Fitting battery backup to the KPC-2
            ===================================

You will need two IN4148 diodes, a 100K resistor and a 3V lithium battery.
Firstly, switch off the KPC-2 and take the unit out of the case.
Locate the 32K RAM chip, the '62256' 28 pin device, and isolate pin 28 from the socket. Connect a diode from +5V on the board (where pin 28 was located) to the RAM chip's pin 28. The cathode should be nearest the ram chip.

Secondly, connect the second diode from the lithium battery's +ve end to the RAM chip's pin 28, again cathode nearest the RAM chip. The -Ve end of the battery should then be connected to the 0V ground plane on the PCB. A 100K resistor may be required from pin 28 of the RAM chip to pin 20 (CS) on the RAM chip to ensure low power mode is attained when the unit is powered off. 

A « AA size 3V 750mAH lithium costs about two pounds at the most, making the battery backup very cheap and cost effective. It should also be possible to use two 1.5V primary batteries in series if space permits.

All the parameters, heard lists, node lists and PBBS messages are retained even when the power is completely removed. There is little use for the EEPROM "perm" command once the lithium is installed.

                  IN4148's
             I\ I         I /I
+5V o--------I >I----o----I< I---o +3V
KPC power    I/ I    I    I \I (battery)
         _______     I
    ----I_______I----o 
    I     100K       I
    o                I
Pin 20               I
of RAM chip          I
                     o Pin 28 of
                       RAM chip.

This has worked well on the KPC-2 and should be applicable for the KAM and KPC-4 units as well.

Neville G0JVU @ GB7MXM


PORTED AND REALIGNED FROM PC TO AMIGA FORMAT BY BOB G0LBQ - N6XDI.