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#positronJapes The morass grows as a 6th pod enters the fray so I can see what status the GPIB is returning to the CPU.

...and what it's showing is a constant /SRQ assertion, or Service Request. Unfortunately the OS9 code can't deal with this and just loops. Does anyone know anything about seemingly the only Positron floppy controller to exist in the world? 😆 /n

Here it is: binarydinosaurs.co.uk/Museum/Posit... Main ICs, top to bottom: TMS9914 GPIB controller HD68B44 DMA controller 6809 CPU 2K RAM EPROM TMS9909 floppy controller. The ROM is good and I can test the CPU and RAM in other machines. DMA stuff though, 🤷🏻‍♂️ Time to move some analyser clips 😁