pdp11/45

From: Jacob Ritorto <jritorto_at_nut.net>
Date: Sat Jun 19 09:38:52 1999

Hey All, sorry I took so long to get back to this topic, but things have
been hectic and there's been no time for Geek Stuff. :( :( :(

I removed the extraneous things from the bus (namely the external box of
memory and the three core SUs), so now I have only the 11/45 backplane
with an M930 in the last slot. Still the same symptoms on the front
panel.


        The probe of J14 revealed the following:

        on 2&3: exactly 15VDC (this is the 15v source you ask about being
present and correct, isn't it?)
        on 8 : about 4VDC
        on 10 : Zero.
        on 12 : about 4VDC

To answer a few of your other questions:
        I don't have a KM11 maintenance board.
        I have the 8-pin, flat power connectors on my CPU.
        
Which schematics are you using?
What should I do next?


thank you.

jake


 On Thu, 27 May 1999, Tony Duell wrote:

> >
> > Hello Classiccmp.
> > I recently acquired a nice, rust-free, mostly-original 11/45 from
>
> You're in luck. The 11/45 was the first '11 that I obtained, and I have
> the manuals for it (printset, maintenace manual, etc).
>
> > an old lisp hacker in Los Altos Hills, CA. He told me that it had been
> > running the last time he'd powered it up, which was in 1984 IIRC, but
> > sadly, something has gone awry and it won't run now, though it seems to be
>
> It can be got to run again. I am certain of that.
>
> I am going to assume that you don't have the KM11 maintenance board,
> useful though it would be.
>
> > has 12 KW of core as well, so I guess I could cut the bus down a bit more
> > for the purpose of debugging.
>
> You don't need _any_ memory to start with. As this is an 11/45, the core
> can't be on the processor backplane (which has special slots for
> MOS/bipolar boards only). So stick the M930 in the top of the rearmost
> slot (slot 28 IIRC) of the CPU backplane for the moment. You'll not be
> able to do a lot, but the CPU will at least talk to the frontpanel in
> that mode if everything is working right.
>
> >
> > Mode of failure is such:
> > I powered up the shortened system and the front panel lights lit
> > [excitement]. Then I tried to examine some memory locations via the
> > panel, but when I hit HALT, the RUN light stayed lit. I tried every
>
> That is a classic indication on the 11/45. If one of ACLO or DCLO (I
> forget which) is asserted, the CPU microcode goes into a tight loop and
> won't listen to the panel.
>
> This is either something on the bus pulling one of those lines, or a
> fault in the PSU/wiring.
>
> > combination of switches I thought was appropriate, but the RUN light
> > wouldn't go off. (Sounds like a simple bus error, really.) Upon
> > realizing that something was amiss, I decabled all the power connectors
> > from the logic and tested the voltages, which, surprisingly, were all
> > about 6%-9% above spec (and I'm not too sure that my VOM is accurate even
>
> Yes, the old power modules will rise a bit off-load. That is nothing to
> worry about.
>
> Which version power cableform do you have? Old machines have a
> distribution PCB inside the CPU box with 8 pin mate-n-lock (flat)
> connectors on it. Later machines have a distribution panel on the frame
> at the top right of the CPU with 6 and 15 pin connectors on it.
>
> I have manuals for both types, BTW.
>
> > though it's analog). I didn't readjust the voltages, but reconnected the
> > power cables to the logic boards and retested the voltage levels. All
> > stayed about the same except for the -15VDC. It dropped to about 2V. Same
> > reading on both -15V regulators, by the way, and they seem to be connected
>
> This you aare going to _love_...
>
> There are 3 -15V sources in an 11/45 PSU. There's an H745 regulator in
> both power supplies (and they do, indeed feed different parts of the
> machine). There's also a -15V feed from the power control board in the
> lower PSU (this board generates what is normally considered to be a +15V
> rail. On the lower PSU, the +ve side goes to ground, and the -ve side to
> the rest of the machine).
>
> There is also a +15V supply from the top PSU power control board. This is
> needed by the H745 regulators. Is this pressent and correct?
>
> Looking at the schematic, it appears that if DCLO is asserted (low), then
> Q3 on this board will turn on. This will turn on Q2 and shut down the
> +15V regulator. Aha.... But only if DCLO is asserted by the PSU, not by
> anything else in the machine.
>
>
> Start on J4/P14 (12 pin mate-n-lock) on the top PSU. On the transformer
> housing at the front of the PSU, not on the regualtor blocks.
>
> Pins 2 and 3 are the +15V output (They're linked together inside the
> PSU). Pin 12 is DCLO (this is pulled up by resistors on the bus
> terminator, so you must have the rest of the machine connected). Pin 8
> and 10 (NOT commoned inside the PSU) are the ACLO pins.
>
> Let me know how you get on. As I said, I have all the schematics of this
> machine (including the PSU), and I've repaired mine on the odd occasion...
>
> -tony
>
>
>
Received on Sat Jun 19 1999 - 09:38:52 BST