Click here for a list of the parts required to build an SC516, v1.0, Z80 Processor 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 (serial port). 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 SC516, Z80 Processor Card should look like.
Resistors
Fit and solder the 10k resistor R1 (shown below in red).
Fit and solder the 1k resistor R2 (shown below in green).
These can be fitted either way around, as they are not polarity dependent.
IC sockets
Fit and solder IC sockets for U1 to U5 (shown below in red).
You may wish to fit a socket for oscillator X1 (shown below in green). My preference is to solder this component, which you do later.
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 around too.
Capacitors
Fit and solder capacitors C1 to C7.
These can be fitted either way around, as they are not polarity dependent.
Resistor network
Fit and solder the 8x10k resistor network, RN1.
The 10k network will be marked 102.
Take care to fit the resistor network the correct way around. Pin 1 is usually marked with a dot. This end is indicated on the PCB and on the illustration below.
Light Emitting Diode (LED)
Fit and solder green LED, LED1.
If using an angled LED the polarity is predefined and matches the PCB.
If using standard LEDs care must be taken to ensure they are fitted the correct way around.
It is important to fit the LED the correct way around. LEDs usually have a small flat side to indicate the cathode (the negative end). This should be positioned to match the flat side shown on the circuit board (illustrated to the right). Also, the cathode pin on the LED is usually shorter than the other pin (the Anode).
Power Header
Fit and solder header pins JP1.
This header may need to be cut down from a longer strip.
Serial Header
Fit and solder connector P2.
You can either fit straight pins or angled pins.
Angled pins generally give better access when mounted on a backplane, but fit straight pins if the card is to be used with card guides as suggested in the Z50Bus specification.
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.
Inspection
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, shown below in blue. This allows the circuit board to be powered from the serial port.
With a suitable FTDI style TTL level serial to USB adapter connected from P2 to a powered USB socket.
Check the supply voltage on this circuit board between U5 pin 7 and U5 pin 14. This should be 4.5 to 5.5 volts, preferably 4.75 to 5.25 volts. Unplug the serial adapter.
Oscillator
If you decided to 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.
Integrated Circuits
Insert the ICs into their sockets, taking care to insert them 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 SC516 User Guide includes a brief guide to getting started.
Fault Finding
Check there are no chips with bent legs and thus not making contact with their socket, carefully inspect all soldering, check all the chips are inserted the right way around, check all the components are in the right place.
With a suitable FTDI style TTL level serial to USB adapter connected from P2 to a powered USB socket, check the supply voltage on this circuit board between, say, U5 pin 7 and U5 pin 14. This should be 4.5 to 5.5 volts, preferably 4.75 to 5.25 volts.
Check the LED is on. If it is not, then check the LED is the correct way around. Also check the RESET signal is high but goes low when the reset button is pressed. The LED should light when U4 is powered and working, and the RESET signal on U4 pin 15 is low.
If the LED is working, check it flashes off then on again, either once or twice after a reset. If it flashes then the board is running code successfully. This would indicate that all the main components are generally working. If the LED flashes off once after reset the system has detected a serial card plugged into one of the Z50Bus. If it flashes off twice it has not detected a serial card and is using the onboard serial port (P2). If it keeps flashing the self-test has failed, most likely indicating the RAM is not working.
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