PDP-8/L: multiple failed 7440's date code 7005

From: Charles <charlesmorris_at_direcway.com>
Date: Sat Mar 1 20:50:53 2003

I have been busy debugging my PDP-8/L that last worked when stored
in the barn around 1995. It is slowly coming back to life - still
having problems with the core memory.

I have noted one strange and recurrent problem. So far I have
changed nine bad 7440's on a variety of modules, mostly core
drivers (G221, G228) which have had their outputs stuck, usually
high. All of them were labeled "DEC7440" with a date code of 7005!

Currently lower page locations won't write the lower bits 5-11 (or
at least return zeroes). The only common denominator for data bits
5-11 are at slot A09, where the MEM ENABLE 5-11 and MA ENABLE 5-11
lines are driven by, you guessed it, M617's featuring 7440's.
Haven't verified this yet but it's a safe bet where at least some
of the problem is!

Has anyone else experienced this problem? Seems like the chip
manufacturer must have had a few specks of dust in the fab room
that day in Apr. 1970...

-Charles
Received on Sat Mar 01 2003 - 20:50:53 GMT