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From: kcwellsch@watmath.waterloo.edu (Ken Wellsch)
Newsgroups: comp.sys.dec
Subject: Re: PDP 11/24 VS 11/44
Message-ID: <1990Sep27.002342.27700@watmath.waterloo.edu>
Date: 27 Sep 90 00:23:42 GMT
References: <1990Sep25.201504.5605@uunet!konkord> <1990Sep26.135406.21647@ecn.purdue.edu>
Organization: University of Waterloo
Lines: 30

>> What does it mean when the DC ON light blinks and its NOT the
>> power suppy. Why does the DC ON light blink when grant cards
>> are not there/or not in the slot?
>
> I can give you some brief info here. The blinking DC ON light is indeed
> power supply problems, but not necessarily +5. Could be +/- 12, or +/- 15
> as well. The 11/24 and 11/44 do not share backplanes. They may look alike,
> but they are wired completely differently. DO NOT try to put an 11/24 CPU
> board into al 11/44 backplane, or vice versa. The 11/44 CPU is actually about
> six hex boards; the 11/24 CPU is one board. 

I had a flashing DC-ON light as well.  I tracked it down to a jumper (okay,
zero ohm resistor) that was enabling the monitoring of the 12 volt supply.
From what I could trace down, the 12 volts was there for the old 256K memory
boards while the newer 1Mb boards do not need 12 volts.  In fact my +12/-12V
lines are at +15/-15V.  So I disabled 12 volt monitoring (as this is a
jumper option) and my supply is otherwise within spec.  Someone may correct
my interpretation.  The jumper is on the M7090 card (I think there are about
20 or so "jumpers" and they are not obvious, at least not on my M7090).

I've got a glossy "relative performance" histogram that shows the 11/44
as about 1/2 that of a VAX 11/780 while the 11/24 appears to be about
1/4 a 780.  In fact they show the 11/23+ and 11/24 together on that chart. 
I believe the 11/24 is just a UNIBUS based Micro/F-11 chip as in the 23+.

Most of the PDP Unibus models have uniquely designed back-planes.  The
44 and 24 as said may look similar but are radically different.

-- Ken Wellsch
   kcwellsch@watmath.waterloo.edu