#Inktober 2019 Project – Post 2

Reverse Engineering the Atari 1020

The field service manual is quite helpful, but the pin numbers of the connectors are not labeled and there are no part number.

Between the manual and some measurements with my meter, I think I have it figured out.

Power Supply.

I do not have the original external (wall wart) power supply. You can tell it is AC from the schematic. I did some research and found out it is 9VAC. That goes through (2) 5V volt linear regulators (with a huge heatsink). One powers the stepper motors and all the logic. The other powers the pen up/down solenoid.

Basically, I should be able to power everything with a robust 5VDC power supply. I’ll probably use this style.

Switch Panel

This connects via a 6 pin molex SPOX 10013066 connector. The PCB side is Molex p/n 10321061. The power switch is a latching switch that connects the incoming 9VAC voltage.

The function switches are normally open, momentary switches that close to ground.

Here is the pinout of that cable.

Pen Solenoid

Then pen moves to and away from the paper using a solenoid. The schematic is amazingly complex here, but basically the voltage flows one way through it for pen up and the for pen down. It is a 5V coil with a resistance of 5.2 Ohm.

Stepper motors

There are (2) stepper motors. One is for the paper feed and the other moves the pen carriage. These motors are 5 wire unipolar motors. These are typically used by connecting the common to voltage+ and the other wires to transistors. If sequenced on one at a time, you get 4 independent coils.

The coil resistance of the paper feed stepper coils is 50 Ohm and the carriage is 60 Ohm.

Pen Change, Homing switch

There is a reed switch activated by a magnet in the pen carriage.

Printer Mechanism Cable

There is a 13 pin cable that connects everything in the plotter mechanism to the controller PCB. This uses a Molex connector p/n 511911300. The mate on the PCB is Molex p/n 22041131. The pinout is here.