Schematic for DEC H7441 (not the H744!)

Robert Armstrong bob at
Wed Jun 17 18:49:51 CDT 2020

>Eric Smith <spacewar at> wrote:
>DEC MK11-B Field Maintenance Print Set, October 1977

  Thanks, Eric!  I was just about to post that I discovered it's also in the PDP-11/04 maintenance print on Bitsavers, although it's not in the 11/34 print - go figure...

  I didn't actually need the schematic, although I certainly used it this time.  The H7441 has a giant inductor (L1 in the schematic) that's physically bolted to the PCB.  It a U-channel thing that looks like a transformer but is actually just a big 30+ amp choke.  Some PCB layout guy decided it was a good idea to run the +5V output and ground traces directly under this choke so, unless it's elevated above the PCB, it will short the output!  I think it must have originally had some kind of rubber or fiber washers underneath it, but in mine the washers had disintegrated and were nowhere to be found.  I could tell that it was shorted somewhere, but I kept thinking that it must be a bad capacitor or a shorted crowbar, and I'm embarrassed to say that it took me more than an hour to figure out that it was the frame on the choke.  I carved up a rubber grommet with an X-acto to make some spacers and now it's as good as new.


More information about the cctalk mailing list