Replacing failed powersupplies on qbus PDP-11s

[Pete Turnbull]

On 29/01/2009 16:59, Tobias Russell wrote:

> I have a couple of uPDP-11 boxes (BA23) with failed power supplies.
> Being no expert on repairing switch mode power supplies (and to be frank
> slighly scared of trying), is there any reason why I shouldn't adapt a
> ATX power supply from a PC to provide the required voltages?
> 
> Most ATX power supplies offer pretty meaty 5V and 12V feeds plus a
> fairly small -12V (~0.3A) feed.
> 
> Will I need to generate a LTC/BEVENT L signal if I go down this route?

Yes, you will, although (a) it's not hard, and (b) you could simply add 
a timer card that does it, like a KWV11.  We had this discussion very 
recently, over a BA11-V box.

However, that's not all you need.  There are two distinct bus signals 
that tell the CPU (and potentially other devices) that the power is 
good.  There's one to say the AC supply to the PSU is good (BPOK) and 
another to say the DC is good (BDCOK); these are essential to some 
processors for a clean startup and are used to control the CPU shutdown 
and power-fail/restart.

> Finally, does anyone know of any good guides on repairing switch modes?
> Whilst not keen, I guess I should bite the bullet (hopefully not
> literally) and learn how to repair them.

Tony :-)

-- 
Pete						Peter Turnbull
						Network Manager
						University of York