PUBLISHED IN LIMA NEWSLETTER OCTOBER 1987
 
 
        INSTALLING EXTENDED BASIC INSIDE YOUR CONSOLE 
 
                      by John F. Willforth 
                        West Penn 99'ers
 
(Ed. Note:  This article is reprinted from the July 87
issue of the newsletter of the West Penn 99'er Club.  It
has been our own experience that cleaning the console,
particularly the cartridge port will usually solve problems
encountered when using the XB module.  Instructions for
doing this were publisned in the Jan 87 issue of Bits Bytes
& Pixels.  It has also been our experience that a GRAM
KRACKER with its gold plated contacts will often run
extended basic reliably.) 
 
    For many of us there has been much frustation over the
last several years about "HANG-UPS" that occur to the TI
99/4A using extended basic, just as the most critical part
of a program or game is reached.   There are those who
would lead you to believe that the power supply has been
the cu;prit in the majority of the console locking in their
club.  This may have been the problem experienced in the
microcasm they are in.  I have experienced the problems
with inconsistent and noisy D.C. voltages issued from the
TI supplies also.  A few months ago I ran through 5
straight VDP memory problems in a row, and could have made
the statement that most if not all TI console problems will
be found to have defective 4116 dynamic RAM chips.  This
would have been absurd!  I'm making this statement only to
try to reassure you that of all possible causes for console
hangs, the GROM connection/cartridge connection is far and
away the most common, and in particular the mating (or lack
of) between the Extended Basic and Grom Connection, is the
greatest culprit.  The purpose of this article is to assist
those of you who would like to mive the Extended Basic
module on board. 
-----DO THE FOLLOWING AT YOUR OWN RISK! 
 
PARTS; * 1' ribbon cable (36 lead) or 2 lengths of 25 lead
              cable. 
       * 1 Extended Basic module (shell removed) 
       * 1 double pole single throw slide switch (for
              enabling/disabling Extended Basic) 
       * Solder iron, wire cutters, etc. 
 
    I'm not going to get into the details for I feel if by
now that you can't remove your own CPU from your console,
you shouldn't be attempting this.  Get someone who can.
remove the GROM Connector from the unit, and attach the
ribbon cable to the pins of the rear of the circuit card
that the GROM connector is attached.  Attach all but pins 4
and 6 to ribbon cable.  4 and 6 are unused here.  Now,
keeping the length of the wire to less than 8" attach the
other ends of the corresponding wire to the Extended Basic
card edge connector leads, remembering the relationship
between the two.  i.e. pin 1 must go to pin 1, 2 to pin 2,
and so on (not 4 or 6).  before you attempt any further
modification to the machine, reassemble and see if Extended
Basic comes up on the menu, and still functions, SIZE,
ACCEPT AT, etc.  If you are still functional, continue. 
 
    Remove the 100 ohm resistor indicated, and cut the two
traces where shown.  Now you may solder 4 equal lengths of
wire to the switch (not longer than 10" in length).  Attach
two of the wires across the cut in the trace (x) and the
other two across (y), making sure that the pairs are on the
same switch pole set.  Now, test the results again. 
 
    If the Extended Basic works when the switch is closed,
and the cartridge slot will accept cartridges (meaning that
a variety of GROM/ROM cartridges will function), when the
switch is open, then you are almost home.  Mount the switch
in a convenient location and insulate the bottom of the
Extended Basic cartridge and locate the TOP RF SHIELD to
the left of the GROM connection.  Reassemble.  It would
also be of benifit to you at this time to install a reset
button across pin 6 of the CPU chip and ground.  Trust me. 
 
    The reset switch will be particularly useful, in that
you will now not be able to reset the machine by inserting
the Extended Basic cartridge.  You may find that without
the RESET switch, you will have to turn the console power
switch off and then on to begin operation after switching
from basic to Xbasic or other cartridges.  This is an easy
option to install with a momentary contact switch across
pin 6 on the CPU chip (TMS9900) and ground.  Reference the
first drawing. 
 
    The second drawing is here to help you find the two
traces that must be cut, and the 100 ohm resistor that must
be removed.  The drawing of the switch on the right of the
second drawing is to assist you in locating the switch
properly to the circuit.  Attach wire pairs across the
trace cuts.