channelmaniac:
TIP: Installing a "no title delay" BIOS

One of the popular mods for a Colecovision system is to replace the 4764 type BIOS chip with a replacement EPROM programmed with the "no title delay" custom BIOS chip. This can be done one of 2 ways.

1. Use a 24 pin 8k x 8 replacement EPROM such as a Motorola 68764 or 68766. This is a difficult to find and expensive chip.
2. Use a 2764 EPROM, a JEDEC standard EPROM which is cheap and easy to find.

Option 1 gives a direct drop in replacement while Option 2 requires some modifications to be done to the board.

The Colecovision board has a 24 pin BIOS chip in place but has holes for the standard 28 pin chip. The problem is that the 28 pin jack isn't wired properly. To use the 2764 chip a bit of board modification will have to be done. 

First, desolder and remove the old BIOS chip. Next, desolder the holes for jumpers WJ4 and WJ5. These jumpers are located right next to the BIOS chip. Flip the board over and look at the desoldered holes for WJ5. Off each end of the jumper location (which is empty by default) WJ5 are little round cut-out pads connecting to other solder points. Cut these out. There's one between one end of WJ4 and WJ5 jumpers and another one that comes off of WJ4 and connects to pin 2 of the 28 pin socket location (Just left of pin 1 of the 4764 BIOS chip.)

With those 2 pads cut the next step is to solder in jumpers at location WJ4 and WJ5. The board is now wired for a 2764 EPROM.

Solder in a socket, program the proper code into the EPROM and insert it. Give the board a smoke test. If it's not working, trace the signals and double check your work.

Pin 2 is A12
Pin 23 is A11
Pin 20 is CE*

If A12 and A11 are shorted then you didn't cut the circular pad off one end of WJ4. 

If A11 and CE* are shorted then you didn't cut the circular pad between WJ4 and WJ5

Once working... Congrats!