LED driver modification for DSD Revision Beta-2
		     last revised 8/8/94 for v0.7

Keep a copy of the schematic diagram (ledmod.ps) handy for reference.

Parts required: 74HC04 (inverter chip), 2 green LEDs, 2 red LEDs, 1
yellow LED (or whatever mix is aesthetically pleasing), five 220 ohm
resistors (experiment with these values as desired), small
experimenters PCB (available at Radio Shack).

Find space for the board in the DSD chassis, drill any mounting holes
desired, solder 74HC04 on board.

Use hookup wire for all connections.

Integrated circuits tend to have some sort of a dimple, depression, or
semi-circle cut out of one end.  Hold the IC so that dimple is at the
top or upper left.  Pin 1 on the IC is at the upper left and numbers
proceed around in a U shaped pattern.

                 +---------\       /---------+
                 |          \     /          |
                 |           -----           |
              1A |  1                    14  | VCC
                 |                           |
              1Y |  2                    13  | 6A
                 |                           |
              2A |  3                    12  | 6Y
                 |                           |
              2Y |  4                    11  | 5A
                 |                           |
              3A |  5                    10  | 5Y
                 |                           |
              3Y |  6                     9  | 4A
                 |                           |
             GND |  7                     8  | 4Y
                 |                           |
                 `---------------------------'

The schematic uses the convention that inputs (xA) to the chip are
shown on the left, while outputs (xY) are on the right.  Note that pin
numbers are indicated next to each connection.  Make sure that each
connection is made to the correct pin --- the pin grouping on the
diagram is logical and NOT physical.  Use the pin numbers!




    LED driver modification for DSD Revision Beta-2 (page 2 of 2)


Inputs (indicated on the left side of the diagram) should be taken
from the following main DSD PCB locations:

ERF:  U1 pin 25
FC1:  U2 pin 24
FC0:  U2 pin 3
EMPH: U1 pin 3

These connections should be easy to make when the old LEDs are removed
from the main DSD PCB.

LEDs have one long lead and one short lead.  The long lead is the
anode.  The short lead is the cathode.  LEDs also often indicate the
cathode by a small notch at the base of the lens.  If you look at the
diagram, there is a little diode symbol drawn next to each LED
position.  The symbol is a triangle with a line across the apex.  The
anode is represented by the base of the triangle.  The cathode is
represented by the line across the apex of the triangle.

Make assemblies for the five new LEDs providing enough hookup wire to
reach the 74HC04.  Solder the wires connected to the cathodes of the
LEDs to make connection with the appropriate pins of the 74HC04.

Route power to the board.  The easiest place to get VCC (indicated by
a + with a circle around it on the diagram) is through the connection
previously used by the anode of D4.  Ground can be taken from a
variety of sources, notably the sides of R10/R11/R15 not connected to
the cathodes of D1/D2/D3.

Connect pin 7 to ground and pin 14 to VCC.

Install the 220 ohm pull-down resistors between the anodes of the LEDs
and VCC.

Make all "internal" chip connections.  Tie pin 2 to pin 3 and pin 11
to pin 12.

Examine your work.  All pins of the 74HC04 should be connected to
something.

Power up your DSD.  Verify that the power LED lights.  If not, check
power and ground connections to the board.

Experiment with a variety of digital input sources and verify that the
indicator lights behave as expected.