PDP-11/45 RSTS/E boot problem

Warner Losh imp at bsdimp.com
Mon Feb 4 13:06:17 CST 2019

On Mon, Feb 4, 2019 at 11:35 AM Paul Koning via cctalk <
cctalk at classiccmp.org> wrote:

>  The spec says allowed tolerances are +/- 5%.  He knew the reality for
> correct operation was -0%, +5%, so he tweaked all the supplies to read a
> hair above nominal.

Ah, the good old days...  I recall our PDP-11 tech tweaking +5V from 5.05V
to 4.95V and back again to demonstrate that tiny differences matter a lot
on one of the cranky 11/23+''s we had after I made a particularly unhelpful
teenage smart ass remark... The 11/23+ wouldn't boot at the slightly lower
than full voltage. It as cranky for a couple of years. Before that unit was
retired, the 5V and 12V rails had been tweek up to 5.2V and 12.5V in an
effort to keep the system alive long enough to transition customers from it
to a new Vax installed to deal with the growth in demand...  In the end, we
put that 11/23+ back in service for developers with a different disk
controller and it was happy back at +5.05V / +12.1V...


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