Technical Support Document 047 - 5/96
MODIFICATION FOR USING 2M EPROM ON STARLITE
55 MOTHERBOARD
This document outlines the modifications required to
run a 2 megabit EPROM on a Starlite 55 Motherboard.
This procedure requires intermediate to advanced soldering
skill and a familiarity with Printed Circuit Boards
and the nomenclature they use.
Instructions for Details A and C:
The chip on the motherboard labeled U5 is part number
74LS153. Another 74LS153 is "piggy-backed"
onto the chip that is on the board. The new chip is
soldered in place, with all pins connected to the old
chip, except pins 4, 7, 9, and 12.
Instructions for Detail B:
Remove the small blue capacitor next to the 28-pin
EPROM socket. Either de-solder it, or cut it's leads
with flush-cutting clippers. Make sure that no "stumps"
remain, as shorting with the new socket could result.
A new 32-pin EPROM socket will be installed on top
of the existing 28-pin socket. Before the new socket
is put into place, pin 28 on the old one must be cut
and removed from the socket body. This is most easily
done by using a pair of flush-cutting clippers to reach
under the corner of the plastic socket body and clipping
the pin, causing it to be pushed upward and out of the
body. Use a pair of needle-nose pliers or clippers to
lift the pin completely free from the socket. An empty
hole in the socket should be left in place of pin 28.
On the 32-pin socket, cut the thin lead part of the
four pins that will overhang the old socket. This will
reduce the chances of these pins shorting out with anything
on the circuit board. Do not cut pin 30.
Solder a short wire between pins 1 and 32 on the new
socket, leaving about 1 inch free off one end. Be careful
not to melt the pins out of position in the plastic
body.
Solder 6-inch wires onto pins 2 and 30 of the socket.
Make sure the soldered connections are as small as possible
to avoid shorting on the circuit board when the socket
is installed.
Install the socket into the old 28-pin EPROM socket.
Pins 1, 2, 31, and 32 should protrude past the pin 1
end of the old socket. In other words, pin 3 of the
new socket goes into pin 1 of the old one.
Solder the free end of the wire attached between pins
1 and 32 (from step #4) to the positive (+) end of the
nearby capacitor, as shown in the main drawing on the
previous page.
Solder the wire attached to pin 30 of the new socket
to pin 9 of the piggybacked chip U5.
Solder the end of the wire attached to pin 2 of the
new socket to pin 7 of the piggybacked U5.
Once all wires are soldered, the last
step is to cut a short trace on the back of the circuit
board. The diagram below shows which trace to cut. This
trace goes to pin 1 of U4, the system RAM chip. Use
a razor blade or X-Acto knife to cut the trace and remove
a section of it to assure that it does not re-connect
or short.
Solder a wire from pin 1 of U4 (at the end of the trace
just cut) to pin 36 of the microprocessor (U2). Be sure
not to let the solder short out adjacent solder pads.
Install the new EPROM into the 32-pin socket. Re-install
the motherboard into the Starlite enclosure and check
for proper operation.
If you have any problems or questions about this procedure,
please contact the offices of ZBE, Inc., at the address,
phone numbers or e-mail below.
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