RE: Schematic for DEC H7441 (not the H744!)

[Robert Armstrong via cctalk]

>Eric Smith  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.

Bob

Re: Schematic for DEC H7441 (not the H744!)

[Eric Smith via cctalk]

DEC MK11-B Field Maintenance Print Set, October 1977

http://bitsavers.trailing-edge.com/pdf/dec/pdp11/1170/MK11-B_Field_Maintenance_Print_Set_Oct77_part2.pdf

pages 27 to 36 of the PDF file

Schematic for DEC H7441 (not the H744!)

[Robert Armstrong via cctalk]

  Is there a schematic for the H7441 regulator anywhere?  There are several
out there for the H744 but, although they are plug compatible, the H7441 is
totally different.   The H744 uses an LM723, but in the 7441 DEC appears to
have rolled their own regulator using a bunch discrete parts and opamps.

 

Bob