DEC8235 ICs

Vincent Slyngstad vrs at
Mon May 12 01:43:57 CDT 2008

>  Does anybody know of an equivalent or source for replacement DEC 8235 
> ICs?
> They're AND-OR-INVERT gates used as bus drivers on the TD8E (and probably
> other OMNIBUS boards).

Sourcing them is hard.  Maybe a pull from some other board that's been
designated "parts"?  I looked at some boards I have (where some idiot
shaved off all the metal from the edge connectors) but no 8235's there.

If you're driving a PDP-8 bus, maybe a pair of 74*756 for "A" and a pair
of 74*757 for "B" would allow a low parts count replacement?  (I think
one of the 757's enables is active high, though.)

Are you looking to repair a TD8E, specifically?  Those look like simple B/!A
switches, activated by SDRD and SDRC instructions.  If you are working with
an existing M868, that limits the desirable substitutions, because you 
want to rework every darned thing.  (OTOH, E01 has the spare inverter needed
by the 74*757.  You could socket E01, E05, E10, and E15, and make a little
daughter card to plug into the sockets.)


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