[Coco] Teletex Cartridge Modification Procedure - Please Check for Accuracy

[Kip Koon]

Hey Guys,

Please check the following procedure for modifying a cartridge pak to
include an eprom chip and a switch to select which chip to use.

 

Please double check this procedure before you actually modify your cartridge
pak.  And of course all modifications to your cartridge pak WILL VOID its
warranty.  J  Now with that disclaimer out of the way, on with the fun!  J
The following procedure assumes the teletex chip rom has 28 pins.  If it has
a different number of pins, holler and we will help you in that case.  I've
never seen a teletex  rom, so I don't know.

1.       You desolder the chip enable pin 20 on the existing rom in the
cartridge pak.  This is an industry standard as far as I've seen while doing
research on ram, rom and eprom chips for my 6809 computer.

2.       Mount a single pole double throw switch into the cartridge case.
Use the break before make kind ideally, but of course the power will NOT be
on when you use the switch, will it?.  

3.       Solder the pad on the motherboard where pin 20 came out of to the
middle leg (common leg) of the switch.  

4.       Solder the  chip enable pin (now sticking straight out) of the
existing chip to one side of the switch.

5.       Take the 28 pin socket in your hands and bend straight out pin 20,
the chip enable pin for the 2764 8k x 8 eprom.  

6.       Now solder the 28-pin socket to the top of the rom chip with that
chip enable pin 20 still sticking straight out.  Make sure to orient pin 1
on the existing chip to pin 1 on the socket.

7.       Make all other needed solder connections to pins 1-19, 21-28 on the
socket.  This leaves you with the possibility of changing out/upgrading the
eprom chip with future versions.

8.       Solder the socket's pin 20 to the other side of the switch.

9.       Now insert the desired 2764 8k x 8 eprom with the cartridge pak
program of your choice which in this case is the HDB-DOS v1.3 DW3 eprom.

10.   NEVER FLIP THE SWITCH WITH THE TELETEX/HDB-DOS V1.3 DW3 DISK BASIC
CARTRIDGE INSERTED INTO THE COLOR COMPUTER AND NEVER WITH THE POWER ON!!!!!!

Now,  with this setup, you can have your cake and eat it too as they say!
Teletex or HDB-DOS v1.3 DW3 both individually available at your service
whenever you need them.  J  Nice, huh!

Oh by the way, pin 27 the A14 addressing line does not exist on a 2764
eprom, so that procedure is not necessary.  If you ever need to install a
27128 eprom in this modified cartridge pak, then there is more to do which I
will go into should that capability be needed also.  Have fun!

Kip