SC103, v1.0, Assembly Guide

Click here for a list of the parts required to build an SC103, v1.0, Z80 PIO Module.

Experienced builders can just go ahead and populate the board. There shouldn’t be any surprises to catch you out.

This guide assumes you are familiar with assembling circuit boards, soldering, and cleaning. If not, it is recommended you read some of the guides on the internet before continuing.

First check you have all the required components, as listed in the parts list.

Before assembling it is worth visually inspecting the circuit board for anything that looks out of place, such as mechanical damage or apparent manufacturing defects.

If you have a multimeter that measures resistance or has a continuity test function, check there is not a short on the power supply tracks. Connect the probes to each terminal of one of the capacitors, such as C1. This should be an open circuit, not a short.

The picture below shows what a completed SC103 Z80 PIO Module should look like.

IC sockets

Fit and solder IC sockets for U1, U2, and U3.

Be sure to fit them with the notch matching the legend on the circuit board, so you do not end up fitting the IC the wrong way round too.

The sockets should be fitted in the positions shown below.


Fit and solder capacitors C1 to C4.

These can be fitted either way round, as they are not polarity dependent.

Resistor Network

Fit and solder the 8x10k resistor network.

This must be fitted the correct way round. The component should have pin 1 marked with a dot, as illustrated right.

Bus Connector

Fit and solder bus connector P1.

You can fit just a single row header, as used by the RC2014 Standard bus, if you wish.

To prepare the header, it should first be cut to length (if starting with a strip more than 39 pins long) and then unwanted pins must be removed. If you want to make the board as easy to insert and remove as possible, you can remove all the pins in the second row except those shown on the schematic as used and indicated below in green.

Take care to ensure the pins are parallel to the circuit board so that the board will be vertical when plugged into a backplane.

Header Pins P2

Fit and solder the
double row right-angled male header pins P2.

Take care to ensure the header pins are parallel to the circuit board.

Header Pins P3

Fit and solder the right-angled male header pins, P3.

Take care to ensure the pins are parallel to the circuit board.

Header Pins P4

Fit and solder the right-angled male header pins, P4.

Take care to ensure the pins are parallel to the circuit board.

Jumper Pins

Fit and solder the jumper pins for JP1 and JP2.

JP1 and JP2 are combined as a single, 2 row by 2 pin header.

Address Select Switch

Fit and solder the 6-way DIP switch SW1.

Take care not to overheat this component when soldering.

Address Select Switch

Fit and solder capacitor C5 .

The PCB allows for a radial or axial capacitor. In order to build a low profile board, the capacitor should lay on its side. An axial capacitor would be most secure in this configuration, but there is limited length allocated and you probably don’t have one!

You can fit a radial capacitor on its side, but it is not as secure as an axial package as both leads come out of the same end.

It is important to fit this capacitor the right way round.

The PCB’s legend shows a plus and minus signs next to the round outline of a radial packaged capacitor, as illustrated to the right. It also shows the alternative plus position for an axial capacitor (at the top of the rectangular area). In both cases the negative terminal is at the bottom.

The images to the right show the typical markings of the negative terminal of the capacitor.

PCB Legend
Radial Capacitor
Axial Capacitor


Remove any solder ‘splats’ with a brush, such as an old toothbrush.

Visually inspect the soldering for dry joints and shorts.

Clean the flux off with suitable cleaning materials.

Visually inspect again.

Before fitting the ICs, plug the board into an RC2014 backplane with no other boards fitted. Power the backplane and perform the following checks with a voltmeter:

  • Check the supply voltage on the PIO module, between, say, U1 pin 10 and U1 pin 20. This should be 4.5 to 5.5 volts, preferably 4.75 to 5.25 volts.
  • Check the interrupt enable input (IEI) on connector P4 is being pulled up to at least 4.5 volts.
  • Check each address switch input (Q2 to Q7) on U1 is being pulled up to at least 4.5 volts when the appropriate switch (SW1) is Off (open) and drops to less than 0.4 volts when the appropriate switch (SW1) is On (closed).

If all is well, power down and remove the PIO module.

Integrated Circuits

Insert the ICs into their sockets, taking care to insert them the correct way round, as illustrated below. Be careful not to bend any legs over.


There is no need to fit any of the jumper shunts yet.

Set the DIP switches as shown below. This sets the address to the range 0x68 to 0x6B.

Now plug the PIO module into the RC2014 backplane together with your normal working set of modules. Power up and check the system is working as usual.

Details of how to use this module can be found in the SC103 Z80 PIO User Guide.

Homebrew 8-bit retro computing