D'oh - Re: PDP-11/23 H786 PSU Fault Finding - test-drb@ccmp.vtda.org

29 Jun 2009

...
  On 6/29/09, Tony Duell <ard at
p850ug1.demon.co.uk> 
...
   My first
question is 'do you have enough load on the  5V line?'. If you
  don't, the chopper circuit is running very
'lightky',  and probably the
  12V side isn't getting enough power to work
properly.  I've certainly had
  DEC supplies where the 12V output is low untill I
 loaded the 5V output. 
--- On Mon, 6/29/09, Ethan Dicks <ethan.dicks at gmail.com> wrote:> 
...
  There's a load-board for the uVAX2000/VS2000 box
for use if
 you don't
 have an internal hard drive.? AFAIK, that's why it's
 needed - to
 ensure enough load on the +5V line for the +12V regulator
 to work. 
Well, as both Tony and Ethan noted, you do indeed have to load the +5V line up before the
+12V line will regulate properly.

I put a low wattage automotive turn signal bulb across the +5V line and the +12V line
jumped right back to where it should be.

Many thanks. I can now reassemble the 11/23 and get it back in the rack.

Don't you love it when stuff works ! Now I just have to fix that RLV12...

-Dave