PDP 11/40 AC LO and M7235 (Status K5 Module)

tony duell ard at p850ug1.demon.co.uk
Sun Mar 8 11:15:45 CDT 2015

>  With the cable removed from the h742a connector, P9 says DC LO and AC LO
> are 3.53v, which is lower than the expected +4.8v.  This tells me there is

Have you confirmed these are steady DC voltages Or could the signals be oscillating
with that as the average value?

There is a capacitor in the H742 that if it fails (and it does...) the ACLO and DCLO will
oscillate at mains frequncy (or probably twice it). Certainly on the 11/45, this really
confuses the CPU microcode. It's the obvious smoothing capacitor for the supply to
the ACLO and DCLO circuit.


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