11/34 irks

[Don North]

Tony Duell wrote:
>> Ya know... if you're going to design and manufacture a "modular" power 
>> supply like is in the 11/34A/BA11K, with those nice regulator modules... 
>> wouldn't you think it could be designed so you could pull them out to 
>> replace or add without having to remove the backend of the chassis? That's 
>> just silly.
>>
>> Perhaps I'm missing it. It appears that you take off the top cover, undo a 
>> holding screw in the back (one per regulator), and undo the connector for 
>> that regulator underneath. But the two screws underneath and inside? Those 
>> don't seem to be removable without taking off the back end of the chassis. 
>> Icky. GrumbleGrumble...
>
> It's not quite as bad... What you do is : 
>
> Remove top cover, loosen the top screw holding the PSU ('backend of the 
> chassis) on each side, and remove the bottmo 2 screws on each side. Then 
> swing the CPU to the vertical position (That's one reason why the rack 
> slides have a tilt mechanism) and the PSU will swing away from the 
> backplane are. Unplug the 8 pin mate-n-lock, remove the 3 screws and 
> slide the regulator out.
>
> The connecotrs are on the front of the regulators themselves, not the 
> connectors on the power distrbution PCB

Yup, for all their supposed 'engineering prowess' DEC did some mighty stupid
things sometimes, especially in the 1970s vintage systems.

Of course the above process only works well if you happen to have a 
BA11-K box
rack mounted with those cute DEC tilt slides. If not, then you are in for
a major overhaul. And by the way try and do all this without bending a
backplane pin...

Think the 11/34 in the BA11-K box is bad ... just try and get to the power
supply to replace the fan in a PDP-8m. You have to take the whole box apart.
To remove the P/S you need to move the backplane about an inch. To move the
backplane, well, that means pulling all the cards, ... what a pain! You'd
think by looking at the box the P/S would just slide right out, but no they
had to use pressfit bolts on the backpanel instead of regular screws. Jeesh.