TECHNICAL BULLETIN                                     COPYRIGHT   1986



DATE:                   August 5, 1986

REVISION DATE:          August 5, 1986

BULLETIN NO:            200:3

PRODUCT:                26-3860  Tandy 200

SUBASSEMBLY:            AX-9505  Memory board

SUBASSEMBLY REVISION:   All
______________________________________________________________________________

PURPOSE:  To keep the computer from locking up after AC power is lost with
          the Ni-Cad upgrade installed.
______________________________________________________________________________


DISCUSSION:

A problem has shown up while using the Tandy 200 with the Ni-Cad upgrade and
an AC adapter.  If AC power is lost and the customer pushes the ON/OFF button
before removing the adapter plug from the computer, the unit will lock up
tight even if he later removes the adapter plug.  This problem can be
corrected by installing a 1N914 diode between the Ni-Cad batteries and the AC
source.


PROCEDURE:

On the memory board of the computer, two jumpers were installed during the
Ni-Cad upgrade (J301 and J302).  Refering to figure 1 of the Memory PCB,
remove the jumper wire J302 and in its place install a 1N914 diode.  Note the
proper orientation of the diode, the cathode (banded) end should be near the
silkscreen J302 label.  Because of the space restrictions, trim the diode
leads short and check for any solder or wire shorts.

Figure 2 is the power supply section of the main pcb.  It shows the schematic
change involved with this procedure.

Check for proper operation using the AC adapter and then the Ni-Cad batteries
alone.


      1N914 diode     National Parts # DX-0010        Catalog # 26-6052








                                  TB 200:3
                                 PAGE 1 OF 2

   TECHNICAL BULLETIN                                     COPYRIGHT   1986




















                           Figure 1.  Memory PCB.




























                Figure 2.  Power Supply Section of Main PCB.






                                  TB 200:3
                                 PAGE 2 OF 2