11/34 irks

[Tony Duell]

> > 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.

I found they got a lot worse in the early 1980s.

> 
> 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

If your BA11-K is not in a rack, then loosen/take out the screws as 
above, then tip the CPU box onto one side. You can then ease the PSU away 
from the rest of the CPU and get the regulator out. 

> 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.

I am sure I've stated ARD's law of DECSA construction before -- 'The 
lower the importance of a part of a DECSA, the more screws hold it in 
place'. The PSUs are held in my 2 screws, the fan tray by 4 screws, but 
the grille over the fan tray is held on by an amazing 28 screws.

Removing the backplane from a DECSA is an entertainment. Everything else 
has to come out first...

-tony