wanderer wrote:
>
> Well,
>
> It finally is there, my own PDP 11/70, in working condition and with
> 1Mb in the memory box. The machine is placed in 1 H960 cabinet and
> has the original 11/70 top faceplate.
>
> I picked it up last Friday in the UK near London, and the whole
> trip did take 23 hours, including 2 two hour ferry trips.
> With it I got the documentation, engineering diagrams and a complete
> set of spare cpu boards.
>
> Although the machine is is working conditions, I will of course go
> through the (unpublished) list of steps before I apply the power
> to the backplane.
>
> Since the two bulk supplies are having 8 H744's (25A versions) I was
> just wondering about the feasebility of replacing them with standard
> PC XT power supplies (just for the 5V), as the usually deliver also
> between 25A and 30A, depending on the model. The large transformer in
> the bulk supply will then be replaced with a smaller transformer to
> deliver the LTC, DCLO, ACLO and +15V via the power monitor module
> which is still there.
Actually, I find the 5V regulators easier to work on than the typical PC
power supply, although not nearly as efficient. I am not sure that the
timing of the ACLO and DCLO lines could be retained if you use alternate
supplies. The current from the PC supplies may drop off much faster
than the H7420's when AC fails. In practice, I have never had much
trouble with the power supplies on my 11/70. Of course, I also have
spares just in case I ever do.
>
> Since I'm not going to use MASSBUS devices, two modules could be
> removed as they power a part of the MASSBUS backplane section.
Yes, H744 K & L can be removed if there are no RH70's.
>
> Of course, all the pins of the backplane will be checked and
> straightened if needed, and the card connectors will be vacumed before
> replacing the cards.
Good idea. Also check the output of the 5V regulators, they must be +/-
.1V of 5.00V. The output is very dependent on the stability of the AC
input voltage.
The biggest thing that is likely to need replacement are the fans.
Typically, the 4 in the bottom of the CPU burn up or seize up quicker
than the rest. Since there are a total of 17 fans between the CPU and
the power supplies, it is almost certain that you will be replacing
some. Mine was well cared for before I got it, and I still replaced 6
of the fans. If any look at all questionable, replace them with the
highest CFM fan that you can find. I use NMB 4715FS-12T-B50 110V fans
as replacements in mine.
>
> Any other tips I may need?
>
Make sure you install bus grant cards where needed and check the NPR
grant continuity on all the slots that may have had their NPG jumpers
cut. Since you said it was all in one rack, I assume the UNIBUS is
terminated in the CPU and does not extend to another shelf.
Sounds like you have MK11 memory? Be careful about the cabling to the
MK11 shelf. Several DEC documents have the connectors mis-labeled on
the drawings for the MK11. If you disconnect them, make your own notes
first about how they are connected. (I got burned once by following the
diagram that was wrong.) Disconnect the battery backup units from the
MK11 if the batteries are no longer any good.
Also, since you said it is all in one rack, if there is anything mounted
anywhere above the CPU in the H960 rack (MK11?), don't install the
covers on the front of the rack or the back door. You will not get
enough airflow to cool the CPU. DEC really didn't intend for anything
to be mounted above the CPU (except for a few shallow components that
don't restrict airflow). As far as I know, all later 11/70
configurations in H960 racks required a minimum of two racks, with the
MK11 in the second rack. Airflow will be even more important if you
don't have it in a controlled environment.
Good luck to you. I am glad to see another 11/70 in the hands of
someone who will care for it.
--
Doug Carman
pdp11_at_bellsouth.net
Received on Tue Jul 31 2001 - 14:54:23 BST