Iomec disc drive?

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sun Jan 4 22:45:27 2004

> The DTL already tripped me up once. I had a J/K flip flop with both Q and
> -Q low. Turns out -Q was wired with the output of another gate as an
> apparent ECO (wasn't on the schematic). Sigh. At least with TTL you have
> the clue of the part being open-collector to help you realize someone did
> that. 8^)

Years ago I was working on a thing called a 'Solatron DTU', which was
basically a data logger add-on for a DVM (it had a 20 channel input
multiplexer, a real time clock, and output boards for a Facit 4070 punch
and an ASR33 IIRC). Anyway, it wa all DTL inside.

I found a (genuinely) dead JK flip-flop. Found the pinouts from the
schematics (which fortunately I have), and thought I'd found a
pin-compatible TTL replacement. Popped it in, and the darn thing still
didn't work. No, it wasn't a wire-AND connection... It turns out that the
DTL and TTL chips have the same pinout _except_ that Q and Q/ are swapped
round, and that was easy to miss when looking at the databooks.....

-tony
Received on Sun Jan 04 2004 - 22:45:27 GMT