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The reset behaviour you describe is not normal, normally they reset cleanly every time but that is a minor niggle in the grand scheme of things.
SOC were either optimistic or knew full well that the user would have to fit a heatsink and omitted it to reduce their costs, either way you are correct, the regulator runs unacceptably hot without a heatsink. If you are running on a variable regulated supply you can help it out a bit by lowering the input voltage to the lowest at which the regulator continues to produce a reliable 5V output, which in practice will be between 7.5V - 8.0V.
If you are running on an unregulated supply marked '9V', try measuring the input voltage to the regulator, it might be a lot higher than 9V in reality.
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The power supply I'm using is a modern switching "wall wart" which is rated at 2A outputs 9.1v off load and a tiny bit less (~9.08v) when plugged into the MK14. Thats why I thought using a couple of diodes would drop the input to ~7.8v and dissipate some of the power before it gets to the regulator. The original manual suggested a resistor but I think diodes are a better option - in 1978 that would have been expensive but not so much today!
The regulator has a heatsink but its tiny, so I'll see if I can find one with longer fins. Unfortunately I made the regulator a bit snug against the socket for the INS8154 RAM/IO which I will address when I do rev 2 of the board!
Until then I'm celebrating with a can of
and a takeaway and spending a little time (re)learning how to program the SC/MP. I've learnt so much from making this despite the frustrations and once I've corrected the PCB I'll make the design files available for other people to play with .... and possibly have a go at the problem of programming Tesla 74S571 PROMs!