Oric Diag

Oric Diagnostics PCB

This is a reproduction of Mike Brown's Oric Diagnostic board and loopback harnesses, see Mike Brown's Diagnostic ROM and PCB

[!NOTE] Acknowledgements go to Mike Brown for posting the original design to his excellent website Oric And Atmos Support. Many Thanks.

[!CAUTION] USE AT YOUR OWN RISK. There is always the risk that the Oric Diagnostic board could cause harm to your Oric. Although I have tested the Oric Diagnostic board, there is no guarantee that it will work properly under all circumstances.

Repository Content

This repository contains the KiCad and gerber files associated with the Diagnostic board and loopback harnesses.

Changes from Mike Brown's Original Design

The following changes have been made from Mike Brown's Original Design:

• The clock circuit has been replaced by an ECS-100AX-010 oscillator.

• The LED resistors have been replaced with 220ohm values.

[!TIP] I still found the LEDs quite bright and you may consider increasing this value.

• LS components replaced with HCT.

• 3M holes have been added to allow for standoffs to be fitted.

For all other information about Mike Brown's original design please refer to Mike Brown's website

Ribbon Cable

The Oric Diagnostic board has been designed to be used with a 34-way ribbon cable and can be used partly when the Oric motherboard is still in the case, altough it is a bit difficult to use the NMI button underneath.

However for the most part it will probably be used when the Oric motherboard has been removed from the case, but remember the motherboard is normally upside down and hence the twist in the ribbon cable when used in this configuration.

[!TIP] Note the orientation of the ribbon connectors and red cable aligned to pin 1 and check connectivity back to the Oric motherboard before use.

Port A Loopback

The Port A loopback is designed to fit straight into the Oric printer port.

[!TIP] I found it difficult to remove the Port A Loopback when required. In the end I placed a pin header on the wrong side of the PCB and connected using a ribbon cable.

Keyboard Loopback

The Keyboard loopback is designed to fit over the end 10 pins.

[!NOTE] I struggled to find pin headers that fitted. In the end I used these pin headers but they are not a perfect fit.

Casette Loopback

The Casette loopback is not part of this repository please refer to Mike Brown's Diagnostic ROM and PCB page

1MHz Clock

[!NOTE] I have not had a need to use the clock source yet.

ROM

Please refer to Mike Brown's Diagnostic ROM and PCB page

[!NOTE] I used a 27C512 EPROM and copied the 16K ROM image four times to fill the 64K EPROM.

Jumpers

Please refer to Mike Brown's Diagnostic ROM and PCB page

[!CAUTION] I have not tested the jumpers A14=0, A15=0, INHIBIT VIA and VIA SEL

Testing

The Oric Diagnostic board has been tested on two Oric-1 computers. One Oric-1 passed all tests and the other failed on the Casette Input test (which was resolved by replacing the LM358 OpAmp). So unfortunately I have not yet had to use the Oric Diagnostic board extensively on a fully failed computer.