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I got them pre-programmed. With the latter version with the tape routines and the "0000 00" startup display.
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In that case I think yours will be MH74S571 PROMs rather than original DM74S571s?
Let us know how you get on. I should think it will go OK because you have already proved the system using substitute RAM.
Until TonyDuell mentioned it, I didn't know the 74LS157s could be so troublesome. I should look into sourcing some good working spares for my MK14 while the originals are still working.