     
           How to modify the PCjr to use Tandy 1000 graphics modes
     
    This mod will allow the use of Tandy 1000 16 color mode on a PCjr.  I
    can now run Flight Simulator 3 using the Tandy 1000 option.  Other
    programs that now work are Deluxe Paint 2 & Deskmate Software.  In
    general, any program which exhibits horizontal black stripes before
    this mod  will now run properly.  I have been running with this mod for
    several months with full Jr and Tandy support.  Deluxe Paint 2 reports
    "TGA not found  continue ?" Answer yes, then have fun.  THIS MOD HAS NO
    EFFECT ON ANY JR MODES.  ALL SOFTWARE THAT WORKED BEFORE THIS MOD WILL
    WORK AFTER THIS MOD.
     
     
                                    .------------------.
                                    |                  | **READ THIS**
                                    |   14           8 |
                                    |   ______________ | 74S86 Piggy
                                    |  I  74S86 PB on I| Backed on
                                    |  I] 74LS04 ZM33 I| top of 74LS04.
     .------------------------------'  I______________I| Pins 7 & 14
     |                                  1 2 3        7 | attached. All
     |                                  | | `----------' others lifted.
     |                     .------------' `------------. Pins 1,2,3
     |                     |                           | of 74S86 are
     |   16            9   |     20                11  | wired as shown
     |   ________________  |     ___________________   |
     |  I                I |    I                   I  |
     |  I]  74LS157 ZM31 I |    I]  74LS273 ZM30    I  |
     |  I________________I |    I___________________I  |
     |   1 2 3 4 5 6 7 8   |     1 2 3 4 5 6 7 8 9 10  |
     `-----* |             |                     *-----'
           * `-------------'                     *
           ******************//*******************     --- lines are
                             ^                         added wires.
                             |- cut this trace here    *** lines are
                                                       existing traces
            40                                     21
            _________________________________________
           I                                         I
           I]]]          8255 Chip  ZM22             I
           I]]]                                      I
           I_________________________________________I
            1                                      20
     
     
    Modification Steps
     1. Cut trace running from pin 2 of 74LS157 (ZM31) to pin 9 of
        74LS273 (ZM30).
     2. Piggy Back a 74S86 onto (ZM33) 74LS04.  Pins 7 & 14 are the only
        2 that need to be soldered to the 74LS04.  All other pins on the
        74S86 should be lifted level so as not to touch the 74LS04.
        BE SURE TO PROPERLY ALIGN THE CHIPS PIN TO PIN...
        THAT IS PIN 1 TO 1, etc...
     3. Add 3 wires...Use wire wrap 28 or 30 gauge
         a) pin 3 of 74LS157 to pin 1 of 74S86
         b) pin 9 of 74LS273 to pin 2 of 74S86
         c) pin 2 of 74LS157 to pin 3 of 74S86
     4. Use a 32K video buffer.  Specify either Pcjrmem /c or /e.
        If you use Jrconfig, use the v32 OR v64  switch and s1.
     5. Hint: When adding the wires, solder to the chip legs, not the board
        traces.  It is much easier to add/remove if this technique is used.
