SC518, v1.0, Assembly Guide

Click here for a list of the parts required to build an SC518, v1.0, Z80 CPU Card.

Important note: How to modify box headers

Experienced builders
There is only one suggested build option to watch out for. You can fit either a straight or a right angled header to P2. Other than that there shouldn’t be any surprises to catch you out, so experienced builders can just go ahead and populate the board.

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 circuit.

The picture below shows what a completed SC518, Z80 CPU Card should look like.


Fit and solder the 10k resistors R1 to R5 (shown below in red).

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

IC socket

Fit and solder IC socket for U1.

You may wish to fit a socket for oscillator X1. My preference is to solder this component, which you do later.

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


Fit and solder capacitors C1 to C5.

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

Jumper Header Pins

Fit and solder jumper header pins JP1.

This header may need to be cut down from a longer strip.

Clock Source Header

Fit and solder connector P2.

You can either fit straight pins or angled pins.

Angled pins give better access when mounted on a backplane, but straight pins are less obtrusive.

This header may need to be cut down from a longer strip.

Take care to ensure the pins are perpendicular (straight pin) or parallel (angled pins) to the circuit board.

Bus connector

Fit and solder the bus connector, P1. This can either be a right-angled box header or right-angled header pins. The box header is recommended.

Take care to ensure the connector is fitted such that the card will stand vertically when fitted to a backplane. A good method is to just solder two pins, one at each end, and then check it looks correct. Then solder two more, one at each end but in the other row, and check again. At each stage, if necessary, adjust the position by heating the required solder joint and moving the connector slightly. Solder two pins in the middle of the connector and check again. Then solder all the others.


Fit and solder the 7.3727 MHz oscillator, be sure to fit it the correct way around.

Pin 1 of the oscillator is normally indicated by a ‘sharp’ corner, while the other three corners are rounded.

Pin 1 on the circuit board is also indicated by a ‘sharp’ corner, while the other three corners are rounded.

I prefer not to fit a socket for these oscillators as they stick up quite high and have exposed metal on top, increasing the risk of accidental short circuits. Also, they are quite heavy and are only held in the socket by four pins, so additional securing is often needed.


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.


Fit a jumper shunt to JP1, as shown below. This selects X1 as the clock source for the system.

Integrated Circuits

Insert the IC U1 into its socket, taking care to insert it the right way around, as illustrated below. Be careful not to bend any legs over. ICs are usually supplied with the legs slightly spread out making them difficult to insert. It is best to bend the two rows of legs so they are parallel before inserting them. Remember, these components can be damaged by static electricity so if possible earth yourself and the components while handling them.

Getting Started

The SC518 User Guide includes a brief guide to getting started.

Homebrew 8-bit retro computing