Eprom Programmer 3.2 Extension

The following hardware extensions solve problems with weak parallelports and bad shielded cables as well as sporadically programming errors. You will need a ceramic 2.2 nF capacitor, a 100 nF capacitor and two 10 kΩ resistors for it.

Ceramic Capacitor, 2.2 nF

The ceramic capacitor C2 must be put into two via as shown on the picture below. The vias are right beside the 74HC157. One via is connected to pin 14 of the 74HC595 and the other pin is connected to ground (GND). Please don't forget to solder it from the bottom side.

Resistors, 10 kΩ

The both 10 kΩ resistors must be soldered on the bottom side of the etched print.
- Resistor R8 must be connected to pin 1 and pin 14 of the 74HC393 (IC1).
- Resistor R9 must be connected to pin 12 of the 74HC393 (IC2) and one Pin of the C6 (as shown below).

Overview for orientation. On the right side of the picture you will see the parallelport connector.

Resistor R8 must be connected to pin 1 and pin 14 of the 74HC393 (IC1):

Capacitor, 100 nF

The 100 nF capacitor must be connected to Pin 2 of the 74HC393 (IC2) and one pin of the C6 (as shown below). Please pay attention and don't make a short circuit on the board. Please note: the capacitor C9 is not soldered on the pictures above.