PDP-11/45-55 CPU fan assemblies

tony duell ard at p850ug1.demon.co.uk
Sat Nov 7 07:57:14 CST 2015

> Hi, all: I recently bought a PDP-11/45 [well, a /55, to be technical; the /45,
> /50 and /55 are completely identical except for i) the memory options
> installed at purchase, and ii) the printing on the front console :-], but
> alas, when I looked closely, it is missing both upper and lower CPU fan
> assemblies. (No doubt, removed to allow cannabilization of the fans, to keep
> another machine running.)

IIRC that 21" mounting box (and I assume therefore the fan assemblies) was used
on other machines like the 11/40 (some versions), the 11/70, etc. I am not suggesting
you raid one of those for parts, but it might be something else to look at.

>  iii) failing
> all of the above, be willing to take lots of pictures, and some measurements,
> of a set, to aid in making reproductions.

I do have an 11/45 here with the original fan trays. The top one is easy to get at
and measure, but IIRC the bottom one is a right pain, involving removing all the
boards and dismantling the very fragile card guides. I can take pictures of the
outside (I think, although that will be hard due to the limited distance in which 
to work) but I really would rather not take it apart unless there is no alternative.

By Murphy's law, the top one is the simpler one. It is a flat bit of metal with
grilles punched in it over 5 (IIRC) fans. What we call a 'piano hinge' down
the RHS, 2 Dzus fasteners (same type as for the CPU side paneL) near the
left corners. Fans mount on the underside, there is another punched grille
panel over the bottom of all the fans secured by 4 screws to each fan. It
is one panel, not one per fan.

The bottom tray is more complicated, it is a bent metal trough-like thing. It
fixes to the bottom of the CPU box, the fans are inside it.


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