When Commodore released the PET 40xx and 80xx series they introduced a Universal motherboard that could be used in either computer. If you have a 40xx PET with a 12" CRT display (Known as the "Fat 40") you should have one of these boards. There are 2 versions of this board and in this article I am covering the upgrade for a Universal Board 2 (revised Universal Board). The 2 boards are very similar and using the information found here you should be able to upgrade the original Universal Board. The ROM provided here for use with the N keyboard (Graphics keyboard) will work with either board.

Background:
After determining that I had a Fat 40 I went on the search for information about upgrading them. Here are the sources I used in researching this article:

TPUG Toronto Pet Users Group - Information for upgrading the original Universal board appeared in TORPET issues 7 (October 1981), 8 (January 1982) and 11 (June 1982). Those issues and more are available in the Archives section of the site.

Universal Board 2 Schematic- 8032090-7.gif shows the board and jumper layout for the board used in this article.

Universal Board Schematic - 8032080-7.gif is the board and jumper layout for the original Universal Board.

Vintage Computer Forum - Always a place to get helpful information and discuss classic computers.

The Upgrade:


Upgrading took about 2 hours with interruptions. The time involved entirely depends on the tools used. If you use a desoldering station as I did then it should go quickly. Using other desoldering methods could take longer.

Parts Needed:
2 - 74LS244 for UB6 and UB7
2 - 2114 SRAM chips for UC6 and UC7
1 - 74LS373 for UB8
1 - 2516 or equivalent EPROM.

Optional Parts:
3 - 20 pin low profile IC sockets.
2 - 18 pin low profile IC sockets.
1 - 24 pin wide low profile socket if needed.

I started by removing the board from the PET and desoldering all the holes and jumper wires (leaving them in the board). Once the board was clean of solder I moved the jumpers to the new locations:

The jumpers in the middle of the board (highlighted in CYAN) all need to be shifted up one.


In the lower right of the board (highlighted in ORANGE) one jumper needs to be moved from the 40 column to the 80 column position. The jumpers below (labeled Y and Z) are for setting 16k and 32k RAM size (pictured in the 32k position). If you are taking the opportunity to upgrade RAM also you need to move this jumper to Z.


The last set of jumpers are located near the lower center of the board (highlighted in YELLOW). These need to be move to 5 and 8. Note 8 (green wire) on the Universal Board 2 jumps OVER the 2 pads in the middle. This was a point of confusion for me as the .gif file showing the layout doesn't make it clear.


Once the jumpers were installed I soldered them and the sockets needed to hold the chips on the board. The sockets (or chips) need to be placed in the lower middle of the board (highlighted in RED). Although sockets are optional I highly recommend them. I then installed the TTL and SRAM chips.


My original edit ROM (UD7) was socketed if yours isn't socketed then you will have the additional work of dosoldering and installing a socket for the new EPROM. I used an EPROM adapter to hold a 2764 EPROM as I don't have any 2516 or 2716 EPROMs I can use. You should be able to make any adapter you may need by doing a search in your favorite search engine for building instructions.

PET 80 Column Graphics Keyboard Editor ROM - The new ROM needed for using the graphics keyboard in 80 columns.


When you power up the upgraded PET it will be in lower case mode (as is the standard 8032). You may need to make minor adjustments to the monitor (HEIGHT) which is accessible through the bottom of the monitor board.