASIC program typed
in 80 column mode: 
POKE DEC("D600"),28:POKE DEC("D601"),63:SYS DEC("FF62"):SCNCLR 
If the screen says: READY and looks normal, you have 64K of VRAM. If you
have only 16K, the screen will fill up with zeros. 

Ray Carlsen CET
Carlsen Electronics